Joseph A. Sparano, MD, associate director for clinical research, Albert Einstein Cancer Center, professor of Medicine & Obstetrics, Gynecology, and Women’s Health at the Albert Einstein College of Medicine, and associate chairman for Clinical Research in the Department of Oncology at Montefiore Medical Center, discusses the utility of liquid biopsies in breast cancer.

In breast cancer, liquid biopsies have limited utility, says Sparano. However, they have shown promise in identifying women who have metastatic estrogen receptor—positive breast cancer and 

 mutations. One of the advantages of liquid biopsies is convenience. With further validation, liquid biopsies could become available in the near future, says Sparano.

Liquid biopsies could also be used to test for 

 mutations to identify patients who have acquired resistance to aromatase inhibitors. Such information is prognostic and potentially predictive of response to more effective treatment with selective ER downregulators, concludes Sparano.

Videos

Dr. Sparano on the Utility of Liquid Biopsies in Breast Cancer

Blood-based biomarkers great potential for use in the management of breast and other cancers. Critical elements in clinical application include analytic validity and clinical validity, which would be required to ultimately establish clinical utility—a biomarker-directed treatment change that results in clinical benefit.

Currently available biomarker assays for breast cancer include circulating protein markers (eg, CA 27.29, CA 15-3), circulating tumor cells (CTCs), and circulating tumor DNA (ctDNA). Other potential biomarkers, collectively referred to as liquid biopsies, include exosomes, microRNA, noncoding RNAs, and tumor-educated platelets.

 The Blood Profiling Atlas in Cancer is an initiative including academic, government, biotechnology, diagnostic, and pharmaceutical institutions to coordinate, harmonize, and collaborate with the goal of moving these technologies into routine clinical care.

CTCs are shed from the tumor and into the bloodstream, where a small percentage survive, extravasate, and colonize distant sites, ultimately developing clinical evidence of metastasis, in some cases after a period of tumor dormancy.

It is estimated that only 1 in 10 million tumor cells from a primary tumor will reach the blood- stream, accounting for only 1 in 10,000 nucleated cells per milliliter of blood,

 with a short half-life of less than 3 hours.

CTCs were first noted in cancer by Thomas Ashworth in 1869.

 Since this seminal observa- tion and the first isolation of CTCs from a blood sample reported in 1955,

 over 50 assays have been reported using different techniques for CTC identification, enumeration, and, in some cases, molecular characterization. Cleared, analytically validated assay that facilitates microscopy-based detection and enumeration of CTCs in metastatic breast, colorectal, and prostate cancers using immunomagnetic beads for positive selection of CTCs expressing epithelium-specific cell adhesion molecule, a positive selection method.

This review will focus on the use of this assay, the CellSearch System (Menarini Silicon Biosystems, Inc; Bologna, Italy), in early and advanced breast cancer. Some of the key conclusions regarding research conducted to date and potential future ap- plications are summarized in the Table.

CTCs are detectable in approximately 65% or more of patients with metastatic breast cancer (MBC), and a CTC count ≥5 cells per 7.5 mL of blood in MBC is associated with significantly inferior progression-free survival (PFS) and overall survival (OS),

 providing evidence for clinical validity. However, prospective randomized trials have not established clinical utility, as described below.

SWOG S0500 (NCT00382018) was a prospective clinical trial including 595 patients with MBC receiving first-line chemotherapy in whom systemic chemotherapy was changed for those with persistently high CTC counts (≥5/7.5 mL blood) after 3 weeks of first-line chemotherapy. The trial failed to meet its primary endpoint of demonstrating improved OS in the 21% of trial participants in whom a CTC-guided change in chemotherapy was compared with continuation of the same chemotherapy.

The STIC trial (NCT01710605) was a prospective clinical trial including 778 patients with hormone receptor (HR)—positive, HER2- negative MBC randomly assigned to a clinically driven treatment arm (physician’s choice of hormone therapy or chemotherapy based on clinical factors) or a CTC-driven treatment arm (hormone therapy if CTC <5, chemotherapy if CTC ≥5/7.5 mL blood).

 Patients whose treat- ment was escalated to chemotherapy based on CTC count exhibited a longer PFS than those whose treatment was clinically driven. The median PFS was 10.5 months with hormone therapy in the clinically driven arm for those who had a high CTC count versus 15.5 months with chemotherapy in the CTC-driven arm and showed a trend toward longer OS (median, 37.1 vs 42.0 months, respectively). Major limitations of the trial included lack of standardized clinical criteria for recommending chemotherapy in the clinically driven arm and the fact that it was conducted prior to the widespread use of CDK4/6 inhibitors, now regarded as the standard of care for HR—positive MBC.

