Background: 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.
Cases: 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.
Conclusion: 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.