Association of improved survival (OS) and tumor control (TC) with interleukin-2 (IL2) with development of immune-related events (IREs): Data from the PROCLAIMSM registry.

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9528 Background: IREs are associated with immunotherapy (IT) for cancer and while reports suggest improvement in TC and OS with induced IREs, the long-term impact is unclear. IL2 has been the major IT for patients (pts) with renal cell carcinoma (RCC) and melanoma (MM) since 1992. We evaluated IREs reports in the PROCLAIMSM data base (2008-2016) of IL2-treated pts. Methods: Reports on 614 (MM) and 843 (RCC) pts were queried for IREs. IREs were categorized as occurring before, during, or after IL-2 and related to any checkpoint inhibitor (CPI). TC (CR+PR+SD) was compared between no IRE and IRE, using Fisher’s exact test. OS curves were estimated by Kaplan-Meier method, and comparison of no IRE/before IL2 with during/after IL2, was analyzed by log-rank test. Results: With a median (med) follow-up of 3.5+ years (range 1-8+ year), 140 IREs were reported in 118 pts (9.6% of all PROCLAIMSM pts): 93 (15%) in MM; 47 (5.6%) in RCC. 25 IREs were prior to IL2; 13 IREs were during IL2; 102 were after IL2. Of the latter 102, 31 were after IL2 and after subsequent CPI; 71 were attributed to IL2 only; and in 13, IREs were due to either IL2 or CPI. TC was 73% for IRE group vs 56% for no IRE group (p = 0.0054). OS was significantly greater for IRE group during/after IL2 compared to no IRE/before IL2 in MM, med 46 months (mo) vs 18 mo (p = 0.0001) and in RCC, med 61 mo vs 43 mo (p = 0.0196), independent of CPI IREs. Med # of IL2 doses was 19 in no IRE group, 39 in IRE during IL2 group, and 25 in IRE after IL2 group. IL2-related IREs were primarily vitiligo and thyroid dysfunction (70% of IL2 IREs), with limited further impact, while CPI-related IREs were often serious, requiring intervention (hypophysitis, colitis, hepatitis, uveitis) (52% of CPI IREs) and possibly chronic management. Conclusions: IREs following IL2 are associated with improved TC and OS. IREs resulting from IL2 and from CPIs are qualitatively different and likely reflect different mechanisms of action of immune activation and response.