Fine Needle Aspiration Cytology of Invasive Micropapillary Carcinoma of the Breast

Abstract
Invasive micropapillary carcinoma is a recently described variant of invasive breast cancer characterized by the formation of micropapillae within clear spaces separated by a fibrocollagenous stroma. Although the histologic features are well described, to the best of our knowledge, the cytologic findings have not been reported. The fine needle aspiration cytology of two cases of biopsy confirmed invasive micropapillary carcinoma are described and compared to the histologic features. In one case, an additional FNA of a subsequent metastasis is reviewed. The cytologic features of invasive micropapillary carcinoma are distinctive and correlate with the histology. Invasive micropapillary carcinoma can be suggested based on the FNA findings of numerous well-formed angular, papillary clusters along with other criteria of malignancy. The cytologic differential diagnosis of invasive micropapillary carcinoma is discussed.