Metastatic carcinoma involving the testis. Clinical and pathologic distinction from primary testicular neoplasms.

Metastatic carcinoma to the testis is unusual. There are only seven previously reported cases in which a testicular mass was the first clinical manifestation of an underlying malignancy. The authors review 127 cases in which the testis was involved by metastatic carcinoma, and describe an additional two patients in whom a malignant testicular mass was the presenting sign of an underlying nontesticular carcinoma. The tumors most commonly reported to metastasize to the testis are: prostate (45 cases), lung (25 cases), melanoma (12 cases), colon (11 cases), kidney (10 cases), stomach (6 cases), and pancreas (5 cases). Neuroblastoma, retinoblastoma, carcinoid tumor, and cancers of the bile duct, ureter, bladder, salivary gland, and thyroid have also involved the testis secondarily. Nineteen patients (15%) had bilateral testicular metastases. Patients with secondary testicular neoplasms were older in general than those with germ cell tumors (mean, 55 years; median, 57 years). Histologically, the presence of extensive lymphatic and vascular invasion and an interstitial pattern, in which the seminiferous tubules are spared, is suggestive of a metastasis. In four of the nine cases (44%) in which testicular enlargement was the first manifestation of an underlying carcinoma the correct pathologic diagnosis was initially missed. Serum alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) are occasionally elevated in patients with nontesticular primary tumors, but markedly elevated levels in young patients suggest a nonseminomatous germ cell tumor, as does positive immunoperoxidase staining for AFP and HCG.