Fine needle aspiration cytology of invasive micropapillary carcinoma of the breast. A case report

BACKGROUND: Invasive micropapillary carcinoma of the breast is uncommon and was characterized only recently. Awareness of this entity and its cytologic appearance is important to allow early diagnosis by fine needle aspiration cytology (FNAC). To our knowledge, only two cases of FNAC of this lesion have been reported in the English-language literature. CASE: An 80-year-old female presented with a firm, nontender mass in the upper outer quadrant of the left breast. FNAC showed ductal carcinoma, and mastectomy showed invasive micropapillary carcinoma. The patient had axillary metastases and received tamoxifen. CONCLUSION: The cytologic features of invasive micropapillary carcinoma are distinctive, with clusters of cells showing hyperchromatic, irregular and crowded nuclei and peripherally located cytoplasm with a rare central lumen. Fibrovascular cores are absent. Although FNAC experience with this lesion is limited, the characteristic cytologic features, including "inside-out" cell clusters, should raise the suspicion of this variant of ductal carcinoma. Differentiation from other papillary lesions and malignancies may be possible, but more experience is needed as the number of reported cases remains limited.