Loss of ARID1A expression is associated with poor prognosis in invasive micropapillary carcinomas of the breast: A clinicopathologic and immunohistochemical study with long‐term survival analysis

Invasive micropapillary carcinoma (IMPC) of the breast is a highly aggressive and a rare subtype of breast cancer. In this study, we aimed to investigate differences between pure and mixed IMPCs of the breast in terms of clinicopathologic features, and also to analyze the significance of expressions of ARID1A and bcl‐2 regarding prognosis. Sixty‐nine of IMPCs consisting of 21 pure and 48 mixed type diagnosed at Pathology Department of Istanbul Medical Faculty between 2000 and 2011, who had complete follow‐up data, were collected to analyze ARID1A and bcl‐2 expressions immunohistochemically with prognosis. The median follow‐up period was 94 months. No significant difference was found between pure and mixed type IMPC, as well as in luminal subgroups in terms of prognostic and clinicopatologic features. ARID1A and human epidermal growth factor receptor‐2 (Her‐2) status were found to be independent prognostic factors of both overall survival (OS) (HR=6.1, 95% CI 1.4‐26.6, P=.02; HR=15.9, 95% CI 3.5‐71.5, P<.0001, respectively) and disease free survival (DFS) (HR=4, 95% CI 1.1‐14.9, P=.04; HR=7.2, 95% CI 2‐25.4, P=.002, respectively) in multivariate analysis using Cox regression. The loss of ARID1A expression was significantly related with 10 year‐OS (P=.001) and 10 year‐DFS (P=.05). Statistically significant effect of ARID1A expression was also stated on DFS and OS in Luminal B group (P=.05 and P=.001 respectively). Pure and mixed type IMPCs are similar in terms of clinicopathologic and prognostic features. The loss of ARID1A expression and Her‐2 positivity have significant adverse effect clinical outcomes of IMPC patients.