Fine-needle aspiration cytology of triple-negative basal-like breast cancer

Invasive breast cancer is divided into luminal A, luminal B, HER2 overexpression, basal-like (BL) and normal-like subtypes, among which the BL subtype has the worst prognosis. The purpose of this study was to determine the clinicopathological and cytological characteristics of BL breast cancer (BLBC). Fine-needle aspiration cytology samples from 17 patients with consecutive BLBC were investigated, and the findings were compared with those of other subtypes (10 cases each) for the following cytomorphological features: necrosis; lymphocyte infiltration; mitotic index; apoptosis; naked nuclei; nuclear/cytoplasmic ratio; nuclear margin, size and pleomorphism; chromatin granularity and density; and nucleolar appearance. Histologically, the BLBCs were heterogeneous, and included medullary carcinoma and metaplastic carcinoma, in addition to invasive ductal carcinoma. Cytologically, high mitotic index, naked nuclei, and irregular nuclear margin were significantly observed when compared with both the luminal A and B subtypes. Large nuclei with nucleoli and lymphocyte infiltration were frequently seen compared with the luminal A and B subtypes, respectively. Squamous nodules were seen in all metaplastic cases, but not in the HER2 overexpression subtype. Lymphocyte infiltration, squamous metaplasia, and nuclear findings such as a high mitotic index, naked or large nuclei, an irregular nuclear margin and the presence of nucleoli, may be clues indicating BLBC.