Impact of molecular subtype on 1325 early-stage breast cancer patients homogeneously treated with hypofractionated radiotherapy without boost: Should the indications for radiotherapy be more personalized?

Aim: We report molecular subtype impact on 1325 early breast cancer (BCa) patients treated with whole breast hypofractionated (WBH) adjuvant forward-planned intensity modulated radiotherapy (F-IMRT) without boost.
Methods and Materials: From 02/2009-05/2017 1325 patients with pTis-pT3, pNx-N1aM0 BCa who underwent breast conservation surgery were treated with WBHF-IMRT in our institute, to a total dose of 40 Gy/15 fractions, without boost. Median age: 62 (interquartile range-IQR-:51.14-70.53) years.
Histology: 8% in situ carcinoma (ISC), 92% invasive tumors. Molecular subtypes (invasive tumors): 49.9% Luminal A, 33.1% Luminal B Her2 negative (-), 6.2% Luminal B Her2 positive (+), 3.6% Hormone Receptor (HR)- Her2+, 7.1% Triple negative (TNBC), and 0.2% HR+. Chemotherapy (CT) was prescribed in 28% of patients, hormonal therapy in 80.3%, monoclonal antibodies (MAb) in 86.8% of Luminal B Her2+ and 97.7% of HR- Her2+ patients.
Results: Median follow up was 72.43 (IQR: 44.63-104.13) months. The 5-year Kaplan-Meier estimates of local relapse-free survival (LRFS) was 97.8%, regional-(RRFS) 98.6%, loco-regional- (LRRFS) 96.9%, distant- (DRFS) 96.6%, disease-free survival (DFS) 94.8% and overall survival (OS) 95.5%. Considering molecular subtypes, 5-year LRFS was: 99.8% for Luminal A, 96.7% for Luminal B Her2-, 94.1% for Luminal B Her2+, 87.9% for HR- Her2+, 95.1% for TNBC and 99.1% for in situ carcinoma.
Conclusion: While the overall estimated probability of LR within 5 years after WBHF-IMRT without boost is good (2.2%), molecular subtypes have a strong impact, despite MAb therapy in Her2+ patients, and CT for TNBC patients, and could be used as a parameter in deciding the boost prescription.
Competing Interests: Declaration of competing interest Dr. Andrei Fodor reports speaker honoraria from Accuray (AERO Academy) and Janssen (Janssen Academy); personal fees for Advisory Board from Sandoz Italia, and reimbursement for travel and accommodations for congresses from Ipsen, AB Medica, Astellas, unrelated to this work. Prof. Dr. Nadia Gisella Di Muzio reports speaker honoraria from Accuray (AERO Academy) and travel and accommodation for a congress from Ipsen, unrelated to this work. Dr. Giampaolo Bianchini reports Consultancy/Advisory role for Roche, Pfizer, AstraZeneca, Lilly, Novartis, Amgen, MSD, Chugai, Sanofi, Daiichi Sankyo, EISAI, Exact Sciences, Neopharm, unrelated to this work. All the other authors have nothing to disclose. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
(Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)