A cohort study on 10-year survival of sporadic medullary thyroid carcinoma with somatic RET mutation

Somatic rearranged during transfection (RET) mutations are reported in 40-50% of sporadic medullary thyroid carcinoma (sMTC) patients with prognostic significance. As there is a lack of somatic RET mutations reported previously for the Taiwanese population, we tried to assess the presence of somatic RET mutations and evaluate the potential outcome predictors for our sMTC patients. We collected data from seven sMTC patients from the years 1997 to 2005 and analyzed their clinic-pathological features up to 2015. All patients were still alive to follow up for 11∼18 years. Tumor DNAs were extracted to assess exons 10-11 and 13-16, and the intron-exon boundaries of the RET gene. Six cases (86%) were screened positive of somatic RET gene mutations in hotspot regions, one at M918T, one at C620R, and three at C634S, with another two rare mutations at L629Q and V642I. Comparing the current tumor, node, metastases staging system, the 10-year survival outcomes for our sMTC patients was not predicted by serum calcitonin and/or carcinoembryonic antigen, surgical extent, and presence of the somatic RET gene mutations. The small cohort demonstrated a relatively good outcome of sMTC patients to survive >10 years. In addition, intensive treatment with total thyroidectomy with extensive neck lymph node dissection seemed to be the critical determinant of better survival outcome for sMTC patients.