The EORTC 90091-10093 BIG 1—12 “Treat CTC” trial (NCT01548677) was a prospective clinical trial including 63 patients with non-metastatic breast cancer who had detectable CTCs (>1/7.5 mL blood) after neoadjuvant chemotherapy and surgery and who were randomized to trastuzumab (Herceptin) or observation. There was no difference in CTCs at week 18, the trial’s primary endpoint, and the trial was halted for futility.

CTCs in Early Breast Cancer Within 2 Years After Diagnosis

Several other randomized trials are ongoing, as reviewed elsewhere.

 The DETECTIII trial (NCT01619111) is comparing lapatinib (Tykerb) plus chemotherapy or chemotherapy alone in patients with at least 1 CTC with strong HER2 immunocytofluorescence. The CirCe01 trial (NCT01349842) includes patients with MBC and a high CTC count (≥5/7.5 mL blood) about to initiate third-line therapy who are randomized to CTC-directed versus clinically directed change in therapy.

CTCs are detectable in about 20% to 25% of patients with localized nonmetastatic breast cancer at the time of diagnosis and also provide independent prognostic information using a lower threshold (≥1 CTC per 7.5 mL blood) than in MBC (≥5 CTC per 7.5 mL blood), whether obtained before or after surgery, including after neoadjuvant or adjuvant chemotherapy, providing additional evidence for clinical validity.

In a pooled analysis of individual data from 3173 patients with stage I to III breast cancer from 5 institutions, CTCs (>1 per 7.5 mL blood) were detected in 20.2% of patients, and the presence of CTCs was an independent prognostic fac- tor for inferior disease-free survival (DFS; haz- ard ratio, 1.82; 95% CI, 1.47-2.26), distant DFS (hazard ratio, 1.89; 95% CI, 1.49-2.40), breast cancer—specific survival (hazard ratio, 2.04; 95% CI, 1.52-2.75), and OS (hazard ratio, 1.97; 95% CI, 1.51-2.59) in a multivariate Cox regression model including tumor size, nodal status, histologic tumor grade, and HR and HER2 status.

In a meta-analysis that included individual patient data from 21 studies in which CTCs were evaluated in 1574 patients before receiving neoadjuvant chemotherapy (NAC) and 1200 patients after NAC and before surgery, CTCs (≥1/7.5 mL blood) were detected in 25.2% of patients before NAC, and a higher CTC number was associated with OS (

 <.001), and locoregional relapse—free interval (

 <.001) but not on pathological complete response. In 861 patients with full data available, adding CTC detection before NAC also added prognostic information in multivariable prognostic models for OS (

SUMMARY OF KEY FINDINGS AND POTENTIAL FUTURE DIRECTIONS FOR CLINICAL APPLICATION OF EPCAM-BASED CTC DETECTION AND ENUMERATION IN METASTATIC AND NONMETASTATIC BREAST CANCER

CTC indicates circulating tumor cell; ctDNA, circulating tumor DNA; EpCAM, epithelial cell adhesion molecule; MBC, metastatic breast cancer.

Figure. Hypothetical Trial Designs for CTCs as an Integral Biomarker for Surveillance to Test Novel Agents to Prevent Late Recurrence in Hormone Receptor—Positive Breast Cancer

CTCs were detected at 2 years in 18% of 1087 patients with stage II to III breast cancer enrolled in the phase III SUCCESS-A trial,

 which was one of the trials in which CTC was found to be prognostic at diagnosis.

 At 2 years, a positive CTC assay was associated with a 3.9-fold higher risk of death and a 2.3-fold higher risk of recurrence in multivariate models that included clinicopathologic features and CTC status at baseline; sensitivity analysis showed this effect only in HER2-negative disease.

Late recurrence 5 or more years after diagnosis accounts for more than one-half of patients with HR-positive breast cancer.

 Factors associated with higher late recurrence risk include positive axillary nodes and primary tumor size >2 cm, and tools such as the CTS5 calculator may provide more precise estimates of late recurrence risk for individual patients.

 In a study including 353 patients with HR—positive, HER2-negative, stage II to III breast cancer treated with adjuvant chemotherapy and endocrine therapy followed up for 4.5 to 7.5 years after diagnosis without evidence of clinical recurrence, CTCs were detectable in 5.1% (median, 1 cell per 7.5 mL blood; range, 1-15 cells per 7.5 mL blood). Moreover, CTC positivity was associated with a 13.1-fold increase in recurrence risk in mul- tivariate analysis adjusted for other prognostic covariates.

 Because imaging was not performed in any of these trials at the time of the positive CTC assay, it is currently unknown what propor- tion of patients who are CTC positive would be found to have clinical evidence of asymptomatic metastatic disease. In a similar analysis of 206 patients enrolled in the SUCCESS-A study with follow-up information and known CTC status at 5 years, 7.8% were CTC positive at 5 years, which was associated with a 6-fold in- crease in recurrence.

