The landscape of immunotherapy biomarkers is rapidly evolving, and future developments are likely to have an impact on patients and clinicians alike.
The landscape of immunotherapy biomarkers is rapidly evolving, and future developments are likely to have an impact on patients and clinicians alike, said Kurt A. Schalper, MD, PhD, in a virtual presentation during the 5th Annual International Congress on Oncology and Pathology™.1
“The 2 major immune checkpoint blockers that are widely used are CTLA-4 and PD-1/PD-L1,” said Schalper, an assistant professor of pathology and medical oncology at the Yale School of Medicine and the Director of the Translational Immuno-oncology Laboratory at the Yale Cancer Center in New Haven, Connecticut. “CTLA-4 works more on the T-cell priming stage and by blocking an inhibitor receptor that stimulates lymphocytes. PD-1/PD-L1 is believed to act more on the tumor microenvironment, blocking the PD-1 inhibitor receptor, and restimulating T cells.”
According to Schalper, the spectrum of biomarkers can be as complex as the clinical development of the checkpoint inhibitors themselves. Immune markers include PD-L1 expression, tumor infiltrating lymphocytes, and the microbiome of the gut. In terms of tumor markers, which are primarily genomic, examples include mismatch repair deficiency and tumor mutational burden (TMB).
To date, the FDA has approved agents based on PD-L1 immunohistochemistry, microsatellite instability (MSI) status, and TMB for a variety of tumor types, many of which are very different biologically. This complexity is clearly paired with the need for biomarkers that physicians can use when making treatment decisions, Schalper said.
“One interesting thing is that nothing is always black-and-white,” said Schalper. “There are metrics that have not received regulatory approval that some people are starting to use; this is kind of a gray area. Tumor infiltrating lymphocytes is a standard, traditional method of immunohistochemistry that some are starting to use [as a biomarker.]
“This is a rapidly-evolving field, and we expect a lot of changes.”
PD-L1, although it can at times be fraught due to non-interchangeable expression-scoring formulas, among other factors, generally works well as a biomarker, explained Schalper. In the Keynote-024 study (NCT02142738), investigators assessed pembrolizumab (Keytruda) as a frontline therapy for patients with non-small cell lung cancer (NSCLC). Patients with a PD-L1-positivity rate of greater than 50% according to tumor proportion score (TPS) had superior progression-free survival (PFS) when treated with pembrolizumab compared with chemotherapy (HR, 0.50; 95% CI, 0.37-0.68; P < .001).2
Alternatively, in the Checkmate 026 study (NCT02041533), which used a much lower TPS threshold of 5%, patients with NSCLC did not experience a PFS benefit with nivolumab (Opdivo) as a frontline therapy compared with chemotherapy (HR, 1.15; 95% CI, 0.91-1.45; P = .25).3
In the IMpower110 study (NCT02409342), patients with NSCLC and a PD-L1 expression of TC3 or IC3 treated with atezolizumab (Tecentriq) monotherapy had superior overall survival (OS) compared with patients treated with chemotherapy (HR, 0.59; 95% CI, 0.40-0.89; P = .01) vs chemotherapy.4 In CheckMate 227 (NCT02477826), patients with NSCLC and a PD-L1 expression rate of at least 1% derived an OS benefit from the combination of nivolumab and ipilimumab (Yervoy) compared with chemotherapy (HR, 0.79; 95% CI, 0.67-0.93).5
“This was not only in lung cancer, but it was also seen over and over [in other cancer types],” said Schalper. “This [biomarker] works, but it does not always work the same and the assay doesn’t predict the same way. The cut-points seem to be different across treatments and across diseases.”
In June 2020, the FDA granted accelerated approval for pembrolizumab as a treatment for adult and pediatric patients with unresectable or metastatic TMB-high solid tumors whose disease has progressed on other treatments. According to Schalper, TMB is a continuous variable—tumors could have very few or thousands of mutations. Furthermore, as with PD-L1 expression, different studies and assays have arrived at different cut-points for TMB as an immunotherapy biomarker.
“Different labs seem to be getting different scores,” he said. “We are trying to define what is the right amount of sequencing to get reliable scores.”
In terms of MSI status as an immunotherapy biomarker, Schalper said that it has been shown to predict high likelihood of response to immune checkpoint inhibitors. Tumors with high MSI expression have increased sensitivity to immunotherapy, and Schalper explained that MSI status is a biomarker in several tumor types including include gastric, uterine, and colon carcinomas.
Future directions for immunotherapy biomarkers include refining available markers, integrating biomarkers, and the development of novel biomarkers. mRNA and inflammation signatures are seen as potential areas of refinement of the current biomarkers. Combining biomarkers that are not redundant, such as TMB and PD-L1 expression, is also seen as an area of future growth.
“There are a number of next generation sequencing essays being developed...that will likely impact the clinical space very soon,” Schalper said. “There are a number of future developments—we're probably going to hear a lot from circulating biomarkers, ctDNA, [and] deep tissue analysis with high multiplexing spatially-resolved analysis.”