Topical TLR7 agonist and radiotherapy in patients with metastatic breast cancer

Toll-like receptor (TLR) agonists and radiation therapy hold promise for cancer immunotherapy. We conducted a phase I/II trial combining topical imiquimod (IMQ, a TLR-7 agonist) and local radiotherapy (RT) in patients with metastatic breast cancer accompanied by longitudinal transcriptional analysis of tumor biopsies.

The primary objective of the trial (NCT01421017) was to assess systemic responses by immune-related response criteria (irRC) after an 8-week cycle of topical IMQ and concurrent local RT (cohort 1). An amendment to the trial added two cohorts, both received one dose of cyclophosphamide (CTX) administered 1 week before study treatment initiation, IMQ/RT/CTX (cohort 2) and RT/CTX control (cohort 3). Cutaneous metastases were prospectively assigned to treatment with IMQ and RT (area A) or IMQ alone (area B). Secondary objectives were safety (Common Terminology Criteria for Adverse Events criteria) and local response in skin metastases. In all IMQ cohorts, tumors were biopsied before treatment and at 2 and 3 weeks.

31 patients were enrolled (n=12, n=12, and n=7, in cohort 1, 2, and 3, respectively), with 4 out of 24 patients in the IMQ cohorts showing systemic tumor responses (two complete responses (CR) and two partial responses (PR)). No objective responses were observed in the seven patients enrolled in the control arm (RT alone). The treatment was well-tolerated, no grade 4-5 treatment-related adverse events occurred and grade 3 AEs were manageable (anemia, local pain, and local ulceration, n=1 each). Local objective responses were observed in 19/24 (9 CR and 10 PR) and 5/24 (5 PR) in areas treated with combined IMQ-RT and IMQ alone, respectively (p<0.001). All 24 patients treated with IMQ underwent serial biopsies, and 84 samples yielded sufficient material for transcriptional analyses. These revealed that the presence of a T-helper 1 functional orientation of the tumor microenvironment paralleled by the downregulation of DNA-repair genes was associated with CR after IMQ+RT, but not after IMQ alone. No post-treatment activation of immune-effector functions was observed in stable and progressing lesions.

Our 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.

NCT01421017.