Immunotherapy improves complete response but lacks overall response benefit in HR+ breast cancer

This systematic review and meta-analysis examined the efficacy and safety of immunotherapy in patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative breast cancer. The analysis included a total sample size of 7480 patients. The setting of the included studies was not reported in the source data. The intervention involved immunotherapy administered alone or in combination with other treatments. The comparator was a control group receiving standard care or placebo. The follow-up period for the pooled data was 6.6 months.

The primary outcome measured was overall response rate. The pooled relative risk was 1.20 with a 95% confidence interval of 0.92-1.55. The p-value was not reported. The direction of the effect indicated no significant improvement compared with control. This finding suggests that immunotherapy does not consistently enhance the overall response rate in this specific patient population.

Secondary outcomes included partial response rate, complete response, overall survival, progression-free survival, and overall mortality. The pooled relative risk for partial response rate was 1.03 with a 95% confidence interval of 0.54-1.94. The direction indicated no significant improvement. For complete response, the pooled relative risk was 1.63 with a 95% confidence interval of 1.34-1.97. This direction indicated improved complete response rates. The pooled rate for complete response was 9%. The pooled rate for partial response was 27%. The pooled rate for stable disease was 51%. The pooled rate for progressive disease was 23%.

Safety and tolerability findings showed that immunotherapy was associated with higher therapy-related adverse events. The pooled relative risk for therapy-related adverse events was 1.29 with a 95% confidence interval of 1.04-1.60. Serious adverse events, discontinuations, and specific tolerability metrics were not reported. Overall mortality in the immunotherapy group was 4%.

The pooled median overall survival was 23.6 months. The pooled median progression-free survival was 6.6 months. Specific p-values or confidence intervals for these survival metrics were not reported. These results must be interpreted with caution as the source data did not provide detailed statistical significance for survival endpoints.

Key methodological limitations include the lack of reported setting details and the absence of specific p-values for survival outcomes. The study type is a meta-analysis, which aggregates data from multiple primary studies. The certainty of the evidence is limited by the heterogeneity often found in such pooled analyses. The do not overstate section notes that immunotherapy lacks consistent improvements in overall or progression-free survival. It may modestly enhance complete response rates but is associated with increased toxicity.

Clinical implications suggest that clinicians should weigh the potential for improved complete response against the risk of higher therapy-related adverse events. The lack of significant improvement in overall response rate or survival metrics questions the routine use of immunotherapy in this setting. Questions remain unanswered regarding which specific subgroups might benefit most. The funding or conflicts of interest were not reported. The practice relevance was not explicitly stated in the source data. Causality notes were not reported. The overall mortality rate of 4% provides a baseline for risk assessment.