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?

• Published in: Breast (Edinburgh) Vol. 55; pp. 45 - 54
• Main Authors: Fodor, Andrei, Brombin, Chiara, Mangili, Paola, Borroni, Fulvio, Pasetti, Marcella, Tummineri, Roberta, Zerbetto, Flavia, Longobardi, Barbara, Perna, Lucia, Dell’Oca, Italo, Deantoni, Chiara L., Deli, Aniko M., Chiara, Anna, Broggi, Sara, Castriconi, Roberta, Esposito, Pier Giorgio, Slim, Najla, Passoni, Paolo, Baroni, Simone, Villa, Stefano L., Rancoita, Paola M.V., Fiorino, Claudio, Del Vecchio, Antonella, Bianchini, Giampaolo, Gentilini, Oreste D., Di Serio, Mariaclelia S., Di Muzio, N.G.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.02.2021; Elsevier
• Subjects: Breast cancer conservative treatment; Breast cancer molecular subtypes; Early stage breast cancer; Hypofractionated whole breast radiotherapy; Original; Tumor bed boost; Hypofractionated whole breast radiotherapy; Breast cancer conservative treatment; Breast cancer molecular subtypes; Early stage breast cancer; Tumor bed boost
• ISSN: 0960-9776; 1532-3080
• DOI: 10.1016/j.breast.2020.12.004

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. 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. 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. 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. •Hypofractionated three-weeks radiotherapy ensures good local control whitout boost.•In 1325 early stage breast cancers 5-year local relapse without boost was 2.2%.•Molecular subtypes have a strong impact on estimated probability of local relapse.•5-year local control (LC) was 99.8% for Luminal A vs 87.9% for HR- Her2+.•5-year LC was 96.7% for Luminal B Her2-, 94.1% for Luminal B Her2+, 95.1% for TNBC.