Many neoplasms secrete the embryonic protein hCG. hCG will crossreact in most immunoassays for LH and, due to its positive detection in hCG-b assays, causes a positive pregnancy test in boys. It stimulates the testes of affected boys to produce testosterone, and incomplete sexual precocity results. Young patients with incomplete precocious puberty may have hCG secreting hepatomas and hepatoblastomas which are often fatal within months of diagnosis (Fig. 13.35). Teratomas or chorioepitheliomas in the hypothalamic or pineal region can also produce hCG and cause incomplete sexual precocity. Such tumours are rare in girls, but even if they occur and produce hCG, no physical changes will result because of the elevated hCG levels. Boys with 47XXY Klinefelter's syndrome have an increased incidence of hCG-secreting mediastinal germ cell neoplasms.
