Inherited medullary microcarcinoma of the thyroid: a study of 11 cases.

The authors report 11 patients with genetically determined medullary microcarcinomas. Nine patients were either children or adolescents and two patients were young adults. The youngest patient was 7 years old and the oldest was 34 years of age (mean age, 15.4 yrs). The preoperative diagnosis was based on family history and elevated serum calcitonin levels. In addition, six patients had RET protooncogene mutations in exons 10, 11, and 16. Two patients who had the RET protooncogene mutations did not have serum calcitonin measurements. Nine patients had bilateral medullary microcarcinomas (<1.0 cm), whereas the two patients with unilateral tumors demonstrated multifocal disease. The principle microscopic differences between these genetically determined medullary microcarcinomas and larger sporadic (>1 cm) medullary carcinomas were the low incidence of stromal desmoplasia and amyloid deposition, the high incidence of C-cell hyperplasia, and the low incidence of lymph node metastases. Only one patient, a 34-year-old man, presented with lymph node metastases. All patients remain disease free 11 to 70 months after diagnosis. This small series of thyroid microcarcinomas illustrates the impact molecular diagnostics is having on the management and prognosis of genetically determined medullary carcinoma.