In a study reported in JAMA Otolaryngology Head & Neck Surgery,1 Davies and Welch found that the incidence of thyroid cancer has nearly tripled since 1975. However, the increase appears to represent an “epidemic of diagnosis” and to almost exclusively represent increased diagnosis of papillary thyroid cancer. The investigators had previously reported a doubling of thyroid cancer incidence largely due to detection of small papillary cancers. Since these are commonly found in people who have died of other causes and since thyroid cancer mortality had been stable, the investigators had hypothesized that the increased incidence represented overdiagnosis.
The current study involved analysis of thyroid cancer incidence, histologic type, tumor size, and mortality using data from 1975 to 2009 from nine Surveillance, Epidemiology, and End Results (SEER) areas (Atlanta, Connecticut, Detroit, Hawaii, Iowa, New Mexico, San Francisco-Oakland, Seattle-Puget Sound, and Utah) and data on thyroid cancer mortality from the National Vital Statistics System.
Tripled Incidence
Since 1975, the incidence of thyroid cancer in men and women aged ≥ 18 years has nearly tripled, from 4.9 to 14.3/100,000 individuals (absolute increase = 9.4 per 100,000, relative rate [RR] = 2.9). More than half this increase (5.1/100,000) occurred during the 7 years since the investigators’ last study. Nearly all of the increase is attributable to a 9.1/100,000 increase in incidence of papillary thyroid cancer (from 3.4 to 12.5/100,000, RR = 3.7). The increase in thyroid cancer in women (14.9/100,000, from 6.5 to 21.4/100,000, RR = 3.3) was nearly 4 times greater than that in men (3.8/100,000, from 3.1 to 6.9/100,000, RR = 2.2).
Diagnosed tumors have gotten smaller. The proportion of tumors ≤ 1 cm has increased from 25% in 1988 to 1989 to 39% in 2008 to 2009. Over the same period, the proportion > 2 cm has decreased from 42% to 33%.
Treatments and Mortality
Among the approximately 56,000 Americans diagnosed with thyroid cancer who were treated in 2009, median age at diagnosis was 49 years for women and 53 years for men. More than 90% of both women and men underwent surgery, with approximately half of these patients undergoing radiation therapy, and 50% and 56% had lymph node dissection.
The mortality rate from thyroid cancer was stable between 1975 and 2009, at approximately 0.5 deaths per 100,000 population.
The investigators concluded, “There is an ongoing epidemic of thyroid cancer in the United States. The epidemiology of the increased incidence, however, suggests that it is not an epidemic of disease but rather an epidemic of diagnosis. The problem is particularly acute for women, who have lower autopsy prevalence of thyroid cancer than men but higher cancer detection rates by a 3:1 ratio.”
They further stated, “We believe the time has come to address the problem of papillary thyroid cancer overdiagnosis and overtreatment. Providing patients with randomized clinical trial data on an alternative approach—active surveillance of incidentally identified, asymptomatic, small papillary thyroid cancers—is the logical next step. We are pleased to see effort in this direction, both in Japan, where patients have been followed for up to 10 years with favorable results, and in the United States, where Memorial Sloan-Kettering Cancer Center is successfully recruiting patients into an observational cohort.” ■
Disclosure: The study was supported by the Department of Veterans Affairs and The Dartmouth Institute for Health Policy and Clinical Practice. The study authors reported no potential conflicts of interest.
Reference
1. Davies L, Welch G: Current thyroid cancer trends in the United States. JAMA Otolaryngol Head Neck Surg 140(4):317-322, 2014.
