Bilateral testicular metastases of medullary thyroid carcinoma in an adult male with multiple endocrine neoplasia 2A syndrome: case report and review of literature

INTRODUCTION: Medullary thyroid cancer (MTC) is a rare endocrine tumor, which can be sporadic or familial, as a component of multiple endocrine neoplasia 2 (MEN2). Overall, 10% of MTC cases have already developed at presentation or will develop metastasis during follow-up. Testicular metastases are exceptional and only one case of unilateral testis involvement by metastatic MTC has been already reported in literature. We described the first known case of asymptomatic bilateral testicular MTC metastases, discovered incidentally at testicular ultrasound (US) performed for unrelated reasons. CASE PRESENTATION: A Latin American 32-year-old man with MEN 2A syndrome and metastatic MTC underwent andrological and urological examination due to premature ejaculation. US imaging showed two symmetrical hypoechoic lesions involving both testes. Suspecting a bilateral testicular cancer, the patient underwent excision biopsy of both testicular lesions. Histopathology and immunohistochemical examinations documented metastatic MTC of both testicular lesions. CONCLUSION: Beyond its rarity, testis should be considered as a potential metastatic site of MTC, especially in patients with advanced disease. ESTABLISHED FACTS: Distant metastases are present at the diagnosis in 10–15% of patients with medullary thyroid carcinoma (MTC). Testicular metastases are anecdotal. Only one case of unilateral testis involvement by metastatic MTC has been reported in the literature. NOVEL INSIGHTS: Testis should be considered as a possible site of metastases in patients with diffuse metastatic MTC. Testicular ultrasound could be considered as an useful tool for the evaluation and follow-up of metastatic MTC.