Multicenter phase 1-2 trial of topical imiquimod and local radiotherapy in patients with breast cancer cutaneous metastases

Imiquimod (IMQ) is a toll-like receptor (TLR)7 agonist. When used locally, it creates an inflammatory environment that promotes tumor antigen cross-presentation and infiltration by effector cells. A multicenter phase 1-2 trial in the United States evaluated the combination of topical IMQ with local radiotherapy (RT) in patients with breast cancer cutaneous metastases. Among 24 patients receiving IMQ/RT with or without cyclophosphamide, systemic responses weren seen in 4 patients and local responses in 19 patients. The treatment was well tolerated, with no grade 4 or 5 treatment-related adverse events, and with manageable grade 3 TRAEs. The authors conclude that these findings support the safety and clinical efficacy of combining topical IMQ with local RT for recurrent breast cancer, with evidence of local and occasional systemic antitumor activity.