Over-diagnosis behind thyroid cancer in Kerala?

Is it some new environmental factor that has suddenly emerged that is making thyroid cancers tick upwards or is it the lasting effect of high-background radiation that one witnesses in Kerala due to the presence of thorium-rich monazite sands? 

Or is it as some anti-nuclear activists suggest that the neighbouring Kudankulam nuclear power plant is to be blamed for the increase in thyroid cancers? 

Thyroid cancers are usually linked to exposure to radiation. Scientists are now suggesting that it is merely a case of over diagnosis since Kerala has some of the finest healthcare facilities in India. So, is an epidemic of over diagnosis the real reason behind an upsurge in cases of thyroid cancer in Kerala? 

This is probably the first case of over-diagnosis reported from India and possibly the first time that the top-class health facilities of Kerala are throwing up a challenge. 

Thiruvananthapuram, the capital of Kerala, has seen almost a doubling of thyroid cancer in women between 2006 and 2012. This comes out even as a report this week suggests that “Amrita Institute’s cancer registry, as many as 8,586 diagnosed thyroid cancers would require medical attention and services in a year in the state while there will be 2,862 newly-diagnosed female thyroid cancer patients every year in the coming decade.” 

This kind of data when compared to thyroid cancers cases in the rest of India seems very alarming. One constant factor that plays in the minds of the lay population is the presence of high-background radiation that is seen in large parts of Kerala and its possible linkage to cancer. 

K S Parthasarathy, former secretary of the Atomic Energy Regulatory Board and a specialist on radiation biology, reports that “parts of Kerala and Tamil Nadu are high background radiation areas (HBRA) because of the presence of large quantities of monazite in the soil. Thorium content in monazite ranges from 8-10.5 per cent.” 

“Researchers found that the radiation levels in 12 panchayats in Karunagappally varied between 0.32 and 76 milli-grays per year; the levels in 90 per cent of over 71,000 houses were more than one milli-gray per year. The average value of population dose in HBRA is 3.8 milli-gray per year. One milli-gray is the average value for areas of normal background radiation.”

In the upcoming issue of the Journal of the Endocrine Society, researchers Indu Elizabeth Mathew and Aju Mathew from the University of Kentucky, US, report on “Rising thyroid cancer incidence in southern India, an epidemic of over diagnosis?” 

The Mathews say, “Thyroid cancer is particularly prone to the phenomenon of over-diagnosis, whereby large numbers of sub-clinical case are diagnosed without a positive impact on thyroid cancer-specific mortality.” 

While the Kerala thyroid cancer cohort shows a large increase but when compared to similar samples from Delhi, Mumbai, Bengaluru and Chennai where no large jumps were seen thyroid cancer cases, makes the Mathews suggest that the Kerala increase may really be a case of ‘over-diagnosis’. They find that “women in Kerala less than 40 years of age are at high risk for increased diagnosis of thyroid cancer, over diagnosis impacts younger women more than the elderly.”