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Although oncogenic fusions involving the neurotrophic tropomyosin receptor kinase (

) genes were first noted more than 30 years ago, the growing use of next-generation sequencing has only recently revealed their presence across a wide range of tumor types and piqued interest in their potential as anticancer targets.

Just as ALK inhibitors developed quickly as a lung cancer treatment, drugs targeted at the tropomyosin receptor kinase (TRK) protein family, encoded by the 

 genes, are following a rapid bench-to-bedside trajectory. The FDA has granted breakthrough therapy designations to entrectinib and larotrectinib (LOXO-101) for patients with metastatic 

 fusion—positive solid tumor types, and several other agents are being tested in clinical trials (Table).

Meanwhile, the development of acquired resistance is already being addressed by the advancement into clinical testing of secondgeneration agents with efficacy in resistant tumors, even before the first generation has received FDA approval.

Most intriguingly, the low prevalence of 

 fusions in individual tumor types has necessitated the use of novel clinical trial designs, such as basket trials. The astonishing efficacy of TRK inhibitors in 

 fusion—positive patients, regardless of histology, exemplifies the potential of the “tumor-agnostic” treatment paradigm.

In the mid-1980s, an oncogenic fusion of the 

genes, observed in a colon tumor sample, was among the first chromosomal rearrangements identified in cancer.

 Since then, this type of molecular abnormality has been widely recognized as a driving event in a broad array of tumor types

, and the development of drugs designed to target such aberrations has greatly improved outcomes in some forms of cancer.

encodes the TRK A protein that, together with TRK B and C (encoded by the 

 genes, respectively), form the TRK family of proteins. These receptors conduct signaling pathways that play a key role in the development of the central and peripheral nervous systems.

TRK signaling is activated by the binding of neurotrophin ligands, predominantly nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3); they bind, respectively, to TRK A, B, and C (Figure).

As with other tyrosine kinase receptor—driven pathways, ligands bind to the part of the receptor that extends out of the cell. This causes 2 receptor molecules to pair up, driving phosphorylation of critical tyrosine residues on the portion of the receptor that protrudes into the cell and creating docking sites for intracellular proteins that contain specific domains.

In this manner, the signal is transduced inside the cell and subsequently propagated further downstream as the recruited adaptor proteins turn on other pathways, including PI3K, MAPK, and PLCγ. Ultimately, the signal reaches the nucleus, initiating a variety of transcriptional programs that mediate cellular outcomes, in this case regulating the proliferation, growth, and survival of neurons.

 gene abnormalities have been described in different tumor types, including amplifications, deletions, mutations, and altered splicing of TRK messenger RNA (mRNA) transcripts. Few of these abnormalities have been functionally characterized, and even fewer have been proven to be oncogenic, with the exception of an in-frame deletion and mRNA splice variant in acute myeloid leukemia and neuroblastoma, respectively.

The best-characterized oncogenic role is for chromosomal rearrangements involving the 

 genes. Most commonly, these rearrangements result in gene fusions in which the 

gene is broken apart, and the portion containing the kinase domain is fused back together next to a different gene, causing the TRK protein to become activated even in the absence of its ligand. This promotes cancer formation by driving several of the cancer hallmarks, including unchecked cell proliferation and growth, through the TRK pathway.

The development of next-generation sequencing technologies has greatly expanded appreciation of the role of NTRK fusions in the development of cancer. To date, multiple fusion partners that play oncogenic roles across 19 tumor types have been identified for all 3 NTRK genes.

In the more common types of cancer, such as lung, colorectal, and head and neck cancers, 

 fusions occur at a low frequency, but they represent the dominant driver in certain rarer types. For example, the 

 gene fusion is found in all cases of mammary analog secretory carcinoma (MASC) and in 93% of secretory breast cancers

gene fusions are found in up to half of all pediatric patients with diffuse intrinsic pontine glioma and non-brainstem glioblastoma.

Numerous multikinase inhibitors already on the market or in clinical development have been shown to inhibit the TRK kinases to some extent, but they have not yet been tested specifically in patients with 

Entrectinib and larotrectinib represent the first of a growing number of oral small-molecule inhibitors with potent activity against all 3 TRK proteins. Entrectinib also targets the ALK and ROS1 kinases, while larotrectinib is the first drug in clinical development that selectively inhibits the TRK proteins alone.

Both front-runner drugs have shown potent clinical activity in patients with metastatic or unresectable solid tumors, most promisingly in patients harboring

 fusions. As a result, researchers have begun to limit clinical trial enrollment to patients whose tumors harbor these alterations, revealed through biomarker analysis.

Another notable feature of entrectinib is its ability to cross the blood-brain barrier, which could make it more effective in patients with primary brain tumors or brain metastases. Larotrectinib may also be able to penetrate the blood-brain barrier, though to a much lesser extent.

Entrectinib has been evaluated in 2 phase I studies: ALKA-372-001, with 54 patients, and STARTRK-1, with 65 patients. Both studies enrolled participants with a range of solid tumor types, including primary brain, head and neck, breast, renal cell, ovarian, sarcoma, and melanoma; however, 60% of the participants had non—small cell lung cancer (NSCLC).

