Immunotherapy modestly improves response rates in HR+ breast cancer

Patients with HR+/HER2‒ breast cancer treated with immunotherapy show modest improvements in complete response rates, reports a study.

However, immunotherapy is associated with increased toxicity and demonstrates inconsistent improvements in overall (OS) and progression-free survival (PFS).

Researchers conducted a systematic search of PubMed, Embase, Medline, Cochrane Library, and ClinicalTrials.gov through May 2025, following PRISMA guidelines. They identified clinical trials assessing immunotherapy, either alone or in combination, in HR+/HER2‒ breast cancer patients.

Random-effects models were then used to perform meta-analyses, with pooled risk ratios (RRs) and event rates. The research team assessed heterogeneity using I² statistics.

Eleven randomized controlled trials involving a total of 7,480 patients (3,742 immunotherapy and 3,738 control) met the eligibility criteria.

Overall (RR, 1.20, 95 percent confidence interval [CI], 0.92‒1.55) and partial response rates (RR, 1.03, 95 percent CI, 0.54‒1.94) did not significantly improve with immunotherapy vs control.

However, immunotherapy elicited improvements in complete response (RR, 1.63, 95 percent CI, 1.34‒1.97). It also resulted in more therapy-related adverse events (RR, 1.29, 95 percent CI, 1.04‒1.60).

Pooled analysis revealed a median OS of 23.6 months and a median PFS of 6.6 months. The pooled complete response, partial response, stable disease, and progressive disease rates were as follows: 8 percent, 27 percent, 51 percent, and 23 percent.

Patients in the immunotherapy arm had an overall mortality rate of 4 percent.

“Further biomarker-driven trials are warranted,” the researchers said.