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Subclinical diagnoses may skew thyroid cancer survival data
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Improved thyroid cancer survival rates may be misleading due to the growing number of asymptomatic cancers diagnosed through improved detection methods, according to study results.
Treatment decisions based on these improved survival data may reinforce inappropriately aggressive management, researchers wrote.
“Over the past 3 decades, thyroid cancer incidence has increased dramatically, but the natural history of the disease has not necessarily changed, a phenomenon that has been called an epidemic in diagnosis rather than an epidemic in disease,” Allen S. Ho, MD, of the department of surgery at Memorial Sloan Kettering Cancer Center, and colleagues wrote. “We hypothesized that the increasing diagnosis of subclinical thyroid cancers has led to an increasing proportion of small, localized tumors, and that this shift is associated with the appearance of improving thyroid cancer survival.”
Researchers analyzed changes in presentation and survival statistics in thyroid cancer from patients treated at Memorial Sloan Kettering from 1950 to 2005 and from SEER cancer registry data from 1973 to 2009.
Overall, U.S. age-adjusted thyroid cancer incidence increased from 4.9 cases to 14.8 cases per 100,000 persons between 1975 and 2009. Researchers noted this increase is primarily attributable to the 3.7-fold increase in papillary thyroid cancer (3.4 to 12.5 per 100,000 persons).
However, during this time period, the mortality rate remained unchanged (annual percentage change, –0.2%; 95% CI, –0.7 to 0.2).
The proportion of newly diagnosed thyroid cancers measuring 1 cm or smaller increased from 23% in 1983 to 36% in 2009. At Memorial Sloan Kettering, incidence of subcentimeter thyroid cancers also increased from 20.3% in 1950 to 34.6% in 2005.
However, from 1983 to 2009, significant declines occurred in the incidence of tumors larger than 6 cm (4% vs. 2%; P ˂ .001) and the proportion of patients presenting with distant metastases (3.7% vs. 3.1%; P = .01).
SEER data demonstrated that 10-year relative survival in patients diagnosed with thyroid cancer between 1983 and 1999 has increased from 95.4% to 98.6% (P = .002). In the Memorial Sloan Kettering setting, 10-year disease-specific survival for patients diagnosed between 1950 and 2005 also increased from 91.1% to 96.1%.
Researchers observed no significant changes in survival outcomes when they stratified data by tumor size (≤ 1 cm, 1.1-3.9 cm, and ≥ 4 cm) and stage.
“Modern medical practices increasingly uncover small, asymptomatic thyroid cancers,” Ho and colleagues wrote. “Survival rates appear improved, but this finding is spurious, attributable instead to shifts in the characteristics of disease being diagnosed. Relying on survival rates to measure success in treating thyroid cancer may reinforce inappropriately aggressive management. Treatment decisions in thyroid cancer should be made based on mortality, not survival data.” – by Lauren Frisby
Disclosure: The researchers report no relevant financial disclosures.
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