Risk factors for second primary malignancies following thyroid cancer: a nationwide cohort study.

Objective: Thyroid cancer survivors have a high risk of second primary malignancies (SPMs). We aimed to evaluate the site-specific incidence, prognosis, and risk factors for metachronous SPMs following thyroid cancer. Design: A nationwide cohort study. Methods: This study included data from the Korea National Health Insurance Service (between 2002 and 2018). Exposure to diagnostic radiation was defined by the number of computed tomography (CT) and positron emission tomography-CT scans after the index date. A cumulative radioactive iodine (RAI) dose >100 mCi was considered high-dose RAI. Results: During the median 6 years of follow-up, among 291 640 patients, 13 083 (4.5%) developed SPMs. Thyroid cancer survivors had a 26% increased risk of SPMs compared with the general population (standardized incidence ratio: 1.26; 95% CI: 1.22-1.29). Furthermore, those with SPMs had a significantly poorer survival rate than those without SPMs (hazard ratio: 11.85; 95% CI: 11.21-12.54; P < 0.001). Significantly elevated risks were observed in myeloid leukemia and 13 solid cancer sites: lip, salivary gland, small intestine, larynx, lung, mediastinum and pleura, mesothelium, breast, corpus uteri, ovary, prostate, kidney, and bladder. Frequent diagnostic medical radiation exposure and high-dose RAI therapy were independent risk factors for several SPMs, including the cancer of salivary gland, lung, mediastinum and pleura, breast, kidney, and bladder, as well as myeloid leukemia. Conclusions: Frequent diagnostic radiation exposure and high-dose RAI therapy are independent risk factors for SPM following thyroid cancer. Clinicians need to consider minimizing unnecessary diagnostic radiation exposure and administering a high dose RAI only when justified in patients with thyroid cancer.

Prevalence of BRAFV600E Mutation in Follicular Variant of Papillary Thyroid Carcinoma and Non-Invasive Follicular Tumor with Papillary-Like Nuclear Features (NIFTP) in a BRAFV600E Prevalent Area.

BACKGROUND: BRAFV600E mutation status and prevalence of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) has not yet been reported in Korea. The aim of this study was to investigate the significance of the BRAFV600E mutation in the follicular variant of papillary thyroid carcinoma (FVPTC) and to determine the prevalence of NIFTP in BRAFV600E mutation-prevalent Korean patients. METHODS: This study retrospectively analyzed 1,417 consecutive patients who underwent total thyroidectomy with routine prophylactic central lymph node dissection for papillary thyroid carcinoma (PTC). BRAFV600E mutation analysis was performed routinely using multiplex polymerase chain reaction by applying dual priming oligonucleotide. Clinicopathological characteristics and ultrasonographic findings were compared between BRAFV600E mutation-positive and -negative groups for FVPTC. Pathologists reviewed the pathology slides according to consensus diagnostic criteria for the encapsulated FVPTC and NIFTP. RESULTS: The prevalence of the BRAFV600E mutation in all subtypes of PTC was 61.0% (861/1,411). FVPTC presented a BRAFV600E mutation rate of 27.3%. The FVPTC patients with BRAFV600E mutation were older than those with no BRAFV600E mutation (P = 0.021). The prevalence of NIFTP was 0.18% among all PTC patients (2/1,411) and the proportion of NIFTP among FVPTC was 9.1% (2/22). CONCLUSION: The BRAFV600E mutation is prevalent in Korean patients with FVPTC in a region with high frequency of the BRAFV600E mutation and very low prevalence of NIFTP compared with that reported in western studies.