A study on the prevalence of HER2 genetic heterogeneity and its impact on breast cancer survival.

Abstract

586 Background: HER2 heterogeneity (GH) has been described in breast cancer that has conventionally been labeled as HER2 negative (FISH score <2.2). We aimed to ascertain the prevalence of GH in HER2 negative breast cancers and to investigate for any impact on survival. Methods: We reviewed HER2 FISH (Vysis) data for 158 primary breast cancer specimens from 2006-2010 which were 0 – 2+ on immunohistochemistry. HER2:CEP17 ratios were calculated for each of the 60 cells scored and cases were classified as HER2 GH according to the ASCO/CAP guidelines (GH = 5-50% tumor cells with a ratio >2.2). Results: 67% (106/158), 7% (11/158) and 26% (41/158) were HER2 negative, equivocal (FISH ratio 1.8-2.2) and positive respectively. GH was found in 43% and 100% of Her2 negative and HER2 equivocal patients respectively. Of the 117 cases (with FISH score <2.2), HER 2 GH was associated with higher histologic grade (grade 3: 81.8%, 52.3% and 33.3% in HER2 equivocal, negative with GH and negative without GH (p = 0.007). There were no significant associations with ER status or the presence of lymphovascular invasion. The mean overall survival was 63 months (95% CI 43-87), 118 months (95% CI 96-141) and 148 months (95% CI 148-168) for HER 2 equivocal, negative with GH and negative without GH patients respectively (p=0.017). In a subset analysis of HER2 negative (with FISH score <2.2), non metastatic patients, with at least a 4 year follow up period (n=63), mean overall survival was 79 months (95% CI 60-98), 119 months (95% CI 96-143) and 159 months (95% CI 139-180) for HER2 equivocal, negative with GH and negative without GH patients (p=0.034). GH remained a significant factor in the multivariate analysis irrespective of grade, stage and ER status (p=0.046). Conclusions: HER2 GH occurs in 100% of HER2 equivocal and 43% of HER2 negative breast cancers and is associated with higher histologic grade and poorer overall survival, irrespective of grade, stage or hormonal status.