- Combination immunotherapy is necessary.
- Mechanisms exploited by SCLC to evade immune-mediated rejection need to be identified.
- Inclusion of strategies for driving tumor-reactive T cells into the tumor microenvironment should be considered.
- PD-1 blockade should continue.
- Biomarkers should be identified for selecting patients for tumor microenvironment–targeted agents.
Clinical and molecular biomarkers
Dr. Lauren Averett Byers
Indeed, there is much work to do with respect to biomarkers, but their use in the selection of SCLC patients for immunotherapy is “finally starting to evolve and evolve more rapidly,” according to Lauren Averett Byers, MD, of the University of Texas MD Anderson Cancer Center, Houston.
Numerous groups are identifying biomarkers for both targeted therapy and immunotherapy, Dr. Byers said, noting that “this has been a really incredible time for those of us who take care of small cell lung cancer patients.”
“It’s been many decades since we’ve had a new option for our patients ... and so I think with the landmark clinical trials ... we really do have a new option in terms of a new standard of care,” she said of immunotherapy. “But I think we also recognize that there is significant room for further improvement.”
Many patients don’t respond or don’t respond as well as hoped, and therefore an “incredible need” exists for personalized biomarker-driven therapy for SCLC and its distinct molecular subsets, she said.
Emerging and potential biomarkers and other factors to guide treatment decisions include TMB, PD-L1, clinical history/duration of response in immunotherapy-naive relapsed patients, gene expression profile–driven SCLC subgroup identification, and DNA damage response (DDR) inhibitors such as Chk1, PARP, and Wee1 inhibitors.
TMB, as described by Dr. Antonia with respect to the CheckMate 032 findings of improved outcomes in those in the highest TMB tertile, is one potentially helpful biomarker for response.
“In thinking about how we apply this, though, we have to think about what we’re deciding between,” Dr. Byers said, explaining that the responses in patients with medium or low TMB – between 0% and 10% in most studies in the relapsed SCLC setting – aren’t that different from those seen with other treatment options.
“Currently we’re not routinely ordering TMB to decide on immunotherapy because there are still patients that can be as likely to benefit from immunotherapy as they are from chemotherapy, and potentially with more durable responses,” she said. “But certainly, it is a way to potentially identify patients where immunotherapy alone may have very high rates of response.”
IMPower133 showed no difference in hazard ratios for death based on TMB detected in the blood in SCLC patients treated with first-line atezolizumab plus chemotherapy, but “this still supports using the immunotherapy/chemotherapy combination broadly, and also emphasizes the need for an improved – and probably expanded – look at other biomarkers that may help predict response,” she said.
PD-L1 appears to have a role as a biomarker in this setting as well, she said, citing the KEYNOTE-028 findings of numerically improved responses in PD-L1–positive SCLC patients treated with pembrolizumab.
“We should be looking at PD-L1 levels, but we need further information to know how we might use this,” she said.
In immunotherapy-naive patients who relapse after front-line chemotherapy, the most important biomarker is clinical history and duration of response to platinum, which helps guide second-line treatment, Dr. Byers said.
“I think there’s consensus among most of us that patients who have platinum-refractory disease and are unlikely to respond to further platinum therapy or other chemotherapy agents are patients who really should get immunotherapy,” she added, explaining that the available data suggest there is no cross-resistance and that there may actually be enhanced benefit with immunotherapy in such patients.
Using molecular data to identify SCLC subtypes based on gene expression profiles is another area of interest, she said.
In fact, new data presented at the WCLC conference by Carl Gay, MD, PhD, a former fellow in her lab and now a junior faculty member at MD Anderson, identified four specific SCLC subgroups; three were driven by activation of the known transcription factors ASCL1, NEUROD1, and POU2F3, but an additional “inflamed” group without expression of those three transcription factors was also identified.
That “triple-negative” group had significantly higher expression of human leukocyte antigen and very high T-cell activation with expression of multiple immune checkpoints representing candidate targets, she said, adding: “We hypothesize that this group may be the group in SCLC that gets relatively greater benefit from immune checkpoint blockade.”
DDR is also garnering attention.
“Since there was this signal that [patients with] DNA damage ... tend to be more sensitive to immunotherapy ... we looked at whether or not targeted agents that prevented repair of DNA damage and induced increased levels of DNA damage ... might activate the innate immune system through the STING pathway and if that could be a potential approach to enhance immunotherapy response,” she said.
The approach showed promise in cell lines in a mouse model and also in an immunocompetent SCLC mouse model.
“It was really interesting to see how these drugs might potentially enhance response to immunotherapy,” Dr. Byers said, noting that the same phenomenon has been seen with PARP inhibitors in breast and colon cancer models and in other solid tumors.
“So I think that there is something there, and fortunately we’re now at a point now where we can start looking at some of these combinations in the clinic across many different cancer types,” she said. “I think we’ll be learning a lot more about what’s happening with these patients.”
At present, however, “there is more that we don’t know about the immune landscape of small cell lung cancer than what we do know, and that’s a real opportunity where, over the next several years, we will gain a deeper understanding ... that will direct where we’re going in terms of translating that back into the clinic.”