Spindle Cell Lesions of the Breast on Fine-Needle Aspiration Biopsy: A Miscellany of Masses

A variety of primary breast and metastatic lesions to the breast can present with spindle cell cytomorphology. These lesions may range from benign reactive or inflammatory lesions to high-grade malignancies. Spindle cell lesions of the breast are not often seen on fine-needle aspiration biopsy (FNAB) but need to be correctly managed when they are encountered. While mesenchymal lesions of the breast have a spindle morphology, lesions derived from the epithelium and myoepithelium can be spindled as well. By assessing if the lesion comprises spindle cells only or if other components such as epithelial cells are apparent and then determining whether the spindle cells appear bland or pleomorphic, together with close clinicoradiologic correlation and prudent use of ancillary tests, a variety of lesions can be diagnosed on FNAB. However, core needle biopsy or excision biopsy may be required in some patients. The cytomorphology, ancillary studies, and clinicoradiologic findings of a range of spindle cell lesions of the breast are further discussed.