National Breast Cancer Surgery Snapshot Study: Breast Cancer Surgery after Neoadjuvant Systemic Therapy in Primary Breast Cancer (MANS Study).

[INTRODUCTION] The use of neoadjuvant systemic therapy (NST) in primary breast cancer has increased worldwide. This study provides real-time data of the reasons and variation in NST, conversion rate of mastectomy to BCS and conversion rate of ALND to radiation or omission of axillary treatment.

[METHODS] This is a Breast Cancer Surgery Snapshot study, multicenter prospective cross-sectional study in 70 breast cancer hospitals in the Netherlands. For 2 months the reason for NST is registered with patient- and tumor characteristics. The expectation of the surgical procedure in breast and axilla before and after NST is noted and the actual surgical outcome after NST is registered.

[RESULTS] Four hundred sixty seven patients receiving NST were registered. The 3 main reasons for NST were in 26% axillary down-staging, 25% a triple negative (TN) tumor and 25% HER2+. Before NST, 219 patients (47%) were eligible for BCS. In 210 patients (45%) initially assigned to receive a mastectomy, 99 patients (47%) underwent BCS. Triple negativity had the highest conversion rate with 68%. Of all mastectomy patients, 30% showed a pCR of the breast. Axillary conversion from ALND to axillary sparing surgery was achieved in 87% cN+ patients.

[CONCLUSION] In the Netherlands the main reasons for NST were subtype (triple negative, HER2+) and axillary down staging. Additional reasons for NST focused more on down staging to convert to BCS and improve cosmetic outcomes. Real time data showed that NST lead to very high conversion rates from mastectomy to BCS as well as high rates of omission of ALND after NST.