Fine needle aspiration cytology of lobular carcinoma in situ on ThinPrep

Lobular carcinoma in situ (LCIS) of the breast is a recognized marker for increased risk of invasive carcinoma and has well-established histologic criteria. However, its detection and diagnosis on FNA of breast has not been well defined. Cytology slides (all ThinPrep) of 11 cases with biopsy-proven LCIS at Beth Israel Deaconess Medical Center were reviewed. All 11 cases showed tight and/or loosely cohesive clusters of crowded mildly enlarged nuclei and ten of 11 showed at least moderate cellularity. Single epithelial cells, small but prominent nucleoli, intracytoplasmic lumina, and two distinct epithelial-cell populations were also noted in some cases. As none of these features is specific for LCIS, it would be prudent to report such lesions as atypical so that a core biopsy or excisional biopsy will be performed before definitive treatment. The original FNA diagnosis of the 11 cases ranged from epithelial proliferation without atypia to carcinoma. Three of the 11 cases had fibroadenomas on histology with extensive involvement by LCIS. Since management for LCIS is different from that for invasive carcinoma or DCIS, it should be considered and distinguished from the latter two in cases suspicious for carcinoma on FNA.