Approximately half of the patients enrolled had an 

gene fusion; responses across both studies were limited to 25 patients with mutations who had not previously been treated with a tyrosine kinase inhibitor. Among 3 participants with 

 fusions, the response rate was 100%, with the most durable response of over 15 months observed in a patient with colorectal cancer with an 

 fusion. Another patient with a glioneuronal tumor with a BCANNTRK1 fusion experienced stable disease and, according to 3-dimensional volumetric assessment, the tumor burden was reduced by 60%.

Entrectinib was well tolerated in phase I trials, with fatigue, dysgeusia, paresthesia, nausea, and myalgia the most commonly observed adverse events (AEs). Based on the positive data from these trials, the FDA awarded entrectinib a breakthrough therapy designation in May and it is being evaluated in the phase II STARTRK-2 study at a dose of 600 mg daily.

Findings regarding larotrectinib created a significant buzz at the American Society of Clinical Oncology (ASCO) Annual Meeting in June. The data came from an integrated analysis of ongoing phase I/II studies involving 55 participants, including 12 pediatric and 43 adult patients, with 17 unique cancer types. They received larotrectinib primarily at a dose of 100 mg twice daily on a continuous 8-day schedule.

The overall response rate, based on investigator assessment for 50 patients for whom confirmatory data were available, was 76% (95% CI, 0.62-0.87), including a partial response in 64% of patients and a complete response in 12%. The 5 patients who joined the study too early for confirmatory scans had at least a partial response to larotrectinib.

In a separate analysis of 17 pediatric patients with heterogenous tumor types, also presented at ASCO, responses were seen exclusively in those with 

positive patients experienced confirmed responses regardless of tumor type, and the drug was well tolerated, with an AE profile that included vomiting, nausea, and fatigue.

At least 6 additional drugs that target the TRK pathway are in clinical development (Table). Early results from an ongoing first-in-human trial have been reported for DS-6051b, which inhibits TRK A, B, and C, in addition to ROS1. At the time of analysis, 22 patients with tumor types including neuroendocrine carcinoma and NSCLC had been enrolled and were being treated with once-daily doses of 50, 100, 200, 400, 800, or 1200 mg.

Table. TRK inhibitors in Clinical Development

Two dose-limiting toxicities occurred at the highest dose, both involving grade 3 transaminase elevations. The maximum tolerated dose was 800 mg once daily. Two patients showed partial responses; notably, 1 of these patients had progressed on both crizotinib and ceritinib. The most frequent treatment-related AEs were diarrhea, nausea, vomiting, dehydration, dizziness, dysgeusia, and fatigue.

Additionally, several FDA-approved drugs inhibit TRK proteins along with cell signaling pathways for which they are better known. Cabozantinib (Cabometyx; Cometriq), a small-molecule inhibitor of multiple receptor tyrosine kinases, targets TRK B along with MET, RET, VEGFR, and FLT3. It is in clinical development for 

Other multikinase inhibitors with the potential to target TRK include the FDA-approved drugs regorafenib (Stivarga), crizotinib (Xalkori), and midostaurin (Rydapt).4 Thus far, clinical trials employing these drugs in 

 fusion-positive cancers have not been announced.

In addition to their promising clinical activity, entrectinib and larotrectinib are noteworthy because of the “tumor agnostic” manner in which they are being developed. Patients are enrolled into clinical trials based on whether their cancer exhibits the biomarker target under study rather than a particular tumor type. Some of the studies have employed basket trial designs that have been growing in popularity as a way to better identify reliable molecular biomarkers that can predict therapeutic response to a drug across tumors with diverse histologic backgrounds.

Despite the inherent challenges associated with the rarity of

fusions, the data emerging from the development of TRK inhibitors support widespread genetic testing for these genomic abnormalities. The novel paradigms being used for the development of TRK inhibitors could make them the most rapid bench-to-bedside success story in the history of targeted therapies.

Based on the striking data presented at ASCO, Loxo Oncology plans to submit a new drug application to the FDA in late 2017 or early 2018.15 If approved, LOXO-101 would follow in the footsteps of pembrolizumab (Keytruda) as the latest option in a new generation of cancer-agnostic drugs for patients with a specific molecular biomarker. Pembrolizumab was recently approved for the treatment of patients with microsatellite instability or mismatch repair defects regardless of tumor type.

The success of kinase inhibitors for treating diverse cancer types has been overshadowed by the development of resistance and TRK inhibitors appear to face the same issue; the duration of response to entrectinib and larotrectinib is likely to be limited by acquired resistance.

Several studies have detailed the acquisition of secondary mutations in the TRK kinase domain following treatment with a TRK inhibitor, similar to the mechanisms of resistance reported for other kinase inhibitors.

Specifically, they include the G595R, G677C, and G623R substitutions that affect the solvent front (so-called because of its biochemical properties) and the xDFG motifs of the kinase domain. These mutations have subsequently been shown to render cancer cells resistant to all TRK inhibitors currently in clinical development.

