'Consistent increase' observed in larger, more aggressive thyroid tumors in California
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A retrospective analysis of diagnosed thyroid cancer cases in California revealed a consistent increase in the diagnosis of larger and more aggressive thyroid tumors that correlated with a rise in incidence-based mortality among men and individuals with tumors larger than 1 cm, according to findings published in The Journal of Clinical Endocrinology & Metabolism.
“Our findings show that over the past few decades, the number of newly diagnosed thyroid cancers in California has risen,” Angela M. Leung, MD, MSc, associate professor of medicine in the division of endocrinology, diabetes and metabolism of the department of medicine of the David Geffen School of Medicine at UCLA, told Healio. “This may be, in part, due to more sensitive screening and earlier detection of smaller tumors. However, the concurrent rise in the incidence and incidence-based mortality of larger and more aggressive tumors may indicate a true biological rise in thyroid cancer.”
In a retrospective analysis, Leung and colleagues analyzed data from 69,684 adults diagnosed with thyroid cancer between 2000 and 2017 (76.3% women; 78.2% white; median age at diagnosis, 50 years), using data from the California Cancer Registry, a mandatory cancer reporting system capturing all health care institutions in California. Researchers assessed overall incidence and incidence-based mortality during the study period, with annual incidences calculated as the number of thyroid cancers diagnoses across the total annual California population (using U.S. Census Bureau statistics). They used stratified logistic regression analyses to estimate annual percent change in age-adjusted incidence and incidence-based mortality.
During the study period, researchers observed 2,562 thyroid cancer-specific deaths.
Researchers found that overall incidence of thyroid cancer increased across all histological subtypes during the study period — papillary, follicular, medullary and anaplastic — and across all tumor sizes.
Overall thyroid cancer incidence ranged from 6.43 to 11.13 per 100,000 person-years, with an increase of 10.06 diagnoses (95% CI, 9.99-10.14) per 100,000 person-years between 2000 and 2017. Researchers found that incidence rates increased by an average of 4% per year (P < .001), with no significant between-sex or between-race differences.
“Papillary, medullary and anaplastic histological subtypes showed increasing incidence rates, while the incidence of follicular carcinoma remained stable,” the researchers wrote.
Thyroid cancer-specific mortality rates increased on average by 1.7% per year (P < .001). The increased mortality rates were greater among men (2.7% per year; P < .001) and among individuals with tumors between 2 cm and 4 cm (3.4% per year; P < .05).
“Though men accounted for 23.7% of new thyroid cancer cases, they accounted for 40.6% of thyroid cancer deaths,” the researchers wrote.
The researchers noted a “consistent increase” in disease incidence at all papillary thyroid carcinoma sizes, including tumors at least 4 cm in size, which would be “difficult to attribute to radiographic discovery alone.”
“Our study was conducted using the California Cancer Registry, which is unique in its depth and comprehensively linked data containing demographics, diagnostic, treatment and outcome for all cancer diagnoses in the state,” Kimberly Lim Yan, BS, a doctoral candidate at the David Geffen School of Medicine at UCLA, told Healio. “With this resource, additional studies could potentially address the associations of thyroid cancer based on geographical location, in order to assess the contributions of environmental exposures and other potential risk factors.” – by Regina Schaffer
For more information:
Angela M. Leung, MD, MSc, can be reached at amleung@mednet.ucla.edu.
Disclosures: The authors report no relevant financial disclosures.
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Cari Kitahara, PhD
This California cancer registry-based study follows our earlier study in JAMA that used data from the SEER-9 cancer registries in the United States, with some degree of overlap between the two study populations (Lim H, et al. JAMA. 2017; doi:10.101/jama.2017.2719). Like the authors of the current study, we previously found increasing incidence rates and thyroid cancer mortality rates among patients diagnosed with larger and more advanced papillary thyroid carcinomas. It is possible that environmental or lifestyle-related risk factors may have contributed to these trends. Obesity, for example, has been consistently associated with risk for thyroid cancer in observational studies, and like papillary thyroid carcinoma, the prevalence of obesity has increased substantially in the United States. We previously estimated that obesity may account for about 15% of the overall increase in papillary thyroid carcinoma (Kitahara CM, et al J Natl Cancer Inst. 2019; doi:10.1093/jnci/djz202). More research is needed to identify modifiable risk factors for this disease and to understand how we can prevent thyroid cancer from developing in the first place.
While increases in incidence of aggressive thyroid cancers and thyroid cancer mortality are concerning, thyroid cancer overdiagnosis has been a tremendous — and growing — public health issue in the United States and worldwide since the 1980s, and has contributed to a much larger absolute increase in the number of thyroid cancer cases over time. Most thyroid cancers are very slow growing. Many of these cancers would have never caused problems for these patients if left undetected. In recent years, however, clinical guidelines have shifted toward a less aggressive and more discerning approach to low-risk thyroid nodules and cancer. These changes will hopefully contribute to a reduction in unnecessary harms associated with diagnosis and treatment.
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