Study of thyroid cancer in Italy points to better surveillance, not higher incidence
A survey of 15 years' worth of data mined from Italy's cancer registries has found that though diagnoses of the disease have increased over time, this surge appears to be due mainly to improvements in medical surveillance and tumor detection.
A report published in the journal Annals of Oncology
found that most of the increase in reported thyroid carcinoma cases was due to papillary thyroid cancer (PTC), the only form of the disease that appeared with substantially greater frequency during the survey period.
Among all Italians under the age of 85, the incidence of all types of thyroid cancer approximately doubled between the study's first and last five-year segments.
Between 1991 and 1995, an average of 8.2 women per 100,000 were diagnosed with a thyroid carcinoma, a figure that rose to 17.6 women per 100,000 between the years of 2001 and 2005. Likewise, the incidence of thyroid tumors increased among Italian men from 3.1 cases per 100,000 to 5.7 cases per 100,000.
Overall, approximately 10,700 diagnoses of thyroid cancer were reported among women, and nearly 3,400 cases among men.
However, while these statistics may seem grim, the study's authors made a number of statistical discoveries suggesting that the apparent shift in Italian thyroid cancer rates was primarily one of measurement, not of the disease's actual prevalence.
For one thing, virtually all of the additional thyroid carcinoma cases were attributable to diagnoses of PTC. The incidence of PTC increased by 145 percent among women and 127 percent among men over the study's data period.
While medullary thyroid cancer saw a moderate increase in prevalence, overall the non-papillary varieties of the disease did not experience nearly the statistical growth that PTC did.
What does this disparity mean? The team noted that a strong statistical period effect indicated that the overall increase in thyroid cancer was due to better and more widely available medical surveillance.
They also noted that the use of in-hospital radiological exams has doubled in the past decade and a half in the U.S. and, in all likelihood, in Italy. More sensitive tumor detection aside, the use of medical radiation might account for a small fraction of any actual increase in thyroid cancer rates, since repeated radiological scans of the head and neck can increase the risk of genetic damage in thyroid cells.
The team added that the increase in the sensitivity of medical exams may account for the jump in PTC rates, since many cases of the often asymptomatic variety of thyroid cancer used to go unnoticed until autopsy.
Italy has one of the highest rates of thyroid cancer diagnoses in the world, the International Agency for Research on Cancer reports. The country's Associazione Italiana Registri Tumori found that thyroid tumors are the second most common cancer among Italian women and the fifth most prevalent among men.
In the U.S., 16.3 women per 100,000 and 5.6 men per 100,000 are diagnosed with thyroid cancer each year, according to the National Cancer Institute.