Why carboplatin, pemetrexed and pembrolizumab have become my new go-to regimen for first-line non-squamous NSCLC treatment.

By Jonathan W. Goldman, MD

Metastatic non-small cell lung cancer (NSCLC) treatment has generally improved by optimizing care for “slices of the pie”—pieces of a pie chart representing all of lung cancer patients. Initially, mutation-based treatment led the way; 10% of lung cancers were identified as EGFR-mutant and treated with appropriate tyrosine kinase inhibitors. Subsequently, thinner and thinner slices of the population, each 1-7% of NSCLC patients, have been described and their cancers targeted. More recently, immunotherapy entered the picture, but again the greatest benefit of this therapy was limited to the 20-25% of patients that were PD-L1 positive. Despite all of these advances, we still had at least half of patients receiving more than 10-year-old chemotherapy as their initial treatment.

We now have preliminary evidence that this may be changing. Langer, et al reported in November 2016 (Lancet Oncology) the phase 2 KEYNOTE-021-G1 cohort of non-squamous NSCLC patients treated with the standard, carboplatin and Alimta (pemetrexed), alone or with the PD-1 inhibitor, Keytruda (pembrolizumab). Previous attempts to add to a platinum-doublet had generally provided marginal benefits at best (for example, with Avastin [bevacizumab] or Erbitux [cetuximab]). In contrast, the 021G trial suggested massive benefits, at least as far as response rate (RR) and progression free survival (PFS).

The 021G trial was a moderate-sized phase 2 trial with 123 patients split between the two arms. With Keytruda added to chemotherapy, the response rate increased from 29 to 55%, and importantly this benefit was irrespective of PD-L1 status (above or below a 1% PD-L1 cutoff). PFS was also significantly improved from 8.9 to 13.0 months with a hazard ratio of 0.53, which represents a decrease in the risk of cancer progression by almost half. Many of the trials leading to new drug approvals especially in an unselected cohort report hazard ratios of 0.75 or 0.80, so the benefit in 021G is staggering. The overall survival curves were overlapping at the time of the initial report, and if they suggested a possible survival benefit when updated at the 2017 ASCO Annual Meeting, there was still no statistically significant difference. This lack of a clear survival benefit is certainly at least in part due to crossover at the time of progression from the chemotherapy alone arm to get Keytruda or another immunotherapy (32% within the study and 74% if you count receiving an immunotherapy agent at any point, on or off the trial).

Furthermore, the toxicity associated with the addition of Keytruda was generally manageable, although moderate to severe toxicity (grade 3 or higher) was increased from 28 to 41%. Primarily, these were hematologic toxicities, including anemia and low blood counts, which oncologists are very comfortable managing. Stereotypical immunotherapy toxicities (such as pneumonitis, colitis or hepatitis) were reported at rates similar to previous experience with single-agent PD1 or PDL1 inhibitor therapy. Nevertheless, Keytruda was discontinued due to toxicities in 10% of patients, including in 1 patient with grade 3 pneumonitis, and doctors and patients will need to be on the lookout for such complications.

Many investigators and thought leaders were surprised when the FDA granted priority review for the front-line Keytruda-chemotherapy combination in January 2017. While lung cancer drug approvals had come from phase 2 or even phase 1 data before, that had consistently been for targeted therapy in areas of unmet need. However, just a few months later, on May 10, 2017 the FDA provided accelerated approval based on the RR and PFS benefits reported from KEYNOTE-021-G1. This does require verification in confirmatory trials including the KEYNOTE-189 trial, which mirrors the 021G trial but in a larger, phase 3 format.

This approval further shocked the lung cancer community. It certainly put standard treatment pathways and clinical trials, both open and in planning, in to disarray. However, from the FDA standpoint, how could you say no to a doubling in the response rate and a 50% decrease in the risk of progression? From the patient standpoint, there is now a novel treatment option that applies to the majority of patients. This is an event to celebrate.

There have been several lines of criticism of this combined treatment modality. The clearest is that if the overall survival curves remain overlapping, it may be advantageous to use chemotherapy and immunotherapy sequentially instead of concurrently. However, it seems likely that if the impressive RR and PFS advantages of concurrent therapy are real, they will translate into a survival advantage. It is also important to remember that patients can worsen rapidly during front-line therapy and never have the opportunity to benefit from a second-line treatment. If a survival advantage is not seen in the small phase 2 trial, it seems likely to be demonstrated in the larger phase 3 trial.

Another criticism of the concurrent approach is the associated medical and financial toxicity. Some presume that most patients will be benefiting from either the chemotherapy or the immunotherapy, and that by giving everything together, we are exposing patients to needless drug toxicity and society to unsustainable costs. One could respond, firstly, we do not know exactly how chemotherapy and immunotherapy may be interacting and there may be synergism beyond the efficacy of the individual parts. (Some hypothesize that tumor cell death via chemotherapy releases antigens that prime an immune response, which is then amplified into an immune effector response by immunotherapy.) Secondly, the toxicity profile as seen in the 021G trial shows that concurrent administration of chemotherapy and PD-1 blockade is tolerable for most patients. Thirdly, we have used expensive triplet regimens before (the best example being carboplatin, Alimta and Avastin) but at least with the 021G triplet there is evidence for major benefit.

In the end, we are all awaiting the confirmatory phase 3 trials of chemoimmunotherapy across many of the PD1 and PDL1 inhibitor drug-development pipelines. In the meantime, I applaud the FDA’s provisional approval and I am happy to be able to provide this as an option for my patients. I have heard some doctors state that they will reserve the triplet for patients that “need a response.” I have never met a patient who did not feel that he or she needed a response, and therefore the 021G triplet is my new go-to first-line regimen for non-squamous NSCLC patients without targetable mutations.

Dr. Goldman joins GRACE from UCLA Medical Center in Santa Monica, where he specializes in Hematology and Oncology.  He serves as Assistant Professor of UCLA Hematology & Oncology, Associate Director of Drug Development and Director of Clinical Trials in Thoracic Oncology.