Learning from past experience, Loxo Oncology is seeking to stay 1 step ahead of the game with a next-generation TRK inhibitor, LOXO-195. A recently published report on the preclinical development of LOXO-195 included data from the first 2 patients treated after developing resistance to larotrectinib.

Both patients experienced a rapid response to LOXO-195. The first patient, an adult with 

 fusion-positive colorectal cancer had a 58% reduction in tumor burden and remains on treatment after more than 6 months. The second patient, a 2-year old with 

 fusion—positive infantile fibrosarcoma, was treated for 3 months. She experienced a partial response, with tumor regression of at least 30%, but eventually succumbed to her disease.

Historically, there has been a significant delay in the development of second-generation drugs, as characterization of the mechanisms of resistance and the subsequent development of drugs to overcome them usually followed FDA approval and substantial clinical experience with the first generation. In this case, researchers already anticipate widespread resistance, and the development of the next generation of TRK inhibitors is occurring simultaneously

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Articles

The growing use of next-generation sequencing has only recently revealed the neurotrophic tropomyosin receptor kinase (NTRK) gene presence across a wide range of tumor types and piqued interest in their potential as anticancer targets.

TRK Inhibitors Advance Rapidly in "Tumor-Agnostic" Paradigm

An analysis of the genomic landscape of patients with prostate cancer shows that tumors separated into 3 clusters that aligned with the luminal A, luminal B, and basal subtypes found in breast cancer tumors, according to a presentation during the 2017 American Urological Association Annual Meeting.

A comparison of the genomic risk profiles of patients with low-risk prostate cancer who are candidates for active surveillance against higher-risk patients, which was completed in order to characterize the genomics of clinically low-risk prostate cancer, discovered that substantial genomic heterogeneity exists among patients with prostate cancer.

“Most low-risk prostate cancers have a clear guideline statement that [they] should be managed with active surveillance. Yet, we know that some low-risk tumors are undersampled at diagnosis, that there’s a small proportion of clinically low-risk tumors that will progress quickly, and [that] there are a larger proportion of these tumors that are entirely indolent and never show any signs of growth over the patient’s lifetime,” said Matthew R. Cooperberg, MD, MPH, associate professor of urology and Helen Diller Family Chair in Urology at the University of California, San Francisco (UCSF) School of Medicine.

Although there are several emerging biomarkers that help classify and determine the prognosis of patients with prostate cancer, some of which are already in clinical practice, they typically reflect only 1 or a few aspects of the overall tumor biology. This study aimed to generate a more comprehensive description of what genomic expression looks like in clinically low-risk prostate cancer to determine which patients are good candidates for active surveillance.

The study considered 408 biopsies from a cohort of patients in the UCSF urologic oncology database who were considered potentially suitable for active surveillance. These patients had Gleason 3+3, low-volume 3+4, stage ≤T2N0M0 disease, or a prostate-specific antigen (PSA) score ≤10 ng/mL. The biopsy samples were profiled by GenomeDx Biosciences using the Affymetrix human exon microarray to generate RNA expression data. These patients had also undergone surgery, so their pathologic outcomes were made available to the investigators.

The biopsies were compared with nearly 1300 cases in the GenomeDx database, which had been previously profiled for clinical decision making; most of the patients had higher-risk features. Their UCSF Cancer of the Prostate Risk Assessment (CAPRA) risk profile was assessed using a point system, looking at the patient’s age at diagnosis (younger or older than 50 years), PSA at diagnosis, Gleason score of the biopsy (primary/secondary), clinical stage, and percent of the biopsy cores with cancer (less or more than 34%).

 Based on the CAPRA score, 75.5% of patients were classified as low risk (score 0-2) and 22.5% were intermediate risk (score 3-5); the reference specimens were mostly higher risk.

Based on 21 prognostic signature risk models, patients were divided into quartiles. Fifty-four percent of patients were in the first quartile, 26% in the second, 15% in the third, and 5% in the fourth. Cooperberg noted that several of the low-risk patients were included in the third and fourth quartiles.

Compared with previous research of other genomic risk scores, the results of the study were consistent with most of the previously published risk scores, according to Cooperberg, with highrisk patients, in particular, lining up with previous research. “The interesting thing is, if we look at the individual pathways, we see a tremendous amount of heterogeneities, so it is not the case that highrisk [disease] is being consistently driven by only 1 or a few pathways,” he commented.

When narrowing the analysis down to only those patients who were Gleason 3+3, Cooperberg noted that there are many patients who have very aggressive genomic expression. In an unsupervised cluster analysis, allowing for the factoring of the different genomic pathways regardless of any previously published risk algorithm, 3 distinct clusters of genomic expressions emerged, “agnostic to any previously described standard clinical risk assessment,” he said.

Notably, these 3 clusters Cooperberg and his colleagues classified as luminal A, luminal B, and basal subtypes, similar to breast cancer tumors, according to PAM50 testing criteria. “We found patterns that look very much like these breast cancer expression patterns, and we’ve seen similar patterns now in bladder cancer as well,” Cooperberg said.

