Thyroid cancer incidence in India between 2006 and 2014 and impact of overdiagnosis.

CONTEXT/OBJECTIVE: Increases of thyroid cancer (TC) incidence emerged in the last decades in several countries. This study aimed to estimate time trends of TC incidence in India and the proportion of TC cases potentially attributable to overdiagnosis by sex, age, and area. DESIGN: TC cases aged 0-74 years reported to Indian cancer registries during 2006-2014 were included. Age-standardized incidence rates (ASR) and TC overdiagnosis were estimated by sex, period, age, and area. RESULTS: Between 2006-2008 and 2012-2014, the ASRs for TC in India increased from 2.5 to 3.5/100,000 women (+37%) and from 1.0 to 1.3/100.000 men (+27%). However, up to a 10-fold difference was found among regions in both sexes. Highest ASRs emerged in Thiruvananthapuram (14.6/100,000 women and 4.1/100,000 men in 2012-2014), with 93% increase in women and 64% in men compared to 2006-2008. No evidence of overdiagnosis was found in Indian men. Conversely, overdiagnosis accounted for 51% of TC in Indian women: 74% in those aged <35 years, 50% at ages 35-54 years, and 30% at ages 55-64 years. In particular, 80% of TC overdiagnosis in women emerged in Thiruvananthapuram, while none or limited evidence of overdiagnosis emerged in Kamrup, Dibrugarh, Bhopal, and Sikkim. CONCLUSIONS: Relatively high and increasing TC ASRs emerged in Indian regions where better access to healthcare was reported. In India, as elsewhere, new strategies are needed to discourage opportunistic screening practice, particularly in young women, and to avoid unnecessary and expensive treatments. Present results may serve as a warning also for other transitioning countries.