Clinical diagnosis and treatment of familial medullary thyroid carcinoma caused by a p.C618Y RET proto-oncogene mutation in a Chinese pedigree

Abstract

To explore the clinical characteristics, therapeutic and clinical significance for RET proto-oncogene screening in a pedigree with familial medullary thyroid carcinoma. Comprehensive medical history was obtained from 19 members in a 4-generate southern Chinese family. Systemic clinical investigations including biochemical testing, imaging examinations and germline RET screening. RET screening showed heterozygous missense mutations of TGC to TAC at codon 618 on exon 10 in 8 cases (p.C618Y) completely consistent with the clinical manifestations. The clinical data of 7 patients with medullary thyroid carcinoma (MTC) and 2 carriers of asymptomatic RET mutation from were analyzed. Single/bilateral multi-centric MTC with lymph node metastases was confirmed in 6 cases by histopathology and 1 case by clinical examination. There were 1 male and 6 females with an initial mean diagnostic age was 49.6 years (range: 24 - 78). All had palpable neck masses. And the mean maximum diameter of MTC was 2.6 cm (range 1.4 - 4.4). Seven patients underwent thyroidectomy except a 78-year-old female patient: right total and left subtotal thyroidectomy (n = 1), right total thyroidectomy (previous left total thyroidectomy for benign mass) (n = 1) and total thyroidectomy (n = 4) were performed. All procedures were accompanied by at least bilateral level VI lymph node dissection and/or with modified single/bilateral neck dissection. After the first operation, 6 patients still presented a high value of calcitonin: 1 patient died of metastasis 64 months postoperatively; 3 patients underwent reoperation at 6 months after initial operation, the calcitonin levels dropped to normal in 2/3 cases and stayed higher in 1 case; another two cases presented bilateral thyroid gland residua, local lymph node enlargement on imaging examination and elevated levels of calcitonin at 214 and 60 months postoperation respectively. However, 1/2 asymptomatic with elevated pre-operative calcitonin subjects underwent total thyroidectomy and histopathological examination showed bilateral C cell hyperplasia. The other carriers, without surgery, with normal neck images, close monitoring and a 10-month follow-up, still presented undetectable calcitonin. Based on family survey, integrated RET screening and serum levels of calcitonin facilitate an early diagnosis and normalize surgery to improve the prognosis. For asymptomatic RET mutation carriers, their levels of calcitonin shall guide the individualized regimen of prophylactic thyroidectomy or strict monitoring and follow-ups.