Dr. Marla Shapiro: Thyroid cancer rates on the rise, but why?
Published Wednesday, August 28, 2013 6:56AM EDT Last Updated Wednesday, August 28, 2013 7:00AM EDT
Last year the Canadian Cancer Society published results that showed thyroid cancer incidence rates have been increasing substantially worldwide, but the reasons behind this increase are unclear.
In reviewing the existing evidence, the researchers found a positive association between BMI and an increased risk of thyroid cancer. The risk was higher for women than men, and among women the risk was up to 7 times greater in those with a high BMI compared to a lower BMI. A high BMI is an indication of overweight or obesity. The studies also noted that there are likely other factors, related to lifestyle or the environment, that together heighten the risk of thyroid cancer however they also pointed out that the big question we still need to answer is whether there is a true increase in risk or if we are simply getting better at detecting this type of cancer.
The authors cite a previous analysis of data from 5 continents that showed the average increase in thyroid cancer rates was 67 per cent in females and 48 per cent in males between 1973 and 2002. The increase in thyroid cancer incidence has been almost universal across countries.
Now a new study in the British Medical Journal questions whether it is as they call it-zealous imaging is fuelling unnecessary and harmful treatment of low risk thyroid cancers.
We are fortunate to have many new techniques with which to study suspect disease. This includes ultrasound, CT and MRI scanning which can detect thyroid nodules as small as 2 mm. While thyroid nodules are common, in fact most - more than 98 per cent - are actually benign. Making sure only nodules that have 2 or more worrisome features before biopsying, is thought to reduce unnecessary biopsies by 90 per cent while maintaining a low risk of cancer.
In the U.S., cases have tripled in the past 30 years - from 3.6 per 100,000 in 1973 to 11.6 per 100,000 in 2009 - making it one of the fastest growing diagnoses. Yet the death rate from papillary thyroid cancer has remained stable.
Researchers from the Mayo clinic argue that is this very expanding gap between incidence of thyroid cancer and deaths that suggests that low risk cancers are being overdiagnosed and overtreated.
The authors say that unnecessary thyroidectomy (the surgical removal of all or part of the thyroid gland) is costly and carries a risk of complications such as low calcium levels and nerve injury. In the U.S., the number of thyroidectomies for thyroid cancer has risen by 60 per cent over the past 10 years. Using radioactive iodine in patients with low risk thyroid cancer has also increased from one in 300 patients to two in five patients between 1973 and 2006, despite recommendations against using it, they add.
Many of these small lesions might have micropapillary thryoid cancer but many of them will not progress. While to goal is to reduce unnecessary imaging, when these small lesions are found the authors encourage physicians use a term that conveys favourable prognosis for low risk thyroid cancers (microPapillary Lesions of Indolent Course or microPLIC) and makes it easier to give patients the choice of active surveillance over immediate and often intensive treatment.