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

Abstract

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.