[Non-seminomatous testicular cancer presenting with hyperthyroidism].

Thyrotoxicosis caused by human chorionic gonadotropin (hCG) is a rare form of hyperthyroidism, often associated with conditions involving very high levels of hCG and sometimes seen in women with gestational hyperthyroidism. Here we present a case of a 53-year-old man with metastatic non-seminomatous testicular cancer (NSGCT) and concomitant thyrotoxicosis related to extremely high hCG levels. The patient sought care with symptoms such as fatigue, weight loss, nausea, and a distended abdomen. Laboratory work-ups showed thyrotoxicosis with suppressed TSH and elevated levels of free T4 and T3. At the same time, a grossly elevated hCG level of over 100,000 IU/L was detected. Further diagnostics confirmed NSGCT with extensive liver, lung, and lymph node metastases. The patient was treated with chemotherapy, which resulted in rapid reduction of hCG levels and remission of thyrotoxicosis. Thyrotoxicosis induced by hCG should be considered in patients with germ cell tumors and very high hCG levels. Effective treatment of the underlying malignancy can lead to normalization of the thyroid function.