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Thyroid hormones are involved in the development and maintenance of virtually all tissues. Although for many years the testis was thought to be a thyroid-hormone unresponsive organ, studies of the last decades have demonstrated that thyroid dysfunction is associated not only with abnormalities in morphology and function of testes, but also with decreased fertility and alterations of sexual activity in men. Nowadays, the participation of triiodothyronine (T3) in the control of Sertoli and Leydig cell proliferation, testicular maturation, and steroidogenesis is widely accepted, as well as the presence of thyroid hormone transporters and receptors in testicular cells throughout the development process and in adulthood. But even with data suggesting that T3 may act directly on these cells to bring about its effects, there is still controversy regarding the impact of thyroid diseases on human spermatogenesis and fertility, which can be in part due to the lack of well-controlled clinical studies. The current review aims at presenting an updated picture of recent clinical data about the role of thyroid hormones in male gonadal function.

Thyroid carcinoma accounts for roughly 1% of all new malignant diseases. Of these, at least 94% are differentiated thyroid carcinoma (DTC), either papillary thyroid carcinoma or follicular thyroid carcinoma. Patients with DTC are usually considered as having a good prognosis, 80% of patients are cured, 20% will develop loco-regional recurrence and 5-10% distant metastasis. However, the disease may have an aggressive course in some patients. The identification of these patients has a major impact in the clinical management of DTC. Several prognostic factors and classification will be addressed, as well the most useful tests for patients follow-up.