The majority of deaths from breast cancer occur following the development of metastatic disease, a process inhibited by β-blockers in preclinical studies. This phase II randomized controlled trial evaluated the effect of preoperative β-blockade with propranolol on biomarkers of metastatic potential and the immune cell profile within the primary tumor of patients with breast cancer.

In this triple-blind placebo-controlled clinical trial, 60 patients were randomly assigned to receive an escalating dose of oral propranolol (n = 30; 80–160 mg daily) or placebo (n = 30) for 7 days prior to surgery. The primary endpoint investigated the effect of propranolol on prometastatic and proinflammatory gene expression within the primary tumor.

Propranolol downregulated primary tumor expression of mesenchymal genes (P = 0.002) without affecting epithelial gene expression (P = 0.21). Bioinformatic analyses implicated downregulation of Snail/Slug (P = 0.03), NF-κB/Rel (P < 0.01), and AP-1 (P < 0.01) transcription factors in structuring the observed transcriptome alterations, and identified changes in intratumoral neutrophil, natural killer cell, and dendritic cell recruitment (all P < 0.01). Patients with clinical evidence of drug response (lowered heart rate and blood pressure) demonstrated elevated tumor infiltration of CD68⁺ macrophages and CD8⁺ T cells.

One week of β-blockade with propranolol reduced intratumoral mesenchymal polarization and promoted immune cell infiltration in early-stage surgically-resectable breast cancer. These results show that β-blockade reduces biomarkers associated with metastatic potential, and support the need for larger phase III clinical trials powered to detect the impact of β-blockade on cancer recurrence and survival.

See related commentary by Blaes et al., p. 1781