Lung carcinoma with metastasis to testicular seminoma.

Tumor-to-tumor metastases are uncommon. The most frequent donor tumors are the lung, whereas renal cell carcinoma is by far the most common recipient. In this report the authors describe a lung tumor that metastasized to a testicular seminoma. This is the first reported case of tumor-to-tumor metastases in which seminoma of the testis is the recipient. The authors performed mucin and immunohistochemical studies on this case and on ten cases of nonseminomatous germ cell tumors containing embryonal carcinoma and endodermal sinus tumor for comparison. Mucin positivity as well as immunoreactivity for epithelial membrane and carcinoembryonic antigens were confined to metastatic adenocarcinoma in this case, whereas Ki-1 and alpha-fetoprotein immunostaining were restricted to the ten control cases of germ cell tumors. Although the majority of second malignant components found in a seminoma are other nonseminomatous germ cell components, the rare possibility exists that a second malignant component is a metastasis from elsewhere in the body.