Sequential Moderate Hypofractionated Boost in Breast Cancer Patients: A Monoinstitutional Analysis of Late Side Effects.

Background/aim: In breast cancer (BC) patients who have received breast-conserving surgery, moderate hypofractionation is standard of care for whole-breast irradiation (HF-WBI). On the other hand, the fractionation schedule for the boost is less well defined. A previous prospective study of our group aimed at evaluating acute and late cutaneous and subcutaneous side effects related to a sequential hypofractionated boost (HB) in patients who had received HF-WBI. The present study aimed at evaluating late side effects at a longer follow-up.

Patients and methods: From 2014 to 2015, 219 BC patients received moderate HF-WBI (42.4 Gy in 16 fractions) at the Radiation Oncology Section of the University of Perugia. Patients with negative prognostic factors received a HB (2.65 Gy for 4 or 5 fractions). Late side effects were assessed using the Common Terminology Criteria for Adverse Events v5.0. Univariate and multivariate analyses estimated predictive factors for late toxicity.

Results: Median follow-up was 8.6 years (range=6.7-9.6). One hundred and sixty-five patients were evaluable in the present analysis; HB was administered to 47.3% of them. Late cutaneous and subcutaneous side effects occurred in 26/165 patients (15.8%); and all were G1. In univariate analysis ≥10 excised lymph nodes and HB administration emerged as risk factors for late side effects (p=0.003 and p=0.041, respectively). In multivariate analysis only ≥10 excised lymph nodes were confirmed as a risk factor for side effects (OR=3.431; 95%CI=1.209-9.737).

Conclusion: HB after HF-WBI was safe and well-tolerated, even at a long-term follow-up; consequently, it can be used in routine practice.