Syncytial sheets of malignant epithelial cells surrounded by a uniformly dense lymphoid population.
Pleomorphic tumor cells with prominent nucleoli are characteristic of medullary carcinoma.
This other example shows a nicely demarcated outer tumor border overlying lymphoid infiltrate containing the neoplastic cells.
The cells are again synctial in their growth, with nuclear atypia.
Medullary carcinoma belongs to the basal-like mammary carcinomas, which are characterized by "triple-negative" expression of ER, PR and Her2 as well as expression of basal cytokeratins (CK 5/6, CK17, CK14, EGFR). Although triple-negative and basal-like tumors are not synonymous, there is considerable overlap and 60-90% of triple-negative tumors have a basal-like phenotype and they share similar histologic features (Marginean).
Features seen in medullary carcinoma include pleomorphic cytology, high mitotic activity, a circumscribed border, syncytial growth and prominent lymphocytic infiltrate. According to Marginean et al (2010), two features (syncytial growth and prominent inflammation) are associated with improved prognosis.
Patients with BRCA1 mutations (familial breast cancer) exhibit medullary-like features as well, but tend to have a worse prognosis (Fletcher).
Most basal-like or triple negative mammary carcinomas carry a poor prognosis, however, medullary carcinomas appear to be an exception. Medullary carcinomas have a better prognosis compared to other high grade mammary carcinomas.
→Medullary carcinoma is placed under the category of triple-negative or basal-like mammary carcinomas.
→Although triple-negative carcinomas and basal-like mammary carcinomas are not synonymous, but they share many of the same features including ER, PR and Her2 negativity as well as histologic features.
→Compared to most basal-like/triple-negative carcinomas, medullary carcinomas with a syncytial growth pattern and prominent inflammatory infiltrate tend to have an improved prognosis.
→BRCA1 breast cancers also are basal-like and hence, medullary carcinoma-like as well. However, BRCA1 breast cancers have additional histologic and clinical features and BRCA1 breast cancers have a poor prognosis.
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 935-6.
Marginean F, et al. Histological features of medullary carcinoma and prognosis in triple-negative basal-like carcinomas of the breast. Modern Pathology (2010) 23, 1357-1363.