A case of invasive micropapillary carcinoma of the breast

Invasive micropapillary carcinoma (IMP) of the breast is uncommon and has only recently been characterized. Knowing the cytological appearance of IMP is important to enable early diagnosis by fine needle aspiration cytology (FNAC). We describe a case of IMP diagnosed by preoperative FNAC. A 48-year-old menopausal woman presented in 2003 with a mass in her left breast. Mammogram and ultrasound findings indicated that the tumor was malignant. Cytological examination showed papillary clusters of hyperchromatic cells with irregular and crowded nuclei, but lacking papillary cores. No myoepithelial cells were seen. Based on the cytological findings, invasive micropapillary carcinoma was diagnosed. Microscopic findings showed cancer cells with moderate atypia in abundant micropapillary cancer nests without a fibrovascular core. These cancer nests were morula-like, surrounded by empty, clear spaces lined with delicate strands of fibrocollagenous stroma. The polarity of each cancer nest was reversed, with the secretion border facing fibrocollagenous stroma. These pathological features occupied the invasive part of the primary tumor. The cytologic features of IMP are distinctive and correlate with histology. FNAC of IMP is important role to confirm the diagnosis.