Medullary breast carcinoma: a pathogenic review and immunohistochemical study using tissue microarray.

Introduction: Medullary breast carcinomas (MBCs) are distinguished by circumscribed, high-grade morphology with dense chronic inflammation; they are associated with the basal phenotype but have a relatively good prognosis.

Methods: This study aimed to review the clinicopathological features of MBCs diagnosed at the Department of Pathology, Singapore General Hospital and correlate them with immunohistochemical expression of hormonal markers and c-erbB-2, the basal markers p53, cytokeratin (CK) 14, epidermal growth factor receptor (EGFR) and 34BE12, and the follow-up outcome.

Results: Using Ridolfi's criteria for histologic reviews, 62 patients previously diagnosed as having 'typical MBC' (n = 26), 'atypical MBC' (n = 32) and 'invasive carcinoma with focal medullary-like features' (n = 4) were re-classified as follows: 'typical MBC' (n = 6; 9.7%), 'atypical MBC' (n = 46; 74.2%), and 'non-medullary infiltrating carcinoma' (n = 10; 16.1%). Clinicopathological parameters, including ethnicity, age, tumour size and concurrent ductal carcinoma in situ (DCIS), showed no statistically significant correlation with review diagnoses and immunohistochemical findings. Presence of lymphovascular invasion and nodal stage were significantly correlated with recurrence and breast cancer-related deaths, respectively. ER negativity was significantly correlated with triple positivity for basal markers CK14, EGFR and 34BE12, which comprised patients who showed a significantly decreased disease-free survival rate within a 10-15-year follow-up period.

Conclusions: Lymphovascular invasion and high nodal stage as well as triple negativity among typical and atypical MBCs that have basal-like phenotype represent a portion of invasive carcinomas with medullary features that may have poor outcomes in this otherwise relatively good prognostic group.