When digging further into these subtypes, researchers found they do not necessarily function as prognostic signifiers, but there is a distinct biology driving the different tumors, Cooperberg noted. Among Cluster 2, the luminal B-like tumors, these tumors had a slightly higher tumor volume and lower PSAs, whereas Cluster 3, the luminal A-like tumors, had slightly lower tumor volume and higher PSAs (Table). According to Cooperberg, these subtypes seem to be driven by androgen response elements in particular. However, he noted that there were no major differences in the clinical risk stratification between these subtypes.

Table. Characteristics of Prostate Cancer Clusters

These classifications in prostate cancer are in line with breast cancer subtypes, as was recently acknowledged in a paper published in 

 This study found further associations with these subtypes, including increased androgen receptor expression in both luminal subtypes. There was an association with poor outcomes among those with luminal B-like prostate cancer compared with the other subtypes.

“We found substantial—and frankly, somewhat surprising&mdash;genomic diversity among these cancers, which clinically, histologically, and pathologically have always looked homogenous. I think the prostate cancer cases we are currently seeing across different cohort studies classify in ways that, in many respects, look like other cancer types,” Cooperberg said.

This research, including Cooperberg’s conclusions for this study, may be building toward a clinical molecular taxonomy for cancer that goes beyond the organ of origin to a more biologic description of why the cancer originated and how best to treat it. This could help drive further improvements in management decision making, both in terms of who should be treated and how treating urologists can tailor therapy and surveillance protocols.

Cooperberg MR, Erho N, Chan JM, et al. The diverse genomic landscape of low-risk prostate cancer. Abstract presented at: 2017 American Urological Association Annual Meeting; May 12-16, 2017; Boston, MA. Abstract PNFBA-09. jurology.com/article/S0022-5347(17)34704-3/pdf.

Prostate cancer risk assessment and the UCSF-CAPRA score. UCSF Department of Urology. urology.ucsf.edu/research/cancer/prostate-cancer-risk-assessment-and-the-ucsf-capra-score. Accessed July 7, 2017.

Zhao SG, Chang SL, Erho N, et al. Associations of luminal and basal subtyping of prostate cancer with prognosis and response to androgen deprivation therapy [published online May 11, 2017]. 

A comparison of the genomic risk profiles of patients with low-risk prostate cancer who are candidates for active surveillance against higher-risk patients, discovered that substantial genomic heterogeneity exists among patients with prostate cancer.

Genomic Landscape of Prostate Cancer Aligns With Breast Cancer Subtypes

James F. Holland, MD, stumbled into the field of oncology by chance. As a captain in the Army Medical Corps during the Korean War, he was preparing to head home from Europe and return to his third year of residency at Columbia University College of Physicians and Surgeons. But when President Harry S. Truman authorized an extension, Holland had to write a letter to Robert F. Loeb, MD, then a professor of medicine at the institution, informing him that he wouldn’t be back to school. Loeb couldn’t hold his spot, but instead offered him a position at Frances Delafield Hospital, then at Columbia University Medical Center in New York. “I’ll call you back when somebody gets tuberculosis or a psychiatric disorder,” his mentor told Holland. “They always do.” 

But after being thrown into oncology care when he treated a 4-year-old with acute leukemia named Jennifer—a chapter that Holland calls “a dramatic part” of his life&mdash;Holland had a different answer when Loeb called him back to practice general medicine. “I said, ‘Thank you, Dr Loeb, but I think I’ll stay,’” Holland recalled.

Holland, of course, did more than just stay in the oncology field. In a career that has spanned more than 60 years, Holland has emerged as a groundbreaking and prolific researcher in developing combination chemotherapies for patients with leukemias. Today, the 92-year-old researcher and physician is the Distinguished Professor of Neoplastic Diseases at the Icahn School of Medicine at Mount Sinai in New York City. 

The choice of specialty was not the only time that Holland’s path could have veered away from oncology. In fact, he could have gone in an entirely different career direction. When he was attending Princeton University in the 1940s, he was also interested in becoming a lawyer. “My father was a lawyer,” said the Morristown, New Jersey, native. “But I had a wonderful biology teacher at Princeton, and I found some of the information that I learned and the way it was taught to be of great interest. Therefore, I chose medicine rather than the law. A good teacher really can inspire.”

Another occurrence that made a significant impact on Holland was his young patient Jennifer, whom he treated as an assistant attending physician at Frances Delafield Hospital. “Unhappily, she died,” he said. “I remember distinctly the great trauma to her mother, father, and to me, when this child relapsed.”

But this hospital also was where he met one of his lifelong mentors, the late Alfred Gellhorn, MD. They bonded after Gellhorn reviewed a thesis that Holland had written on the prostate, which followed the findings of Charles B. Huggins, MD, postulating that castration could be used as a treatment for prostate cancer.

It wasn’t long before Holland was offered a senior attending physician position in 1953 at the National Cancer Institute (NCI) in Bethesda, Maryland, a “terrific experience” that he also credits Gellhorn for granting him. “The National Institutes of Health is a paradise for people who are interested in science and investigation,” said Holland. “It was challenging and tremendous. I learned a great deal there, and I was very happy.”

