Hormone receptor positive (HR+) breast cancer is typically treated by blocking or removing estrogen, which hormone receptor positive breast tumors rely on. Drugs like tamoxifen, aromatase inhibitors, and newer agents like selective estrogen receptor degraders (SERDs) are effective, but over time tumors may become resistant, especially in advanced stages.

Immunotherapy, which is a treatment that boosts the body’s immune response, has revolutionized care for cancers such as melanoma and lung cancer. These often use “checkpoint inhibitors,” which release the brake on immune cells. While these work well in aggressive breast cancers like triple-negative subtypes, HR+ tumors generally have low mutation rates, few immune cells, and little PD-L1 protein, making them less responsive.

The study, The Role of Immunotherapy and Immune Modulators in Hormone-Positive Breast Cancer: Implications for Localized and Metastatic Disease, found that while immune checkpoint inhibitors like pembrolizumab and atezolizumab have shown promising results in combination with chemotherapy for triple negative breast cancer, their efficacy in HR+ breast cancer has generally been modest. However, other recent studies indicate that such therapies may help overcome endocrine resistance in metastatic disease. Furthermore, immune modulators, including cytokines and myeloid-derived suppressor cell inhibitors, are being investigated for their ability to reshape the tumor microenvironment, potentially enhancing the immune response and improving treatment outcomes. Despite these advances, challenges remain in identifying predictive biomarkers and managing immune-related adverse events.
While it’s not yet standard care, the future of HR+ breast cancer treatment may include immunotherapy as part of combination therapy. Ongoing research into which patients benefit most will be key to harnessing its full potential.

Reference: O’Farrell J, Lapp C, Kuznia H, Afzal MZ. The Role of Immunotherapy and Immune Modulators in Hormone-Positive Breast Cancer: Implications for Localized and Metastatic Disease. J Clin Med. 2025;14(12):4322. Published 2025 Jun 17. doi:10.3390/jcm14124322.