Failure of pentagastrin-stimulated calcitonin testing in early manifestation of familial medullary thyroid cancer.

This case report describes three generations of a family with familial medullary thyroid cancer (RET gene mutation L790F). One of the three siblings-all of them carrier of the respective mutation-exhibited the absence of pathological basal and pentagastrin-stimulated calcitonin levels in spite of multifocal medullary thyroid microcancer. This case illustrates the challenge to consider the biological diversity of RET gene mutations in the clinical management of affected gene carriers.