IHC Testing May Bridge Gaps With NGS for Early Identification, Intervention in TP53-Mutant MDS and AML

In an interview with OncLive®, Jonathan M. Gerber, MD, and Shyam A. Patel, MD, PhD, discussed the technological advancements and therapeutic implications of findings from an analysis of immunohistochemistry (IHC) test results as a potential biomarker for TP53 allelic status in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML).

This included the importance of early identification and expedited intervention via stem cell transplant for patients with multi-hit TP53 status; the potential for routine next-generation sequencing (NGS) as multi-institutional efforts continue; and the need for more insight into disease biology given the negative results of recent investigations of targeted therapeutics for TP53 mutations.

“In our own [study], the only long-term remissions or potential cures have occurred in patients with both low [TP53] variant allele frequency [VAF] and low IHC positivity,” Gerber explained in an interview with OncLive®. “IHC may serve as an additional rapid marker to guide early risk stratification and help direct therapeutic decision-making. There are additional nuances that still need to be clarified.”

“If this biomarker can be validated in larger-scale studies and across different institutions, perhaps that would lead to a path toward more expedited stem cell transplant evaluation,” Patel added.

Patel and Gerber expanded on the rationale, design, and primary findings from this analysis in a concurrent interview.

Gerber is a member of the faculty in the Department of Medicine at New York University (NYU) Grossman School of Medicine, as well as the chief clinical officer of the NYU Perlmutter Cancer Center. Patel is an associate professor at the University of Massachusetts Chan Medical School, as well as a hematologist and oncologist at the UMass Memorial Medical Center in Worcester.

OncLive: How should clinicians interpret a negative IHC result in the context of suspected TP53-altered disease?

Patel: [This] suggests that the IHC results have a relatively low sensitivity but a higher specificity; it suggests that this test could be a good rule-in test, but not necessarily a rule-out test because in some cases, we might miss patients who have a nonsense frameshift [mutation] or 17p deletion [del 17p], so a clinician might not want to conclude that a patient has wild-type TP53 based on a negative test, if they ended up having a nonsense frameshift mutation or del 17p, because there is a chance of a false negative result. In those cases, the clinician may want to wait for the full NGS results to come back.

However, in the case of at least 1 missense mutation, we almost always found that the IHC was positive; whereas, if there was no missense mutation, there were a good number of cases that were false negatives or missed. Therefore, we have to interpret this in the right clinical context

Gerber: We performed a detailed codon-level analysis to evaluate the correlation between TP53 IHC and NGS, and we observed that negative IHC results were sometimes seen in patients with nonsense mutations, frameshift mutations, del 17p, or isochromosome 17q. [These findings] suggest that IHC results had a relatively low sensitivity but a higher specificity. They suggest that this test could be a good rule-in test, but not necessarily a rule-out test, because in some cases, we might miss patients who actually have a nonsense mutation, frameshift mutation, or del 17p mutation. A clinician might not want to conclude that a patient has wild-type TP53 based on a negative [IHC] test [in this case], because there is a chance of a false negative result. In such scenarios, clinicians should consider awaiting full NGS results before making definitive treatment decisions.

However, in cases where at least 1 missense mutation was present, the IHC result was almost always positive. If there was solely a nonsense mutation, del 17p, or isochromosome 17q, there was a substantial proportion of false-negative IHC results. [These data underscore] that we have to interpret [test results] in the right clinical context.

What is the significance of the observed inverse correlation between p53 IHC positivity and overall survival (OS), particularly in the highest staining quintile?

Patel: In terms of the relationship between IHC and OS, we did find that IHC positivity correlated with inverse OS [outcomes]. Specifically, we performed a subgroup analysis based on IHC quintiles and observed an inverse correlation with median OS. The clinical implication is that this information can provide early insight into survival statistics, and IHC could serve as a useful early biomarker to guide discussions about prognostication.

For example, if a patient was found to have an IHC positivity of 80%, their median OS based on our study was approximately 2.5 months. [In contrast], if a patient had an IHC positivity of only 20%, their median OS was as long as 8 months. The field may benefit from larger-scale studies or multi-institutional analyses for biomarker validation of IHC in patients with TP53-mutant MDS or AML.

Gerber: Those are pretty humbling survival numbers. The only survival rates that start to look more favorable are in patients with IHC positivity in the single-digit percent range. It’s quite striking. This appears equivalent to looking at cases with VAF less than 20% on NGS. One of the other interesting [considerations is that] not all TP53 mutations are created equal. Certainly, if there is any preserved wild-type function, there is a sense that those patients may do better. We are starting to examine some of those outlier cases to better understand how we might further [stratify] patients or distinguish [prognostic subgroups].

Our dataset was relatively limited. It’s one of the largest in this space for TP53-mutant disease, but it still includes fewer than 150 patients. As we begin comparing data across centers and [delve into] some of the nuances of individual mutations, we may develop a more refined understanding. We also attempted to evaluate whether there was any clinically meaningful disparity between IHC and VAF. Our numbers probably weren't large enough to tease that out, but we do know from other published data that isolated deletions of TP53 with preservation of one wild-type allele do not confer the same adverse clinical impact as TP53 mutations—particularly missense mutations or biallelic inactivation.

What still needs to be learned about the use of p53 IHC as an early biomarker for TP53 mutation status? Are any next steps planned to validate this?

Patel: One consideration within the field of stem cell transplant might be the consideration of expedited stem cell transplant for patients who have multi-hit TP53 mutations. As Dr Gerber mentioned, stem cell transplant is thought to be the main curative-intent option for these patients. Early identification of patients who have multi-hit TP53 or biallelic TP53 status would benefit from that more expedited evaluation.

