Abstract P1-15-06: Lobular histology and partial breast irradiation: To what extent is it a cautionary parameter?
Authors: Leonardi Maria Cristina , Maisonneuve Patrick , Morra Anna , Rotmensz Nicole , Dicuonzo Samantha , Lazzari Roberta , Dell'acqua Veronica , Cattani Federica , Mastropasqua Mauro , Luini Alberto , Orecchia Roberto 
Published: May 2015

Abstract
Aim: The high likelihood of multicentricity and multifocality linked to lobular histology (ILC) has called into question the partial breast irradiation. Patients with ILC are categorized in the cautionary group according to ASTRO guidelines. We looked into the population treated with intraoperative radiotherapy with electrons (ELIOT) as full dose to investigate the impact of lobular compared to ductal histology (IDC) in terms of local recurrence.
Matherials and methods: From 1999 to 2007, 2220 patients were treated with breast conserving surgery and intraoperatory radiotherapy with electrons ( 21 Gy at 90% isodose) as sole treatment. The study population includes both patients treated outside and inside the clinical randomized phase III trial ELIOT. Out of 2220 patients, 255 (11.5%) presented ILC. We compared this group with patients having IDC, treated in the same period. The rate of local recurrences has been analyzed, with a minimum follow-up of 5 years. The role of patients and tumor features on local control has been evaluated.
Results: Compared to IDC group, patients with ILC were older (≥ 70, 20% vs. 11%), with no lymph node involvement( pN0, 79% vs. 70%), low grading( G1-2,86% vs.72%), absence of vascular invasion( 81% vs. 98%), higher hormonal receptor status (ER +, 97% vs. 88%), HER2 negativity (96% vs. 89%), low proliferative index( Ki-67, 23% vs. 44%). No differences were noticed with regard to the technical parameters of ELIOT. On the whole, the incidence of local relapse was 4.5% at 5 years (0.9/100 per year). Within the first 5 years of follow-up, no differences were observed between lobular and ductal histology, but after 5 years the difference became significant (p 0.05). Higher risk of local relapse was also observed in old patients ( over 60) with ILC. Regarding the biomolecular classification, lobular carcinomas belonging to Luminal A subtype had a more aggressive local behavior than Luminal A ductal carcinomas, showing a significantly higher rate of local relapse (p 0.0021).
Conclusion: In spite of a favorable tumor profile, a greater incidence of local relapse occurred in tumors with ILC compared to ductal histology. When considering the anagraphic, histological and biomolecular variables, the old age (&gt;60), the proliferative index and the luminal A subtype turned out to be significant. Interestingly, the incidence of local relapse becomes statistically significant 5 years after the treatment. This event points out the importance of an adequate follow-up length, especially in lobular histology for which other reports on whole breast irradiation in literature describe similar biological behavior .
Citation Format: Maria Cristina Leonardi, Patrick Maisonneuve, Anna Morra, Nicole Rotmensz, Samantha Dicuonzo, Roberta Lazzari, Veronica Dell'acqua, Federica Cattani, Mauro Mastropasqua, Alberto Luini, Roberto Orecchia. Lobular histology and partial breast irradiation: To what extent is it a cautionary parameter? [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-06.