Favorable outcome of immunotherapy use in metastatic HR+/HER2- breast cancer: a population-based cohort study

Uncertainty persists regarding the efficacy of immunotherapy for patients with advanced HR+/HER2- breast cancer. We aimed to assess the survival benefit of immunotherapy in metastatic HR+/HER2- breast cancer.

Patients diagnosed with de novo metastatic HR+/HER2- breast cancer from 2013-2021 were analyzed using data from the National Cancer Database. Logistic regression analysis was performed to estimate factors linked to immunotherapy use. Survival outcomes were evaluated through propensity score-matching (PSM), along with Kaplan-Meier methodology and Cox regression models.

A total of 17 211 metastatic HR+/HER2- breast cancer patients were included, of whom 1571 patients receiving immunotherapy were matched 1:1 with 1571 patients not receiving immunotherapy. The immunotherapy use was more common among those with higher burden of lymph node metastasis [odds ratio (OR): 1.35; 95% confidence intervals (CIs): [1.13-1.62]; P= 0.001], and those received hormone therapy (OR: 1.21; 95% CI: [1.04-1.39]; P = 0.012) and radiotherapy (OR: 1.19; 95% CI: [1.06-1.33]; P= 0.002). Survival analysis indicated that patients who had undergone immunotherapy had a significantly improved overall survival (OS) compared with patients who had not both before (hazard ratio [HR]: 0.75; 95% CI: [0.70-0.80]; P < 0.001) and after PSM (HR: 0.77; 95% CI: [0.70-0.85]; P < 0.001). Moreover, survival benefit from usage of immunotherapy was also statistically significant in subgroups received hormone therapy (HR: 0.62; 95% CI: [0.51-0.76]; P < 0.001) or chemotherapy (HR: 0.67; 95% CI: [0.48-0.92]; P = 0.015) only.

Immunotherapy may be beneficial for the OS of patients with de novo metastatic HR+/HER2- breast cancer. Our data may provide clues for the integration of immunotherapy into future clinical treatment strategies.