Risk estimation and screening in families of patients with medullary thyroid carcinoma.

Many gene carriers for multiple endocrine neoplasia type 2a (MEN 2a) do not manifest the disease, even into old age. Thus, a negative family history in a patient presenting with medullary thyroid carcinoma does not reliably exclude familial disease. Data are reported for the probability that the MEN 2a gene will either have manifested clinically or be detectable by stimulated calcitonin screening by a given age. These probabilities can be used to calculate individual risks and to guide screening.