Expression of calretinin in high-grade hormone receptor-negative invasive breast carcinomas: correlation with histological and molecular subtypes

Calretinin expression has been reported in neoplasms arising in various organs, including the breast. We investigated the relationship of calretinin expression with different histological and molecular subtypes of invasive breast carcinomas (IBCs) and its prognostic significance in high-grade female hormone receptor-negative IBCs. A total of 196 cases of IBCs of different histological subtypes were analyzed for immunohistochemical expression of calretinin, human epidermal growth factor receptor 2 (HER2), basal-like (BL), apocrine, and proliferative markers and grouped in different molecular subtypes. We found significant morphological differences in the group of formally classified invasive ductal carcinoma of no special type (IDC-NST), which we further subdivided into two types (type I IDC-NST and type II IDC-NST) according to their morphology. Calretinin expression was found in 55.1% of the IBCs and was strongly associated with carcinoma with medullary features (P = 0.014) and type II IDC-NST (P < 0.001), while type I IDC-NST correlated (P < 0.001) with a lack of calretinin expression. Among the molecular subtypes of IBC, calretinin expression was identified in a significant portion of BL breast cancers (BLBCs), while expression was poor in HER2-overexpressing and molecular-apocrine (MA) HER2-negative subtypes and even less in MA/HER2+ ones. Calretinin expression was significantly associated with high (≥50) Ki-67 (P = 0.02), but not with parameters like age, tumor size, lymph node status, overall survival (OS), and disease-free survival. Calretinin expression is most common in high-grade IBCs with histological medullary features, type II IDC-NST and BL phenotype, and is associated with high neoplastic proliferative index.