At the NCI, Holland was the first researcher to put 2 drugs together for patients with acute leukemia. “When I went to the NCI, I was lucky to be assigned to help a major league scientist, Dr Lloyd Law. He was the first man to [combine] 2 drugs in treating chemotherapy in mice, and he showed that if you used drug A or drug B together, the outcome was better.”

After Holland left the NCI for a position at Roswell Park Cancer Institute in 1954, Emil Frei III, MD, continued his research at NCI. They started a significant collaboration: the first inter-institutional program involving chemotherapy as cancer therapy.

Joseph H. Burchenal, MD, became chairman of Acute Leukemia Group A, while Frei and Holland shared the chairmanship of Acute Leukemia Group B for 33 years. As the group expanded, Holland changed the name to Cancer and Leukemia Group B, which has since morphed into its current name, Alliance for Clinical Trials in Oncology (ACTION).

Also as a result of this collaboration, Holland said he and Frei became “brothers joined at the hip,” so much so that they published a book together, 

, described as a respected reference source for medical oncologists, radiation oncologists, internists, surgical oncologists, and others who treat patients with cancer. The ninth edition was issued earlier this year.

“I’m very satisfied with the way things are evolving,” said Holland. “We have changed the concept of cancer from guaranteed death to curing a lot of people. Many oncologists have used this as their educational basis for learning about cancer. That’s been a great satisfaction—having trained a lot of people and treated a lot of patients, many of whom are cured.”

In addition to guiding the field through his writing, Holland has served in leadership roles in the most prominent oncology groups, including as president of the American Association for Cancer Research, president of the American Society of Clinical Oncology, and scientific adviser to the NCI, the World Health Organization, and the African Organization for Research and Training in Cancer. He was a special consultant for a cancer research initiative in the Soviet Union (then the USSR) from 1972 to 1973. He also has served as the scientific director of the T.J. Martell Foundation for Leukemia, Cancer and AIDS Research.

Throughout his career, Holland has been part of many game-changing endeavors, including the development of the POMP chemotherapy combination of mercaptopurine (Purinethol), vincristine (Oncovin), methotrexate, and prednisone for children with acute lymphoblastic leukemia. He has also constructed the 7 + 3 regimen for administering cytarabine and daunorubicin as treatment for adults with acute myeloid leukemia, and he identified cisplatin for the treatment of patients with testicular cancer and doxorubicin for individuals with osteosarcoma.

Today, Holland is at Mount Sinai Medical Center, where he has been since 1973. He started as the director of the cancer center there, prior to the founding of Tisch Cancer Institute. The institution, he adds, is a constellation of people of extremely high caliber. “I have had lots of friends here who are very well specialized in particular areas, such as gynecology, infectious disease, neurology, and cardiology,” he said. “My stay at Mount Sinai has been extremely interesting, provocative, and helpful.”

He still treats patients, albeit on a reduced schedule. “I don’t see as many as I used to see, and I don’t walk as far I used to walk,” said Holland, alluding to his age. “I’m an old man. But I still see patients. I deplore some of the acts and circumstances of what would be called ‘modern computer docs.’ They spend time looking at a computer, not the patient. That’s not the kind of medicine I practice.”

Aside from time spent on applying for grant funding for cancer research, Holland has also been actively studying with a virologist to explore a viral cause of human breast cancer. Thus far, evidence suggests that the human mammary tumor virus may be a causal agent for the disease.

“We found it,” says Holland, adding there is much in oncology still unknown. “Forty percent of American women’s breast cancers contain this virus. It is there before the breast cancer develops; it’s in the milk and probably infects the boys and girls who nurse. Eight percent of American women have it in their milk, and that is enough to account for the viral breast cancer. The overall community does not accept it, but before I die, we will prove that it is the case for 40% of American women’s breast cancers, which would change the entire field. This is because we would have to identify who those 40% are and, potentially, who are the ones who are going to get breast cancer because they got the virus when they were infants and nursing.”

In his nearly 70 years of practicing medicine, Holland has seen quite a bit of change. For example, he has seen the demand for his field increase. At Frances Delafield Hospital, his salary was $4000 annually; that figure jumped to $7600 at the NCI and then again to $11,600 at Roswell Park Cancer Institute. “Those were fortunes of dollars in those days,” he said.

Money aside, the explosion of interest in immunology is “wonderful,” he observed. “I have been interested in it for many years, and I worked on [research] that turned out to be partially successful,” he said. “Now, people have recognized more intensely the impact of immunologic defense and the role of the T cell, which now can destroy tumors and which we suspected, but didn’t know.”

With the addition of monoclonal antibodies including the PD-1/PD-L1 checkpoint inhibitors, researchers are learning how to activate the body’s own defenses. “Activating all of the understandable components of the immune system, of which we don’t know a great deal about, is likely to become the future of oncology, and it’s nontoxic because they are T cells that you already have. Can they cause troubles? Sure. Are there side effects? You bet. Nothing is for free.”