There are several potential strategies for establishing the clinical utility of CTC enumeration and/or characterization, including as a surrogate/replacement of or adjunct to diagnostic imaging,

 therapeutic selection, and surveil- lance. Several ongoing trials may shed further light on the clinical utility of CTC-directed therapy. Here we focus on the potential opportunities as a surveillance biomarker.

Evidence-based guidelines recommend surveillance after treatment of localized breast cancer including history, physical examina- tion, and annual mammography.

 Blood- based biomarkers and imaging studies beyond mammography are not recommended in asymptomatic patients, although these recom- mendations are based on trials performed at a time when diagnostic, imaging, and therapeutic options were limited.

 The availability of more effective therapies for MBC, such as immune checkpoint blockade for triple-negative disease

 or novel oral selective estrogen receptor downregulators

 for HR—positive disease, offers potential for early intervention that could ultimately delay or even prevent metastasis.

Recently, the FDA granted regulatory approval for antiandrogenic agents in the treatment of nonmetastatic castration-resistant prostate cancer based on the endpoint of metastasis-free survival in a setting where an integral biomarker (serum prostate specific antigen) was used to select men at high risk for developing metastasis and lacking distant disease based on standard diagnostic imaging.

 This provides a foundation for de- veloping a similar approach for surveillance and treatment of high-risk, nonmetastatic breast cancer, as exemplified by 2 hypothetical trial designs shown in the figure, including a biomarker selection design and a biomarker stratification design, each of which has its own advantages and disadvantages.

 Such future trials should include cross-platform comparison of different CTC methodologies and other biomarkers, including protein-based markers, ctDNA, and exosomes.

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Articles

Blood-based biomarkers offer great potential for use in the management of breast and other cancers.

CTC Surveillance in Early-Stage Breast Cancer: What's Next?

Joseph A. Sparano, MD, associate director for clinical research, Albert Einstein Cancer Center, Montefiore Medical Center, discusses ways to improve the clinical utility of liquid biopsies in breast cancer.

Currently, liquid biopsies are not utilized as much in breast cancer as they are in other solid tumors, says Sparano. In order to improve the clinical utility of this modality, it needs broader application and study as well as the identification of more effective therapies that are linked with a specific biomarker. An example of this is patients with HER2-positive disease responding to anti-HER2—directed therapy such as trastuzumab (Herceptin) and pertuzumab (Perjeta). But researchers need more examples like this, he notes.

Ideally, Sparano adds, a liquid biopsy panel will include a range of targetable mutations and will be able to tell a patient which corresponding therapy they will best respond to. The greater the sum of alterations and therapies, the more likely a liquid biopsy will have clinical utility.

Another potential application for this technology is in the surveillance of patients who are at a high risk for recurrence and using that biomarker to direct therapy to prevent development of metastasis. The FDA has recently recognized metastasis-free survival as a crucial regulatory endpoint to support the approval of a drug.

Joseph A. Sparano, MD, associate director for clinical research, Albert Einstein Cancer Center, Montefiore Medical Center, discusses ways to improve the clinical utility of liquid biopsies in the treatment of patients with breast cancer.

Dr. Sparano on Improving Liquid Biopsies in Breast Cancer

Joseph A. Sparano, MD, associate director for clinical research, Albert Einstein Cancer Center, Montefiore Medical Center, discusses unmet needs in metastatic breast cancer.

This remains an incurable disease, Sparano says, although there have been significant improvements in clinical outcomes over the last few years. For patients with estrogen receptor-positive, HER2-negative disease, the rise of CDK4/6 inhibitors has dramatically changed the management of that setting. These agents haven

Dr. Sparano Discusses Unmet Needs in Metastatic Breast Cancer

Joseph A. Sparano, MD, associate director for clinical research, Albert Einstein Cancer Center, Montefiore Medical Center, discusses the application of liquid biopsies in breast cancer.

He says that while a liquid biopsy has some advantages over the standard tissue biopsy, there are some challenges that remain before it becomes part of routine clinical practice. The biggest challenge is that liquid biopsies have not yet been clinically proven to result in beneficial treatment for patients. While they are useful in detecting the mutational profile of a tumor, there is still work to be done in improving their clinical utility.

There might be some exceptions to that, says Sparano. Liquid biopsies can be useful in detecting 

 mutations, which are frequently found in the blood and usually come as a result of resistance to aromatase inhibition for patients with estrogen receptor-positive disease. Liquid biopsies are also effective in locating circulating tumor DNA.

Joseph A. Sparano, MD

Articles

Dr. Sparano on the Utility of Liquid Biopsies in Breast Cancer

CTC Surveillance in Early-Stage Breast Cancer: What's Next?

Dr. Sparano on Improving Liquid Biopsies in Breast Cancer

Dr. Sparano Discusses Unmet Needs in Metastatic Breast Cancer

Dr. Sparano on Application of Liquid Biopsies in Breast Cancer