The epidemiology of the increased incidence of thyroid cancer, which has nearly tripled since 1975, “suggests that it is not an epidemic of disease but rather an epidemic of diagnosis,” Louise Davies, MD, MS, and H. Gilbert Welch, MD, MPH, concluded after analyzing trends in patients diagnosed with thyroid cancer between 1975 and 2009.
“Our findings demonstrate that the problem is due to the overdiagnosis of papillary thyroid cancer, an abnormality often present in people who never develop symptoms from it,” Drs. Davies and Welch wrote. “We also found that the major burden of overdiagnosis has fallen on women.” Women now have higher cancer detection rates by a 3:1 ratio.
“Over the past 35 years the absolute increase in thyroid cancer in women was almost 4 times greater than that in men. This is particularly notable because thyroid cancer prevalence at autopsy is actually greater in men than it is in women. This suggests that the problem of overdiagnosis of thyroid cancer in women has probably been present for decades,” the authors stated.
Their study used data from men and women aged 18 and older diagnosed with cancer in nine geographic areas within the Surveillance, Epidemiology, and End Results (SEER) program, as well as thyroid cancer mortality from the National Vital Statistics System. Because thyroid cancer is “commonly found in people who have died of other causes, and because thyroid cancer mortality had been stable,” Dr. Davies and Dr. Welch had argued when previously reporting a doubling of thyroid cancer incidence that “the increased incidence represented overdiagnosis.”
The most recent data from 2008 and 2009 showed that 39% of thyroid cancers detected were 1 cm or smaller, while tumors larger 2 cm represented a smaller portion, 33% vs 42% in 1988 to 1989. More than 90% of those diagnosed have surgery, and about 50% of those patients also receive radiation therapy. “Many also undergo a lymph node dissection,” the researchers reported.
Drs. Welch and Davies are on staff at the Veterans Affairs Medical Center in White River Junction, Vermont. Dr. Welch, who is also Professor of Medicine at the Dartmouth Institute for Health Policy and Clinical Practice in Hanover, New Hampshire, recently coauthored a study—“Quantifying the benefits and harms of screening mammography” (JAMA Intern Med, December 30, 2013, early release online)—that raised the issue of overdiagnosis of breast cancer, and wrote a related op-ed piece about that study for The New York Times. (Dr. Welch discussed that study during an interview published in the February 15 issue of The ASCO Post.) He is also coauthor of a book entitled, Overdiagnosed: Making People Sick in the Pursuit of Health.
Incidence Has Tripled
“Since 1975, the incidence of thyroid cancer has now nearly tripled, from 4.9 to 14.3 per 100,000 individuals [absolute increase = 9.4 per 100,000; relative rate (RR) = 2.9; 95% CI = 2.7–3.1]. Virtually the entire increase was attributable to papillary thyroid cancer: from 3.4 to 12.5 per 100,000 [absolute increase = 9.1 per 100,000; RR = 3.7; 95% CI = 3.4–4.0],” according to the current analysis. “The absolute increase in thyroid cancer in women [from 6.5 to 21.4 = 14.9 per 100,000 women] was almost 4 times greater than that of men [from 3.1 to 6.9 = 3.8 per 100,000 men]. The mortality rate from thyroid cancer was stable between 1975 and 2009 [approximately 0.5 deaths per 100,000].”
Dr. Davies and Dr. Welch proposed several methods to address 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,” they stated. “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,” they noted.
Another approach would be to reclassify incidentally identified small thyroid neoplasms “using a term other than cancer.” In the meantime, physicians could “openly share with patients the uncertainty surrounding small thyroid cancers—explaining that many will never grow and cause harm to a patient—but it is not possible to know with certainty which ones fall into that category,” the authors advised.
“Physicians’ thresholds to palpate, image, and biopsy the thyroid have likely fallen too far,” Drs. Davies and Welch added. “Clinicians need more than trial results; they also need to be asking themselves whether they are looking too hard for thyroid cancer. Patients—and in the case of thyroid cancer, particularly women—need protection not only from the harms of unnecessary treatment but also the harms of unnecessary diagnosis.” ■
Davies L, Welch HG: JAMA Otolaryngol Head Neck Surg. February 20, 2014 (early release online).