Invasive micropapillary carcinoma of the breast metastatic to the urinary bladder and endometrium: diagnostic pitfalls and review of the literature of tumors with micropapillary features.

Carcinomas with micropapillary features have been described in the breast, urinary bladder, lung, and ovary. They are characterized by the presence of micropapillary tufts in clear spaces. Unequivocal vascular invasion is usually present at the periphery of the tumor. Consequently, these tumors have a high propensity for lymph node metastases and high-stage disease. The metastatic carcinoma can consist exclusively of the micropapillary component, which may elicit an erroneous diagnosis if located in the bladder or lung, as in the patient presented herein. We present a case of a 59-year-old woman with a history of bilateral breast carcinoma status post-bilateral mastectomy, chemotherapy, and tamoxifen therapy. She presented with urinary frequency, and a pelvic mass was noted. A biopsy of the endometrium revealed a poorly differentiated carcinoma. Urinary bladder biopsies showed a carcinoma with micropapillary features diagnosed as micropapillary transitional cell carcinoma. She presented to M.D. Anderson Cancer Center (Houston, TX) for further treatment recommendations. The urinary bladder and endometrial biopsies both contained carcinomas with micropapillary features. The mastectomy specimen showed an invasive ductal carcinoma with a significant micropapillary component. The tumor cells from the breast, endometrium, and urinary bladder were positive for cytokeratin (CK) 7 and estrogen receptor and negative for CK20. In view of the morphologic and immunohistochemical profile, the carcinoma in the endometrium and urinary bladder were interpreted as metastatic lesions from the breast primary. Carcinomas with a micropapillary component are morphologically identical in the breast, urinary bladder, and lung. However, micropapillary serous carcinoma has a different appearance more akin to borderline tumors of the ovary. Immunohistochemical stains are useful in distinguishing these lesions in that thyroid transcription factor-1 positivity suggests a lung primary, CK7 and estrogen receptor suggest a breast primary, and both CK7 and CK20 positivity suggest a urinary bladder primary. It is important to exclude metastatic carcinomas with micropapillary features before making a definite diagnosis of a primary tumor. Carcinomas with micropapillary features have a propensity for lymph node metastases and advanced stage disease. This article discusses the differential diagnosis of carcinomas with micropapillary features in different organs.