TTF-1-positive Metastatic Endometrioid Carcinoma: A Case Report and Review of Literature of a Potential Diagnostic Pitfall.

A 75-year-old female patient, nonsmoker was addressed to our institution for a fracture of C5 vertebra with spinal cord compression by a tumor mass invading surrounding soft tissue. She had a previous history of breast ductal carcinoma and endometrioid carcinoma. Biopsy of the tumor mass showed a TTF-1-positive carcinoma. Molecular study showed a E545K mutation of PIK3CA. Lung imaging showed multiple nodules evocative of metastasis rather than a primitive tumor. Reviewing of slides of endometrioid carcinoma showed areas positive for TTF1, and the same E545K mutation was found in endometrial tumor. The final diagnosis was endometrioid metastatic carcinoma with aberrant TTF-1 expression. A subset of endometrial neoplasm expresses TTF-1, this situation might be confusing especially in case of metastatic disease.