Radiotherapy after skin-sparing mastectomy with immediate breast reconstruction in intermediate-risk breast cancer : Indication and technical considerations.

Background: Skin-sparing (SSME) and nipple-sparing mastectomy (NSME) were developed to improve the cosmetic results for breast cancer (BC) patients, both allowing for immediate breast reconstruction. Recommendations for post-mastectomy radiotherapy (PMRT) are primarily derived from trials where patients were treated by standard mastectomies. Due to their more conservative character, SSME and especially NSME potentially leave more glandular tissue at risk for subclinical disease.

Methods: Rates and sites of locoregional failures following SSME and NSME plus/minus reconstruction were analyzed regarding tumor stage and biological risk factors. In particular, the role of PMRT in "intermediate"-risk and early stage high-risk breast cancer patients was revisited. Implications on targeting and dose delivery of PMRT were critically reviewed.

Results: The value of PMRT in stage III BC remains undisputed. For node-negative BC patients, the majority of reports classify clinical and biological features such as tumor size, close surgical margins, premenopausal status, multicentricity, lymphangiosis, triple-negativity, HER2-overexpression, and poor tumor grading as associated with higher rates of locoregional relapse, thus, building an "intermediate" risk group. Surveys revealed that the majority of radiation oncologists use risk-adaptive models also considering the number of coinciding factors for the estimation of recurrence probability following SSME and NSME. Constellations with a 10-year locoregional recurrence risk of >10% are usually triggering the indication for PMRT. There was no common belief that the amount of residual tissue, e.g., tissue thickness over flaps, serves as additional decision aid. Modern treatment planning can ensure optimal dose distribution for PMRT in almost all patients with SSME. There are no reliable data supporting a reduction of the treatment volume from the CTV chest wall, e.g., to the nipple-areola complex, to the dorsal aspect behind the implant volume, the pectoralis muscle, nor the regional interpectoral, axillary, or complete regional lymph nodes only. The omission of a skin bolus in intermediate-risk BC does not compromise oncological safety.

Conclusions: For intermediate-risk as well as early stage high-risk BC patients, the DEGRO Breast Cancer Expert Panel recommends the use of PMRT following SSME and NSME when a 10-year locoregional recurrence risk is likely to be greater than 10%, as estimated by clinical and biological risk factors. Subvolume-only radiation is discouraged outside of trials. The impact of adequate systemic treatment and the value of radiotherapy on optimal locoregional tumor control, with the goal of less than 5% LRR at 10-years follow-up, has to be verified in prospective trials.