Abstract B069: Seasons of risk: Investigating temporal trends in ICI-associated Myocarditis

Abstract Introduction Myocarditis is a known complication of immune checkpoint inhibitor (ICI) therapy. Viral myocarditis often follows seasonal patterns, raising the question of whether ICI-associated myocarditis may also exhibit temporal variation or periods of heightened susceptibility. Identifying temporal clustering may guide targeted monitoring strategies during higher-risk periods. Given the modest sample size, the analyses were designed as exploratory and hypothesis-generating. Methods We identified 54 high-suspicion cases of ICI-associated myocarditis through inpatient consults, outpatient follow-up, or troponin monitoring. Six patients were excluded: two without confirmed ICI exposure, two without documented troponin elevation, one with inaccessible records, and one with a missing ICI start date, yielding a final cohort of 48 patients. Cases were grouped by peak year as pre-COVID (before 2020), during COVID (2020-2021), or post-COVID (2022-2025). Seasonality was assessed by comparing January-June versus July-December, a half-year grouping chosen to ensure adequate statistical stability with limited sample size. Statistical analyses included Fisher’s exact Test and binomial testing. Results Among 48 high-suspicion ICI-myocarditis cases, ICIs were most commonly initiated for gastrointestinal (17%), lung (15%), head and neck (13%), and melanoma (13%) cancers. Pembrolizumab was the predominant regimen (54%), followed by ipilimumab + nivolumab (25%), cemiplimab (8%), nivolumab (6%), durvalumab (4%), and envafolimab (2%). Most patients (77%, 37/48) experienced symptom onset within the first two months of ICI initiation. A greater proportion of ICI-myocarditis events occurred between July and December (31/48, 64.6%) compared with January-June (17/48, 35.4%), although this did not reach statistical significance (binomial test, p = 0.059). This seasonal pattern persisted across troponin thresholds: 70% (16/23) of cases >100 ng/L, 70% (23/33) >500 ng/L, and 63% (25/40) >1000 ng/L occurred between July and December. Although elevated troponin cases were numerically higher post-COVID, the difference was not statistically significant (Fisher’s exact p = 0.496). Conclusions Most ICI-myocarditis cases occurred within two months of treatment initiation, with a skew toward the latter half of the year suggesting a potential seasonal pattern in early-onset cardiotoxicity. This trend may reflect interactions between increased ICI use, improved surveillance, or immunologic priming related to COVID-19 infection or vaccination. While preliminary, these findings support further investigation into temporal and immunologic risk factors that may inform risk-adapted monitoring strategies. Citation Format: Crystal Griffith, Elizabeth Park, Evaline Cheng, Stephen McCroskey, Tamiko Katsumoto, Han Zhu, Pauline Funchain. Seasons of risk: Investigating temporal trends in ICI-associated Myocarditis [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B069.