Increasing cases of thyroid cancer in Kerala keeping doctors on their toes; no explanation yet

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New Delhi: Doctors in Kerala are at unease due to the gradually growing number of thyroid cancer cases in the state.

With no explanation behind the sudden upsurge, many factors are being considered. 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?

Some anti-nuclear activists have suggested that the neighbouring Kudankulam nuclear power plant could also be a possible cause, since thyroid cancers are usually linked to exposure to radiation.

Scientists are of the opinion that since Kerala has some of the finest healthcare facilities in India, this could merely be a case of over-diagnosis.

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."

The report by the Mathews states that "the phenomenon of over diagnosis seems to be the most plausible explanation for the significant burden of thyroid cancers in Kerala. It is not without significant personal and societal costs... It could result in over treatment, which profoundly increases risks for heart diseases, strokes and osteoporosis."

A similar case of over diagnosis of thyroid cancers was encountered a few years ago in South Korea, where according to a 2015 report in the New England Journal of Medicine between 2011 and 2014 there was a 15 times higher rate of thyroid cancer cases.

This was also traced to be a case of over diagnosis. But once this was highlighted by the medical fraternity there seems to have been a reversal.

The linkage to high-background radiation and cancers wasalso discounted and according to Parthasarathy, "a study at the HBRA during 1990-1999 by the researchers from the Regional Cancer Centre and Bhabha Atomic Research Centre did not show any health effect attributable to radiation."

Aju Mathew adds: "The linkage to high background radiation is unclear and unlikely. If it is indeed the case, then more cases of advanced thyroid cancer would occur. And there would be a commensurate rise in mortality rate which is at present comparable to other cities in India."

So is this over diagnosis of thyroid cancers in Kerala harming the patients?

Aju Mathew says, "Yes, absolutely. Over diagnosed cases are those that would not have caused a problem for the patient ever. All those patients undergo extensive surgery, some get radioactive iodine treatment, and all are placed on high dose thyroid medications."

The study has its limitations as it is based on limited data yet the Mathews give an ominous warning: "If the rise in thyroid cancer is not curtailed, it will lead to significant burden on the health and economic welfare of the people of Kerala."

Since Aju Mathew says, "Nearly 80 per cent cases can be attributed to over diagnosis."

(With PTI inputs)