Thyroid Cancers, Incidence-Based Mortality Rising in California

By Anne Harding

March 25, 2020

NEW YORK (Reuters Health) - Thyroid-cancer incidence and incidence-based mortality have been increasing in California since 2000, a new study shows.

"This may be, in part, due to more sensitive screening and earlier detection of smaller tumors," Dr. Angela M. Leung of UCLA David Geffen School of Medicine and the VA Greater Los Angeles Health System told Reuters Health by email. "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."

U.S. thyroid-cancer incidence is going up by about 3.6% annually, largely due to increases in papillary thyroid cancers (PTCs), Dr. Leung and her team note in the Journal of Clinical Endocrinology and Metabolism.

"Despite general acknowledgement that thyroid cancer overdiagnosis . . . is occurring worldwide, the fact that large thyroid cancers are found more frequently today suggests that overdiagnosis alone may not fully explain the observed trends," they add.

To investigate statewide trends, the authors looked at 2000-2017 data from the California Cancer Registry (CCR) on close to 70,000 people with thyroid cancer, 2,562 of whom died from the disease during the study period. PTCs accounted for 87.8% of cases, 7.2% follicular and 1.8% medullary. Three-quarters of deaths were in patients over 60.

Thyroid-cancer incidence rose from 6.43 to 11.13 per 100,000 person-years during the study period, they found, increasing by 4% per year, on average, and peaking in 2015 at 12.73 per 100,000 person-years.

Women represented 76% of patients, and their thyroid-cancer incidence was 15.42 per 100,000 person years. Men's incidence was 4.68 per 100,000 person years.

Trends were similar for women and men and for all races and ethnicities. Incidence of PTC, medullary and anaplastic histological thyroid-cancers increased, while follicular-carcinoma incidence was unchanged. Incidence of localized and regional cancers increased, while distant-cancer incidence fell.

Incidence increased for tumors of all sizes, with the biggest rise seen for tumors of at least 2 cm.

Incidence-based mortality for thyroid cancer rose 1.7% per year. PTC mortality increased by 2.3% annually and anaplastic thyroid cancers by 3.5% annually, while mortality was stable for follicular thyroid cancer and declined 3.8% annually for medullary thyroid cancer.

Men's thyroid-cancer mortality increased by 2.7% annually, and mortality rates also increased for regional stage PTCs but not for localized or distant disease. Mortality rates increased by 5.1% annually for tumors 1-2 cm, 3.4% for tumors 2-4 cm and 2.6% for tumors larger than 4 cm.

Women's thyroid-cancer mortality was unchanged, and mortality rates were also stable for patients with tumors of 1 cm or smaller.

"The rise in thyroid cancer can potentially be explained by a complex interplay of environmental, dietary and/or genetic factors," Kimberly Yan of UCLA David Geffen School of Medicine, first author of the study, told Reuters Health by email. "Some plausible contributors include greater cumulative ionizing radiation exposure associated with increased medical and dental imaging, exposure to nitrates and other environmental toxicants, and an increase in iodine intake."

Yan and Dr. Leung noted that the CCR could also be used to investigate how thyroid-cancer incidence is associated with geographic location, to help determine the role of environmental exposures and other potential risk factors.

SOURCE: Journal of Clinical Endocrinology and Metabolism, online March 13, 2020.


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