Hyperthyroidism Associated with Gestational Trophoblastic Neoplasia: Systematic Literature Review and Pathways Analysis.

: Gestational trophoblastic disease (GTD) is a group of disorders including complete, partial, and invasive/metastatic hydatidiform moles, as well as gestational trophoblastic neoplasia (GTN) (choriocarcinoma; placental site trophoblastic tumor, PSTT; epithelioid trophoblastic tumor, ETT; or mixed forms). These entities are characterized by increased trophoblast proliferation, rarely complicated by hyperthyroidism. : Our systematic literature review (PRISMA guidelines; PubMed, Web of Science, and Scopus databases) searched for histologically confirmed cases of GTN associated with clinical or subclinical hyperthyroidism. We described the clinical-pathologic features and the pathways of hyperthyroidism in GTD. : We identified just 32 choriocarcinomas and one PSTT; other non-histologically confirmed cases could have been identified, as some patients received a clinical diagnosis based on serum human chorionic gonadotropin (hCG) levels and imagining data and were treated accordingly. As regards choriocarcinomas, patients' age range was 15-45 (mean 27) years. Metastases involved the lungs (53%), brain (25%), and liver (19%) (less frequently, the kidneys, spleen, ovaries, vagina, pelvis/abdomen, or thyroid). The time to recurrence range was 1-36 (mean 12) months. On follow-up, 10 patients (32%) were alive with disease and 6 (19%) showed no evidence of disease, while most of the women (15 cases, 48%) died of disease. The hCG level range was 10,000-3,058,000,000 (mean 128,957,613) IU/L. At least some symptoms and/or signs of hyperthyroidism were evident with variable intensity in most cases and significantly improved within 2-3 weeks after treatment. : Increased trophoblast proliferation could stimulate thyroid function via increasing the half-life of thyroxine-binding globulin. Secondly, increased hCG demonstrates cross-reactivity with the thyroid-stimulating hormone due to similar α-subunits. Moreover, basic isoforms of hCG may facilitate thyrotropic activity.