Outcomes of immunotherapy in hormone receptor–positive breast cancer: A systematic review and meta-analysis.

Abstract

e13094 Background: Immunotherapy offers a promising approach for triple negative breast cancer; however, its effectiveness and safety remain uncertain in hormone receptor-positive (HR+) breast cancer. Here, we perform a systematic review and meta-analysis to evaluate efficacy and safety in HR+ breast cancer patients who received immunotherapy (intervention) versus patients who received traditional treatment (control). Methods: A systematic search was conducted on PubMed, Cochrane, and Clinicaltrials.gov following PRISMA guidelines and eleven studies reporting outcomes of immunotherapy in HR+ breast cancer were included after screening of 313 studies. Inter-study variance was assessed using the Der Simonian-Laird Estimator, and pooled analysis was conducted with 95% confidence intervals using the ‘meta’ package in R (version 4.16-2). Results: A total of 2308 patients (intervention:1256, control 1052) from 11 clinical trials (2020-2024) were included in the analysis. The median age was 54.1 (24-87) years and majority were female (99.6%, n = 996/1000). All patients had HR+/HER2-negative breast cancer with 97.5% (n = 2250) having stage IV. The median follow-up was 19.7 months (0.4-51.8). Immunotherapies administered in intervention arm included pembrolizumab (63%, n = 793), nivolumab (22%, n = 278), eftilagimod alpha (9%, n = 114), and atezolizumab (6%, n = 71). The median number of prior therapies was 2 (range 0-5). When compared between intervention and control groups, the risk ratios for overall response (OR), complete response (CR), and partial response (PR) were 1.20 (95% CI: 0.92 - 1.55, I 2 = 0, p = 0.4, n = 409), 1.63 (95% CI 1.34-1.97, I 2 = 0%, p = 0.6, n = 1788), and 1.03 (95% CI 0.54-1.94, I 2 = 11%, p = 0.32, n = 196), respectively. The risk ratios for stable disease (SD) and progressive disease (PD) were 1.37 (95% CI 0.95-1.99, I 2 = 0%, p = 0.69, n = 196) and 0.52 (95% CI 0.15-1.8, I 2 = 81%, n = 108, p = 0.3, n = 196). The risk ratios for therapy-related adverse events (TRAE) and overall mortality (OM) were 1.29% (95% CI 1.04-1.6, I 2 = 69%, p = 0.01, n = 2218) and 1.87 (95% CI 0.89-3.9, I 2 = 0%, p = 0.79, n = 831), respectively. Conclusions: Immunotherapy resulted in higher response rates but increased adverse events and mortality rates were encountered. Large cohort studies are needed to further explore the potential of immunotherapy in HR+ breast cancer.