Metastatic carcinoma to the testis: a clinicopathologic analysis of 26 nonincidental cases with emphasis on deceptive features.

Metastatic carcinomas to the testis may simulate primary testicular neoplasms, even in patients with known extratesticular primaries, but information on this topic is limited. We therefore reviewed our experience with 26 cases from consultation (N=23) or hospital (N=3) files; none of the cases were from autopsy material or incidentally discovered in therapeutic orchiectomies from patients with prostate cancer. The tumors occurred in men 29 to 90 years old, with the prostate the most common primary site (N=11), followed by the renal parenchyma (N=4), colon (N=4), urinary tract (N=3), lung (N=2), esophagus (N=1), and, most probably, small intestine (carcinoid, N=1). Noteworthy findings included: the frequent absence of a known primary tumor (62%), the rarity of bilateral involvement (8%), the occasional lack of a distinct mass on gross examination (15%), the infrequency of multinodularity either grossly (8%) or microscopically (35%), the prominence of intertubular growth (42%), conspicuous intrarete or intratubular growth in some cases (especially prostate carcinoma) (19%), prominent cytoplasmic vacuoles in occasional cases (15%), and the frequent presence of lymphatic involvement (69%). Four tumors (3 prostate, 1 renal) with prominent intrarete and/or intratubular growth had submitting diagnoses of either a primary rete neoplasm or seminoma. Four tumors (2 prostate, 1 renal, and 1 bladder) with prominently vacuolated pale cells simulated Sertoli cell tumor. We conclude that, if autopsy cases and incidental tumors in therapeutic orchiectomy specimens are excluded, metastatic carcinomas to the testis are usually solitary, unilateral tumors that may simulate primary neoplasms, including rete adenocarcinoma and Sertoli cell tumor. Despite the rarity of documented cases in the literature, the bladder and renal pelvis should not be overlooked as possible sources for testicular metastasis. The pathologist must have a high index of suspicion for the possibility of a metastatic carcinoma to the testis for any testicular tumor where the routine light microscopic or immunohistochemical findings are unusual for a primary neoplasm. Clues to the likely primary site can usually be gleaned from the pathologic findings.