Elevated Risks of Subsequent Primary Malignancies in Patients With Thyroid Cancer: A Nationwide, Population-Based Study in Korea

BACKGROUNDThyroid cancer affects relatively young adults, and its overall survival is excellent. With long life expectancy, the development of subsequent cancers is an important concern for survivors of thyroid cancer. The objective of this study was to investigate the incidence and types of second primary malignancies in Korean patients with thyroid cancer. METHODSThe study cohort included 178,844 registrants with thyroid cancer from the Korea Central Cancer Registry (KCCR) database between 1993 and 2010. Standardized incidence ratios (SIRs) were calculated using a statistical software program (SEER*Stat 8.0.4). RESULTSAmong 178,844 patients with thyroid cancer, 2895 (1.6%) were diagnosed with subsequent second primary malignancies. The overall risks of a second primary cancer were elevated by 6% in patients who had thyroid cancer compared with the general population during the same period. The elevated risks for developing second cancers were observed in all sites except the stomach and cervix. The elevated risk of second primary cancers was observed within the first 10 years of follow-up. Leukemia and cancers of the salivary gland, kidney, prostate, lung, and breast had the most significantly elevated risks as secondary cancers and presented as early as during the first 5 years after the initial diagnosis of thyroid cancer. CONCLUSIONSThis is the largest, standardized, population-based study to date using nationwide data from the entire Korean population. The risks of several cancers were elevated significantly during follow-up, thus alerting physicians to pay special attention in their care of patients with thyroid cancer and long-term survivors. Cancer 2015;121:259-68. (c) 2014 American Cancer Society. In patients with primary thyroid cancer, the risks of several cancers are elevated significantly during follow-up. Thus, physicians are needed to pay special attention in their care of thyroid cancer patients and long-term survivors.