Abstract P6-05-06: Incidence and molecular phenotype of multifocal invasive breast carcinomas; A UK multi institutional series
Authors: Shaaban AM , Kaptanis S , Danial I , Smith S , Bradley S , Fernandez S , Mitsopoulos G , Ryan D , Winters Z , Jones L 
Published: May 2016

Abstract
Introduction: Historically, multiple synchronous breast cancers are defined as multifocal (MF) when they aoccur in the same quadrant of the breast, and multicentric (MC) they are in different quadrants; a number of authors continue to use this distinction. Multifocality has been reported to be an independent prognostic factor for survival and local recurrence. The molecular implications of MF and MC versus univocal breast cancers remain to be defined. We sought to investigate the incidence and molecular basis for this phenomenon.
Materials and methods: Following a systematic review of the literature, breast cancer excisions reported by three specialist centers between 2005 and 2014 were investigated (n=4409 cases). Within this cohort, cases identified radiologically and confirmed histologically as mutifocal/multicentric were identified. Data on age at presentation, histological features and molecular profile were collected and compared between MF/MC breast cancer and the unifocal disease. Chi square test was used to compare categorical groups for ER, PR, HER2 and student t-test for mean age comparison. A p-values of ≤ 0.05 was considered significant.
Results: 446 cases (10.12%) were reported as MF/MC invasive breast cancer. Most cases were treated by mastectomy. The majority of these were early breast cancer (Stage 1, 59.1% pT1(m), 72.2% pN0-1). Compared with unifocal breast cancer, patients with multifocal breast cancer were significantly younger (56.6 vs 59 years old, p=0.004) and more likely to have lymph node metastasis on presentation (50% vs 32%, p=0.001). There were differences, some significant, in the molecular profiles of unifocal cancers vs the largest focus of multifocals (ER positive: 80% vs 84% p=0.239, PR positive: 72% vs 76% p=0.301, HER2+ negative: 89% vs 76% p=0.002).
Discussion: A significant proportion (one tenth) of breast cancer presented as multifocal disease. Differences in the immunohistochemical profile, in particular HER2 status, between MF and unifocal breast carcinomas are identified. Both the literature review and analysis of our available cases demonstrated a paucity of data on the incidence, degree of intratumor heterogeneity of multifocal breast cancers and its appropriate management. There are important questions unanswered about the molecular classification of multifocal breast cancer. Future genomic testing of those cases may highlight more pronounced differences. The findings form basis of a biomarker driven trial in set up comparing conservative surgery and mastectomy (MIAMI).
Citation Format: Shaaban AM, Kaptanis S, Danial I, Smith S, Bradley S, Fernandez S, Mitsopoulos G, Ryan D, Winters Z, Jones L. Incidence and molecular phenotype of multifocal invasive breast carcinomas; A UK multi institutional series. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-05-06.