Lung adenocarcinoma with micropapillary component presenting with metastatic scrotum tumor and cancer-to-cancer metastasis: A case report.

A 54-year-old man was admitted to the hospital presenting with a 3-month history of sclerosing dermal lesion in the external genitalia. A scrotal skin biopsy revealed a poorly-differentiated adenocarcinoma, immunohistochemically positive for cytokeratin 7 (CK7) and for thyroid transcription factor 1 (TTF-1), and negative for CK20. One month after admission, he died of respiratory failure. At autopsy, a consolidating lesion with vague margin was noted in the left lung as well as a well-circumscribed nodule in the right lobe of the thyroid. Histopathologically, pulmonary lesion was adenocarcinoma with a micropapillary component. On the other hand, thyroid tumor was diagnosed as a follicular variant of papillary carcinoma with foci of micropapillary adenocarcinoma. Positive immunohistochemistry for surfactant protein on micoropapillary component was useful to confirm that micropapillary component was of lung adenocarcinoma origin.