Biomarkers are needed to fulfill several important roles in immuno-oncology, both before and after treatment.
With the emergence of new immunotherapeutic agents for treating cancer, there is a growing need for the identification of biomarkers that will allow clinicians to take full advantage of these treatments. Biomarkers are needed to fulfill several important roles in immuno-oncology, both before and after treatment.
Biomarker testing prior to initial treatment is needed to predict both the efficacy and toxicity of a given treatment option in a particular patient. This would allow clinicians to avoid unnecessary ineffective treatments and help alert both the oncologist and patient to possible serious adverse effects (AEs) before they arise so that a management plan can be made. Pretreatment biomarkers can be classified as either prognostic markers that provide information on the future course of the disease, or predictive markers that identify patients likely to respond or suffer severe AEs from a given treatment. A proposed classification system, the Immunoscore, uses two markers (CD8 and CD3) at different places in the tumor as prognostic biomarkers, and is being validated in colon cancer.1
After treatment, biomarkers are needed that will allow accurate measurement of a patient’s response to therapy. Conventional imaging benchmarks for solid tumors, such as the Response Evaluation Criteria in Solid Tumors (RECIST) or the World Health Organization (WHO) criteria, are often not useful for determining responses to immunotherapies. This lack of utility can occur with immuno-oncology treatments that prolong survival without reducing tumor progression, or in cases where lymphocyte infiltration increases tumor size. Post-treatment biomarkers that directly assay immune activation either at the tumor site or in the blood are therefore more useful for monitoring treatment response.
There are several important considerations for the development of clinically relevant biomarkers in immuno-oncology. Given the complexity of interactions between the immune system and tumor cells, it is likely that a number of different biomarkers will need to be tested in tandem to produce an informative profile.2Markers present in peripheral blood and serum are more desirable for ease of serial analysis over the course of a treatment, and the issues of sample processing and storage are crucial to reducing the amount of variability introduced by handling. Moreover, the testing method used must also be accurate, precise, and reproducible enough to allow for comparisons across different laboratories at different times.3The challenges of identifying predictive biomarkers in immunotherapy are illustrated in results from several clinical trials of cell checkpoint inhibitors. Programmed cell death-1 (PD-1) and its ligand, PD-L1, are promising targets of immunotherapies; however, their suitability as predictive biomarkers is still unclear. PD-L1 is expressed in several different cancers, including breast cancer, lung cancer, and melanoma, and is the target of several inhibitors now being developed. However, data presented at the 2014 ASCO Annual Meeting showed that the rate of PD-L1positive cancer cells in a collection of tissue samples was 50% or less in most tumor types examined.4
“PD-1 and PD-L1 markers are not elevated at the same levels across all cancer types, meaning that the effectiveness of the anti-PD-1 immunomodulatory agents may depend on specific elevation levels,” noted one of the study’s authors, Zoran Gatalica, MD, DSc, executive medical director of Caris Life Sciences, a leading biosciences company that provides broad tumor profiling and biomarker analysis for therapeutic associations for non-small cell lung cancer.
“Moreover, immunotherapies are not appropriate for every solid tumor; some tumors are not associated with these specific immune responses. PD-1/PD-L1 status, however, should be evaluated before embarking on clinical trial enrollment, because this analysis can significantly inform the patient recruitment process, and can be done easily and inexpensively via gold-standard immunohistochemistry testing,”5Gatalica stated.Several methods are being used to overcome the limitations of single markers in immunotherapy, including transcriptome analysis, flow cytometry, and protein microarrays. The Immuno-Oncology assay from Response Genetics, another life sciences company engaged in the research and development of clinical diagnostic tests for cancer, is an immune-focused transcriptional assay designed to facilitate biomarker discovery in clinical trials. These technologies allow investigators in clinical trials to monitor many different potential biomarkers simultaneously to increase predictive reliability and to identify informative markers in an unbiased manner.6 In a phase II trial of ipilimumab, an anti-CTLA-4 antibody, investigators used gene expression profiling in pretreatment and post-treatment tumor samples to identify transcriptional profiles associated with clinical activity of the treatment.7High levels of immune-related genes before treatment were correlated with a greater probability of response. Further studies examining this greater pool of immune-related markers may be able to overcome the uncertainty present when a single marker is used.The use of specific antibodies in peripheral blood as predictive biomarkers would be very desirable in the clinical setting. Blood samples are easy to collect and store, and multiple samples can be taken over the course of a treatment. Protein microarrays have proven to be a useful tool for measuring the circulating levels of specific antibodies. Investigators used this technology to determine the specific antibody responses induced by a granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting whole cell immunotherapy in a clinical trial in patients with prostate cancer.8The production of antibodies against T-cell alternative reading frame protein (TARP), a protein associated with prostate cancer initiation, was correlated with increased survival time. This result demonstrates the potential for protein microarrays as biomarker assays.  Although many trials for new immunotherapies are under way, there is an absence of biomarker assays that are validated, informative, and reliable. Better patient stratification and monitoring using biomarkers would benefit not only clinical applications of immuno-oncology, but also the development of new therapies. The renewed emphasis on biomarker identification is a necessary step to unlocking the full potential of cancer immunotherapies.