Holland noted that radiation therapy, surgery, and chemotherapy all have downsides that people should take into consideration. “Science is really an extraordinary, romantic, wonderful area in which to work, in which to learn,” Holland reflected. “In medicine, every patient who walks in the door is really an experiment. You shouldn’t [treat anyone] and take it for granted because there are so many potential opportunities to make a wrong diagnosis as well as the satisfaction of making the right diagnosis and proper treatment. It has been very rewarding.” 

Although he may not have a favorite philosphical maxim, Holland says there is a phrase he does always repeat. “I say ‘I love you’ to my wife. We’ve been married 61 years,” said Holland, whose wife is Jimmie C. Holland, MD, the Wayne E. Chapman Chair in Psychiatric Oncology at Memorial Sloan Kettering Cancer Center. Jimmie Holland is the 2014 

 winner in the Supportive Care category. The couple, who met while Jimmie Holland was visiting a friend in Buffalo, New York, have 6 children together.

“We have a lot of common interests,” Holland reflected. “The marriage is highly successful not because she is interested in oncology; it is because of who she is. Life has been very good to me.”

Holland, who calls himself a workaholic but spends downtime with his children and grandchildren, remembers one other phase he does keep in mind. “I suppose my one saying is, ‘Nobody’s got a round-trip ticket. It’s a one-way ticket.’ I’m prepared for when the time comes. I don’t want to leave, but I’m not afraid of death. I recognize that I’ve been very lucky in life. I’ve had lots of rewards, satisfactions, and opportunities to do things.”

James F. Holland, MD, reminisces on nearly 70 years of practicing medicine.

Writing the Book on Cancer Care: Holland Reminisces

Selinexor (KPT-330), a small-molecule inhibitor with a novel mechanism of action, is being investigated in patients with multiple myeloma (MM) who have become refractory to the many new options that have been introduced in recent years for patients with the malignancy.

The drug, which targets the chromosomal maintenance protein exportin-1 (XPO1), is being administered in combination with low-dose dexamethasone to treat patients with MM who are refractory to 4 therapies (quad-refractory) or to 5 treatments (penta-refractory) in the single-arm phase II STORM trial (NCT02336815). In this study, refractory is defined as a ≤25% response to therapy, progression during therapy, or progression within 60 days after completion of therapy. There is no upper limit on the number of prior therapies the patient can receive before enrollment. Eligible patients will have active (versus smoldering) MM. Quadrefractory is defined as patients who have stopped responding to the MM backbone therapies of lenalidomide (Revlimid), pomalidomide (Pomalyst), bortezomib (Velcade), and carfilzomib (Kyprolis). Pentarefractory refers to patients who no longer respond to those drugs plus daratumumab (Darzalex), an anti-CD38 monoclonal antibody.

The trial is divided into 2 parts: part 1 is composed of patients with quad- and penta- refractory MM, while part 2 will consist of individuals with pentarefractory disease. The study has completed enrollment of 79 patients for the part 1 cohort; an additional 122 patients are being recruited for part 2. (Figure).

Figure. Selinexor in Refractory Multiple Myeloma

Selinexor inhibits XPO1, a nuclear export protein, by binding to other proteins within the nucleus of the cell and shuttling them through the nuclear pores into the cytoplasm in the rest of the cell. “For reasons that are definitely advantageous in terms of cancer treatment, XPO1 is the carrier for the vast majority of tumor suppressor proteins that keep cancer cells from growing,” said Dan T. Vogl, MD, assistant professor of medicine in the Hematologic Malignancies and Bone Marrow Transplant programs at the Abramson Cancer Center of the University of Pennsylvania and a leading investigator for the STORM trial.

By blocking the export process, selinexor enables tumor suppressor proteins to remain in the cell nucleus and promote apoptosis. Additionally, selinexor inhibits XPO1 from exporting the glucocorticoid receptor to which corticosteroids bind.

“By keeping the glucocorticoid receptor in the nucleus, it potentiates the effects of steroids in the cell, and since in multiple myeloma corticosteroids can induce a response by themselves, the selinexor and the dexamethasone are working synergistically, with the selinexor having its own effect through other tumor suppressor proteins that it’s keeping in the nucleus, but then also potentiating the effect of the dexamethasone,” Vogl said.

Vogl said selinexor provides a unique method for attacking cancer. “The most attractive thing about selinexor is that it has a novel mechanism of action. I don’t think there is any drug that targets the nuclear export system, and so it’s a completely new way to think about targeting cancer cells,” he said. “Its efficacy is theoretically not restricted to multiple myeloma, but could potentially have preclinical efficacy in a broad range of tumor models.”

For the STORM trial, investigators predicted that the response rate to dexamethasone as monotherapy in patients with penta-refractory MM would be 0% and that the response rate to any other treatment would be less than 20%. In this patient population, an overall response rate (ORR) of 15% to 20% or greater would be significant. “If you can get a response in at least 1 of 5 people, that’s clinically meaningful, and it would be good to have new agents with new mechanisms of action that had that efficacy,” Vogl said.

