Primary systemic treatment and concomitant low dose radiotherapy for breast cancer: Final results of a prospective phase II study

Background: To evaluate the efficacy of preoperative low dose fractionated radiotherapy (LD-FRT) and chemotherapy in breast cancer. Materials and methods: Patients with stage IIA-IIIA breast cancer, received LD-FRT (0.40Gy bid, on day 1 and 2, for 6 cycles) to primary tumor volume and concurrent chemotherapy with non-pegylated liposomal anthracycline and docetaxel. Pathological response was assessed by Mandard Tumor Regression Grade (TRG). We evaluated the pathological major response rate (PMRR) as TRG1 and TRG2. The expected outcome was a PMRR of 60%. The accrual was determined by the single proportion powered analysis (. α=0.05, power=0.8). Results: Twentyone patients were enrolled. No grade 2-4 acute skin and hematological toxicity was observed. TRG1 was obtained in 3 patients (14.3%), TRG2 in 4 patients (19%). The PMRR was 33.3%; it does not concur with the expected result, but is similar to that of chemotherapy alone. According to molecular subtype, 2/11 luminal A patients and 4/6 luminal B patients obtained a PMRR to preoperative treatment (35.3%); 1/4 basal like patients reported TRG1 (25%). Conclusions: LD-FRT concomitant with primary systemic treatment has a good toxicity profile. The response rate is consistent with that of chemotherapy alone, and suggests different interactions between low dose radiotherapy and molecular subtypes. Additional investigations are planned.