There have been a variety of studies that have looked at larger-scale cohorts for transplant outcomes for TP53-mutant MDS or AML. The key might be to have these patients proceed with stem cell transplant [as quickly as possible] if they are eligible.

Gerber: Being able to make these decisions is particularly important in patients with AML, where there is often a sense of urgency around initiating treatment. TP53 mutations are more commonly observed in lower white blood cell count AML and MDS, where there is sometimes a bit more time to make treatment decisions. However, these mutations can also present in more aggressive cases with high white blood cell counts and a truly urgent or emergent need for therapy. The earlier we can obtain molecular data, the better we can customize or personalize therapy for each patient.

Planning for allogeneic stem cell transplant [allo-SCT] or other interventions requires lead time. Even when we have temporary disease control—for example, with a hypomethylating agent–based regimen—the transplant window is often narrow. There appears to be a survival benefit with transplant across the board, even in the most high-risk cases, where cure is rare. In many of those cases, patients still experience a prolongation of life. Early identification of high-risk disease, therefore, seems to be our best overall strategy.

How do you envision the implementation of p53 IHC testing in global regions with limited access to NGS, and what are the implications for expanding molecularly guided care in MDS and AML?

Patel: Some of the next questions that we may want to think about as a field would be: are there any antibody subtypes or methodologies that can lead to increased sensitivity for IHC for detecting the actual p53 mutation?

The other aspect is the global cost savings. In many low- and middle-income countries, there might not be ready access to NGS testing, and they may rely on more general, basic histopathological techniques like immunohistochemistry for determining disease designation. It’s possible that IHC potentially could be valuable to low- and middle-income countries that don’t have the ability or the funds to perform NGS testing. It might be worth considering commercializing this if there was validation of this test from a multi-institutional perspective.

Gerber: Even within the United States, in some of our more underserved and rural areas where there might not be ready access both to the expertise with NGS and NGS testing [itself], this is a relatively simple, straightforward assay. Most pathology labs should be capable of performing this if they have the reagents. Hopefully, this can expedite early referral and facilitate early referral to transplant-capable centers, etc.

The other piece of this is that we're fortunate to have expert hematopathologists reviewing these slides and are familiar with the assays. There are certainly some opportunities, as technology is improving, [namely] artificial intelligence, to automate the process, speed it up, and standardize it.

It's a complementary piece of information. In some ways, you get some insight into the function of the protein that we don’t always get from NGS. We imply functional consequences from that, but if the protein abnormally localizes or if the staining is more intense, it [lets us know] that this is a mutation that is actually disrupting wild-type [TP53] function.

In terms of therapeutic implications, the ability to get an answer earlier and actually be able to contemplate clinical trials, screen patients as early as possible, and even look at upfront clinical trial options for them is a critical [unmet need in MDS and AML] and related diseases.

We haven’t had a lot of success yet in developing therapies that are effective against mutant TP53, especially in those with higher allele burdens. This [study] at least gives us some hope that we might be able to delegate patients into trials as early as possible and give them the best chance that we might have for survival and use these [tools] to better understand who may benefit from a given trial.

Patel: These are all very excellent points from the translational perspective. We've seen a lot of negative trials in the literature for targeted therapeutics for TP53, or at least therapeutics that might work against that particular subset. For example, we've seen overall negative results for the [phase 3] ENHANCE-2 [NCT04778397] and ENHANCE-3 [NCT05079230] trials, as well as a few other targeted therapeutics like eprenetapopt [APR‐246] and sabatolimab [MBG453], which have been suspected to be involved in TP53-mutant MDS and AML.

At the current time, there still remains a major pressing need for more insight into disease biology for this particular patient subset. [The more knowledge we have], the more likely we can validate targets that may be amenable to targeting. With more multi-institutional or collaborative efforts across various investigators, hopefully we can try to move the field forward.

How could expanded use of NGS and other technological advances contribute to earlier identification and risk stratification of patients with clonal hematopoiesis or pre-leukemic conditions?

Gerber: Inevitably, we're going to see technology get to the point where next-generation sequencing is faster and used earlier, with more widespread use, including outside of hematology and oncology. We're already starting to see that in other fields, as we understand clonal hematopoiesis better and start to get a sense of the evolution of these diseases. We may eventually have really early data on these mutations and how they're arising.

In prior work that we've done, we found that patients with clonal hematopoiesis, not yet meeting criteria for or having advanced to MDS or AML a, but with these preceding conditions, those who had TP53 mutations, other than maybe a rare patient who had a transient finding, an artifact, or a small clone that wasn’t at the stem cell level and burned itself out, anyone with a sustained TP53 mutation never behaved indolently. They all advanced to either MDS or AML.

Potentially catching these patients as early as we can is key. I'm not suggesting we do bone marrow biopsies and IHC on all of them. Right now, IHC is a great bridge; as Dr. Patel mentioned, in underserved areas, it's a potentially useful option. However, I can envision a time when we're getting routine NGS on people across the board, with much deeper sequencing, including in healthy individuals, and catching these things early. Until such time as we have a better therapy that's effective in those cases, this might be a really good option. As crazy as it sounds, considering a transplant in someone who's otherwise healthy might become a real discussion in the time to come.

Reference

Patel SA, Khedr S, Gordon CD, et al. Early identification of TP53 mutations and TP53 allelic state in myelodysplastic neoplasms and acute myeloid leukemia via point-of-care p53 immunohistochemistry. Cancer. 2025;131(13):e35950. doi:10.1002/cncr.35950