Rising Thyroid Cancer Incidence in Southern India: An Epidemic of Overdiagnosis?

Background Thyroid cancer incidence is rising in high-income countries. This increase in disease burden is attributed to the phenomenon of overdiagnosis. Objective We aimed to investigate trends in thyroid cancer rates in India, focusing on the state of Kerala in southern India, which has reported a high incidence of the disease. Design Population-based study using data from the National Cancer Registry Program. Participants We used data from the Population Based Cancer Registries for Thiruvananthapuram (capital of Kerala state), Delhi, Mumbai, Bangalore, and Chennai. We used data for three reporting periods from 2005 to 2014 (represented as 2006, 2009, and 2012). Main Outcome Measures We reported the age-adjusted incidence rate (AARi) and mortality rate (AARm) per 100,000 women and the proportion of thyroid cancers diagnosed in females per 100 cancer cases. Results During 2006, the AARi for thyroid cancer in women in Thiruvananthapuram was 6.9 per 100,000, rising to 10 in 2009 and 13.3 in 2012. There was a 93% increase in incidence rates over less than a decade. The AARis in the other four cities were stable. In 2012, Thiruvananthapuram had at least a fourfold higher incidence compared with other regions. Thyroid was the primary site in one of every 10 cancers diagnosed in Thiruvananthapuram, and large numbers of patients were <40 years of age. The AARm remained stable in all regions. Conclusion We reported a high burden of thyroid cancer in Kerala, India, which is most likely due to overdiagnosis.