Abstract PS14-01: Immune related adverse events in patients ≥65 years vs. 65 years with breast cancer treated with immunotherapy

Abstract Background: Pembrolizumab is approved for early/advanced triple negative breast cancer (TNBC), and atezolizumab was previously approved for advanced TNBC. Toxicity of immunotherapy (IO) and immune related adverse events (irAEs) in patients ≥65 years with TNBC is not described in detail in results from registration trials (KEYNOTE 522, KEYNOTE 355, and IMPassion130), where patients ≥65 years were a minority. Understanding real-world IO toxicity and irAEs in patients with breast cancer ≥65 years may inform clinical decision making. Methods: We studied IO toxicity and irAEs in patients with breast cancer ≥65 years vs. 65 years (at IO start) who received IO at an academic institution. A retrospective review was conducted to identify IO toxicity and irAEs (classified by CTCAE v 5.0). Cohorts were compared with Pearson's chi-squared test (categorical variables) and Wilcoxon rank-sum test (continuous variables). Results: Cohorts had 25 patients ≥65 years (median age 73 years, interquartile range (IQR) 69-74 years) and 104 patients 65 years (median age 48 years, IQR 39-56 years). Stage I-III/IV breast cancer distribution was 36%/64% for ≥65 years and 68%/32% for 65 years. Baseline ECOG performance status was mainly 0-1 in both cohorts. IO was mainly pembrolizumab (≥65 years: 96%; 65 years: 83% for first IO regimen) vs. atezolizumab. Table 1 depicts characteristics of IO toxicity. IO duration was longer in patients 65 years. While rates of IO interruption for toxicity and discontinuation for toxicity were numerically higher in patients ≥65 years, these findings did not reach statisticial significance, possibly due to the sample size. Similar overall rates of irAEs were seen (≥65 years: 72%; 65 years: 65%, p=0.47) but there were differences in the types of irAEs. Patients 65 years had more transaminitis (≥65 years: 12%; 65 years: 33%, p=0.04), and grade 2-3 hypothyroidism (among patients developing hypothyroidism, ≥65 years: grade 1- 75%, grade 2- 25%, grade 3- 0%; 65 years: grade 1- 11%, grade 2- 79%, grade 3- 11%, p=0.017). Conversely, patients ≥65 years had higher rates of irAE nephritis (≥65 years: 12%; 65 years: 1%, p=0.004); notably, none of the patients had baseline chronic kidney disease. Rates of full resolution of irAEs were similar between cohorts (≥65 years: 67%; 65 years: 57%, p=0.47), but patients ≥65 years had more steroid use for management of first irAE while patients 65 years required more thyroid hormone supplementation (first irAE management distribution, ≥65 years: steroids- 71%, thyroid hormone- 7%, supportive care- 21%; 65 years: steroids- 31%, thyroid hormone- 25%, supportive care- 44%, p=0.025). Late onset irAEs and deaths from irAEs were rare in both cohorts, with 1 irAE related death in the cohort ≥65 years. Conclusions: In this real-world cohort, similar overall rates of irAEs were observed in patients ≥65 years and 65 years. However, patients ≥65 years had higher rates of irAE nephritis and steroid use for irAEs, while patients 65 years had more transaminitis and higher grade hypothyroidism, requiring more thyroid hormone supplementation. Given these age specific differences, validation in a larger cohort is merited. Table 1. Characteristics of IO toxicity. Citation Format: Neelima Vidula, Jennifer Hutchinson, Abigail McLaren, Lianne Ryan, Andrzej Niemierko, Aditya Bardia. Immune related adverse events in patients ≥65 years vs. 65 years with breast cancer treated with immunotherapy abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS14-01.