Background: Given underlying differences in the tumor microenvironment across metastatic sites, ICIs demonstrate variable efficacy depending on sites of met involvement. Data on the safety and outcomes of pts on ICIs with cardiac mets are limited. Methods: In an international multi-center retrospective study, pts with solid tumors and baseline mets to the heart who had received ≥1 cycle of ICIs were included. Immune-related adverse events (irAEs) were graded per CTCAE v5.0. Objective response rates (ORR) were evaluated by RECIST1.1 when available. Median overall survival (mOS) and median progression-free survival (mPFS) were calculated from time of ICI initiation using the Kaplan-Meier method. Results: 110 pts across 20 institutions were identified with a median follow-up of 36 (95% CI 26-51) months. Melanoma (38%, n=42) and non-small cell lung cancer (NSCLC, 24%, n=26) were the most common cancers. Median age at ICI initiation was 65 (IQR: 59-75) years and 29% (n=26) received combination ICI therapy with anti-PD1 and anti-CTLA4. Overall, 62% (n=68) received ICIs as 1^st line. The mets were mostly located in the atria (37%, n=41) and ventricles (35%, n=39). At ICI initiation, 21% (n=23) had a cardiac thrombus. Of 78 pts with available echocardiographic data at time of ICI initiation, the mean ejection fraction was 61+/- 7.1%. Cardiology referrals and cardiac MRIs since time of cancer diagnosis were completed on 53% (n=58) and 47% (n=52) of pts, respectively. Overall, 36.4% (n=40) of pts had cardiac complications from the mets, including arrhythmias (13%, n=14), arterial/venous emboli (3.6%, n=4), and cardiac tamponade (2.7%, n=3). For NSCLC, ORR, mPFS (95% CI), and mOS (95% CI) were 23%, 4.4 months (3.0-7.5), and 9.9 months (5.9-14.7), respectively. For melanoma, ORR, mPFS, and mOS were 35.7%, 9.1 months (5.2-20), and 29 months (14-58), respectively. Cardiac met ORRs for NSCLC and melanoma were 27% and 43%, respectively. 74% (N=71/96) of pts with evaluable response data had concordant response in the burden of overall disease and cardiac disease. IrAEs are shown. Conclusions: Although cardiac mets are frequently associated with cardiac complications, ICIs demonstrate meaningful efficacy with no overtly concerning safety signals. Close to three-quarter of pts have concordant response in the overall disease and cardiac disease burden. Multi-disciplinary approach involving cardiologists and oncologists need to be implemented to appropriately manage pts with cardiac mets.

*Sum of individual irAEs does not add up to total as a subset of pts had more than one irAE.