RET genetic screening of sporadic medullary thyroid cancer (MTC) allows the preclinical diagnosis of unsuspected gene carriers and the identification of a relevant percentage of hidden familial MTC (FMTC).

OBJECTIVE: This study was aimed to demonstrate the clinical benefits of rearranged during transfection (RET) genetic screening in patients with apparently sporadic medullary thyroid cancer (MTC) not only to identify the hereditary nature of the disease in the index case but also to discover family members harbouring the same germline mutations (i.e. gene carriers) who are unaware of their condition.

CONTEXT: RET genetic screening allowed the identification of germline RET mutations in apparently sporadic MTC resulting in their re-classification as hereditary forms.

PATIENTS AND MEASUREMENTS: RET genetic screening was performed in 729 apparently sporadic MTC patients by direct sequencing RET exons 5, 8, 10, 11 and 13-16. Clinical and biochemical evaluation of gene carriers was also performed.

RESULTS: We discovered an unsuspected germline RET mutation in 47 of 729 (6·5%) apparently sporadic MTC who were re-classified as hereditary. We found 60 of 146 (41·1%) gene carriers, 35 of whom had biochemical or clinical evidence of MTC. Thirty gene carriers underwent total thyroidectomy and 27 of 30 (90%) were persistently cured after a mean follow-up of 6·0 years. As a further result of RET genetic screening, we observed a significantly higher prevalence of familial medullary thyroid cancer (FMTC) in our series with respect to the largest series of the International RET Consortium (P = 0·0002).

CONCLUSIONS: RET genetic screening of patients with apparently sporadic MTC represents a major tool for the preclinical diagnosis and early treatment of unsuspected affected family members and allows the identification of a relevant percentage of hidden FMTC.