The incidence (i.e. the number of new cases) of thyroid cancer has seen an increase in the past few decades. However, during the same period of time, there has also been an increase in the utilisation of imaging and biopsy to help detect thyroid cancer. As a result, the increased incidence of thyroid cancer in the recent past may not actually be due to a true increase in the number of cases of thyroid cancer. Rather, that more cases of thyroid cancer are being detected with the increased use of ultrasound and fine needle aspiration.
Increased Use of Thyroid Ultrasound and Fine Needle Aspiration Biopsy
The study by Zevallos et al., aimed to determine if the increased thyroid cancer incidence observed corresponded with a similar increase in the use of diagnostic investigations. Thyroid ultrasound and fine needle aspiration. This was achieved by examining the Veteran’s Affairs health system records. The number of cases of thyroid cancer and the numbers of diagnostic investigations performed in the period between the years 2000 and 2012 were compared. At the commencement of the study in 2000, the incidence of thyroid cancer was 10.3 cases per 100,000 people. In comparison, at the study’s conclusion in 2012, the incidence of thyroid cancer was 21.5 cases per 100,000 people.
As with the incidence of thyroid cancer during the study period, the use of ultrasound and fine needle aspiration biopsy also exhibited an increase. In 2000, the rate of thyroid ultrasound was 125.6 per 100,000 people, which had increased to 572.1 per 100,000 people in 2012. Similarly, in 2000 the rate of fine needle aspiration biopsy was 7 per 100,000 people, but rose to 46.2 per 100,000 by 2012.
What this result really means is that due to better access to testing for thyroid cancer, the number of cases that are detected increases. This does not necessarily mean that thyroid cancer is becoming more common. Rather, we are becoming better at detecting it. This finding is also likely to be because patients with small thyroid nodules are being over-investigated. The American Thyroid Association (ATA) recommends that all patients with a thyroid nodule should have their thyroid stimulating hormone level tested. If this comes back with a low result, they recommend that the patient has a radionuclide thyroid scan. Additionally, the ATA also recommends that all patients with suspected or known thyroid nodules have an ultrasound assessment of the thyroid, and endorse that fine needle aspiration is the investigation of choice for a thyroid nodule.
Zevallos JP., et al. (2015). Increased thyroid cancer incidence corresponds to increased use of thyroid ultrasound and fine-needle aspiration: A study of the Veterans Affairs health care system. Cancer, 121(5), 741-746. http://www.ncbi.nlm.nih.gov/pubmed/25376872