More details of the POSEIDON trial
In the POSEIDON trial, investigators had the choice of different chemotherapy regimens: platinum/gemcitabine for patients with squamous disease, platinum/pemetrexed for patients with nonsquamous disease, and nab-paclitaxel/carboplatin for patients with disease of either histology, Dr. Johnson reported.
It is noteworthy that the majority of patients were from Eastern Europe and Asia, “and the proportion of squamous patients enrolled was higher than is typically seen in mixed histology lung cancer studies,” she added.
The patients were stratified by PD-L1 expression at a cutoff of 50%, disease stage, and tumor histology.
Overall, 1,013 patients were enrolled. The three treatment arms were relatively well balanced in terms of baseline characteristics.
Dr. Johnson noted that there were “a few minor imbalances” in the durvalumab plus tremelimumab arm, with “fewer females, fewer Asians, and fewer never-smokers relative to the other two arms.”
The primary endpoint analysis after a median follow-up of 10.3 months demonstrated that PFS was significantly improved with durvalumab plus chemotherapy over chemotherapy alone, at a median of 5.5 months versus 4.8 months (hazard ratio, 0.74; P = .00093).
Although OS improved numerically with the addition of durvalumab to chemotherapy, it did not reach significance (13.3 months vs. 11.7 months with chemotherapy alone; HR, 0.86; P = .07581).
The positive PFS benefit with durvalumab plus chemotherapy triggered a secondary endpoint analysis, which showed that adding tremelimumab to durvalumab plus chemotherapy improved both survival outcomes.
Median PFS with the triple combination therapy was 6.2 months, significantly longer than the 4.8 months seen with chemotherapy alone (HR, 0.72; P = .00031).
At 12 months, 26.6% of patients who underwent treatment with durvalumab plus tremelimumab plus chemotherapy had not experienced disease progression, compared with 13.1% in the chemotherapy-alone arm.
OS was also significantly improved, at 14.0 months among patients in the triple therapy arm versus 11.7 in the chemotherapy-alone arm (HR, 0.77; P = .00304).
The results also showed that at 24 months, 32.9% of triple therapy patients were still alive versus 22.1% in the chemotherapy-alone arm.
Analysis indicated that “most subgroups favored the addition of immunotherapy to chemotherapy.” There was a “trend toward improved survival for all patients treated with durvalumab plus tremelimumab plus chemotherapy,” Dr. Johnson said.
This was seen “in particular for the nonsquamous patients” and for those with tumor PD-L1 expression of less than 1%, he added.
It is notable that for a large proportion of combination-therapy patients, response had continued at 12 months. This was the case for 38.9% of those who underwent treatment with durvalumab plus chemotherapy and for 49.7% of those given triple therapy versus 21.4% in the chemotherapy-alone arm.
As was seen across the whole cohort, among patients with nonsquamous disease, PFS and OS improved with the addition of immunotherapy. Of those patients with nonsquamous disease, 95.5% received pemetrexed plus platinum chemotherapy.
However, among patients with squamous tumors, of whom 88.3% received gemcitabine plus platinum chemotherapy, PFS and OS were “poor ... across all treatment arms,” Dr. Johnson reported, “with little separation of the curves.”
She highlighted the fact that the proportion of patients who experienced grade 3/4 adverse events, whether of any cause or treatment related, was only slightly higher in the two immunotherapy arms, indicating that “most events were driven by the chemotherapy.”
The rates of treatment discontinuation and adverse events leading to death were also similar across the three treatment arms, albeit they were slightly higher with the addition of immunotherapy.
Dr. Johnson also noted that, although there were more immune-mediated adverse events with durvalumab plus tremelimumab plus chemotherapy, compared with durvalumab plus chemotherapy, the “majority were grade 1/2 and were manageable.”
The most common immune-mediated events in the two immunotherapy arms were hypothyroid and hepatic events, pneumonitis, dermatitis, and rash.
The study was sponsored by AstraZeneca. Dr. Johnson reported numerous relationships with pharmaceutical companies. Dr. Brahmer reported relationships with Amgen, AstratZeneca, BMA, Genentech/Roche, Eli Lilly, Eisai, GlaxoSmithKline, Janssen, Merck, RAPT Therapeutics, Regeneron, Revolution Medicine, and Sanofi.
A version of this article first appeared on Medscape.com.