The most common adverse events (AEs) experienced with selinexor are fatigue, anorexia, nausea, and vomiting. Other AEs seen in past trials have included low blood counts, primarily thrombocytopenia, and to some extent neutropenia, anemia, and hyponatremia. The STORM study has a proactive symptom management regimen to help counteract these AEs, Vogl said.

Selinexor has demonstrated positive responses in heavily pretreated patients with MM. Preliminary results were reported at the 2016 American Society of Hematology Annual Meeting for 48 quadrefractory and 31 penta-refractory patients initially enrolled in the study. One patient did not have measurable disease, so 78 patients were evaluable for efficacy. The ORR was 20.5% among the entire patient population, with an ORR of 20.8% for quad-refractory patients and 20% for pentarefractory patients.

The results marked the first report of antitumor activity in penta-refractory MM, investigators said in their abstract.

 “I think that if we can demonstrate a robust response rate in the 20% to 30% range and show that the responses continue to look clinically meaningful, this would then place selinexor and dexamethasone as a treatment option, especially for patients who don’t have any other available treatments,” said Vogl.

Selinexor is among several novel compounds using SINE (selective inhibitor of nuclear export) technology developed by Karyopharm Therapeutics, based in Newton, Massachusetts, which is sponsoring the STORM trial.

Vogl DT, Dingli D, Cornell RF, et al. Selinexor and low dose dexamethasone (Sd) in patients with lenalidomide, pomalidomide, bortezomib, carfilzomib and anti-CD38 Ab refractory multiple myeloma (MM): STORM study. 

 2016;128(22):491. bloodjournal.org/content/128/22/491?sso-checked=true.

Selinexor (KPT-330), a small-molecule inhibitor with a novel mechanism of action, is being investigated in patients with multiple myeloma who have become refractory to the many new options that have been introduced in recent years for patients with the malignancy.

XPO1 Inhibitor Offers Novel Mechanism for Treating Penta-Refractory Myeloma

The FDA’s recent approval of 2 immunotherapies for the treatment of certain patients with tumors that exhibit microsatellite instability (MSI) has propelled the emerging biomarker into clinical practice, prompting calls for broader genetic testing. The body of research into the optimal use of MSI testing is growing, and clinicians will no doubt encounter evolving data about its clinical utility.

In May, the FDA granted accelerated approval for pembrolizumab (Keytruda) for the treatment of adult and pediatric patients with unresectable or metastatic MSI-H or deficient mismatch repair (dMMR) refractory solid tumors for whom there are no alternative treatment options, and for patients with MSI-H or dMMR colorectal cancer (CRC) who are resistant to fluoropyrimidine, oxaliplatin, and irinotecan. In August, nivolumab (Opdivo) gained an accelerated approval for adult and pediatric patients with MSI-H or dMMR metastatic CRC (mCRC) that has progressed after standard chemotherapy.

Microsatellites, or tandem repeats of short DNA sequences, are abundant throughout the genome.

 Tumors can develop along the MSI pathway, which is driven by a defective MMR mechanism, explained Zsofia K. Stadler, MD, a medical oncologist at Memorial Sloan Kettering Cancer Center (MSK) in New York City. “Their DNA is mismatched but it is not fixed,” she said in an interview with 

. “Therefore, throughout the entire tumor genome, you get the introduction of small point mutations within the tumors; these are called microsatellites. These essentially become unstable in these tumors, which is MSI.”

Although MSI testing has become an established part of the workup for patients with CRC, researchers are increasingly finding that MSI plays a role in other tumor types. “MSI may occur in a broad spectrum of tumors,” said Antonia R. Sepulveda, MD, PhD, a professor of pathology and cell biology and vice chair for translational research at Columbia University in New York City, in an interview. She noted that, in patients with Lynch syndrome, MSI may be a factor in endometrial, ovarian, skin, brain, and upper gastrointestinal tumors.

“Then there are sporadic types of MSI tumors. In every tumor type, they’re going to be of much lower frequency,” she said. “For example, we’ll find MSI tumors in prostate cancers and bladder cancers, but very infrequently in other cancers, like sarcomas. Nonetheless, especially for patients who might have had other risk factors, like previous therapies and/or enhanced exposure to carcinogens, we’re still not clear about what [the MSI rate] might be. Occasionally in lower frequencies, we might find MSI across the board in most tumors.”

In sporadic cases, MSI is caused by inactivation of MMR genes (eg, 

) through somatic mutations, with increased cancer risk in individuals with inherited germline mutations (ie, Lynch syndrome).

, or downregulation of MMR genes by microRNAs can also cause MSI.

 When MSI occurs within coding regions, the reading frame can be altered, resulting in functionally impaired proteins.

Typical tumors may have approximately 100 mutations in the exome; however, MSI-positive CRCs, for example, characteristically have thousands of mutations in the coding regions of tumor cells.

 MSI-positive tumors also have higher numbers of tumor infiltrating lymphocytes (TILs), such as cytotoxic T cells, which is thought to be a result of increased neoantigen production induced by the high mutational load. These neoantigens are recognized as foreign, driving an inflammatory response.

