Fine‐needle aspiration cytology for the diagnosis of solid basaloid adenoid cystic carcinoma of the breast: Its role,limitation, and perspective

Solid basaloid adenoid cystic carcinoma (SB‐AdCC) is a subtype of breast AdCC which shows more aggressive clinical behavior than other subtypes. Fine‐needle aspiration (FNA) cytology is a useful diagnostic tool for breast malignancies. However, most of the diagnostic cytological characteristics of AdCC are not present in SB‐AdCC and cytomorphological studies of this subtype are limited. Here, we evaluated the utility of FNA in the diagnosis of SB‐AdCC of the breast. A search of the pathology archives of our institutions for FNA specimens of histologically confirmed SB‐AdCC between 2012 and 2019 identified four patients with SB‐AdCC of the breast. All patients were female and the average age was 60 years. Cytologically, one case was classified as malignant, two as indeterminate, and one as unsatisfactory. Smears had low to moderate cellularity. All smears showed ribbon‐like material surrounding the clusters and a vertical nuclear arrangement toward the peripheral rim. Hyaline globules appeared only in one case. Cells in all cases showed an oval, angular, and spindle shape hyperchromatic nuclei with mild to severe atypia, and also dispersed naked nuclei similar to the cells of the clusters were detected in one case. In histological sections, these cytological findings were compatible with the histological findings and divergent histological differentiation was detected. Diagnosing of few cellular smears of SB‐AdCC is difficult whereas the features of peripheral rim of the clusters, naked nuclei, and the divergent differentiation may be important for diagnosing SB‐AdCC of the breast.