As a compensatory response to this inflammation, MSI-positive tumors upregulate molecules such as the immune checkpoint protein PD-L1, which allows cells to evade the immune system. A phase I study in treatment-refractory MSI-positive tumors reported responses to a PD-1 blockade with pembrolizumab, demonstrating that reversing this inhibitory pathway leads to durable immune-mediated tumor control by reactivating TILs.

MSI can be classified as MSI-high (MSI-H), MSI-low (MSI-L), or microsatellite stable (MSS). Using MSI testing, tumors are identified as MSI-H when 30% or more of the repeats are unstable, as MSI-L if fewer than 30% of the repeats are unstable, and as MSS if no repeats are unstable.

MSI and/or immunohistochemistry (IHC) testing facilitates targeting the gene sequencing of MMR genes and screening out individuals unlikely to have Lynch syndrome.11 MSI testing detects an abnormal number of microsatellite repeats, indicating that cancer likely arose from cells with defective MMR genes. IHC testing detects the presence or absence of protein products of the MMR genes, of which a missing protein suggests a mutation in the gene that codes for that protein.

Polymerase chain reaction—based MSI testing amplifies DNA at several microsatellite sites from a tumor tissue sample and must be compared with normal DNA from each patient.

 MSI testing can profile the Bethesda markers (often 2 mononucleotide and 3 dinucleotide microsatellite loci) or 5 mononucleotide markers as recommended by the National Cancer Institute/International Collaborative Group on Hereditary Non-polyposis Colorectal Cancer (NCI/ICG/HNPCC), but this method is time consuming and expensive.

A recent study evaluated the use of a single mononucleotide marker, CAT25, and reported high specificity and sensitivity for identifying tumors with MMR deficiency; however, this method would need to be evaluated in various ethnic populations to ensure consistent results.14 MSI testing has 80% to 91% sensitivity among tumors with 

 mutations and 55% to 77% sensitivity among 

 Based on the composition of the MSI panel, specificity may reach 90%.

IHC is a complementary testing strategy, wherein most MSI-H tumors demonstrate a loss of protein expression for at least 1 MMR gene. Loss of protein expression within tumors is helpful for identifying the corresponding genes to target for mutation analysis.

 IHC testing has a sensitivity of 83%, regardless of the MMR gene involved, with a specificity of 89%.

 It is convenient, inexpensive, and may detect loss of MSH6 protein that can be missed via MSI testing.

 IHC staining patterns may vary, however, leading to uncertainty in the interpretation of results.

MSI and IHC are often used synergistically to detect cases that may be missed by either test alone; however, they can be used separately based on individual clinical barriers such as cost and specimen availability.

 A recent study demonstrated the equivalence of MSI testing and MMR IHC in a cohort of patients with endometrial carcinomas, supporting previously reported concordance rates of over 92%.

A recent NRG Oncology and Gynecologic Oncology Group Study evaluated the combination of MSI testing, 

 methylation analysis, and IHC in patients with endometrial cancer, identifying patients with Lynch syndrome who would not have been considered for mutation testing if only IHC and MSI were used.

MSI testing is usually ordered at the time of CRC diagnosis to identify patients with Lynch syndrome, to determine prognosis, or to direct adjuvant chemotherapy.

 When asked whether providers should initiate MSI testing at diagnosis, Luis A. Diaz, MD, head of the Division of Solid Tumor Oncology at MSK, said, “That remains to be seen, but I think, right now, anyone with metastatic disease who has progression on standard-of-care therapy should have their MSI-H status checked because it can have a profound impact.”

MSI occurs in approximately 15% of sporadic CRCs in the United States.

 It has also been reported in glioblastomas, lymphomas, and tumors in the stomach, ovaries, endometrium, and urinary tract.

 MSI-prone tumor types include colon adenocarcinoma, esophageal carcinoma, rectal adenocarcinoma, stomach adenocarcinoma, and uterine corpus endometrial carcinoma; these types contained the majority of MSI events in a recent molecular analysis study.

Another recent study evaluated MSI presence and the number of unstable loci in 18 tumor types.

The recent approval of 2 immunotherapies for the treatment of certain patients with tumors that exhibit microsatellite instability has propelled the emerging biomarker into clinical practice, prompting calls for broader genetic testing.

Vol. 18/No. 15 | Oncology Live®

TRK Inhibitors Advance Rapidly in "Tumor-Agnostic" Paradigm

Genomic Landscape of Prostate Cancer Aligns With Breast Cancer Subtypes

Writing the Book on Cancer Care: Holland Reminisces

XPO1 Inhibitor Offers Novel Mechanism for Treating Penta-Refractory Myeloma

Biomarker Basics: A Look at MSI's Growing Role

Sequenced Treatment Making Inroads in HER2-Positive Early Breast Cancer

New Strategy Boosts Microenvironment to Promote Antitumor Immunity in GI Metastases

Missing the Mark: "Clinical Benefit" Is Often an Empty Term