Differences in thyroid cancer by sex are mostly confined to small papillary thyroid cancers, a new study published in JAMA Internal Medicine found. The incidence and mortality of more lethal types of thyroid cancer such as medullary thyroid carcinoma (MTC) are similar between sexes.
It is believed that thyroid cancer is more common in women than in men. However, according to the findings of the present study, this is an oversimplification.
To compare the rate of sex-specific thyroid cancer in the United States and the prevalence of subclinical thyroid cancer at autopsy, a team of researchers led by Louise Davies, MD, MS, analyzed data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program about the incidence and mortality of thyroid cancer by sex between 1975 and 2017. They also searched the literature for studies on the prevalence of subclinical thyroid cancer at autopsy in people of both sexes until May 31, 2021.
The results showed that in 2017, the majority (90%) of thyroid cancers diagnosed were papillary thyroid cancer. Between 2013 and 2017, the incidence of small papillary thyroid cancers was 4.39:1 in women vs men. However, as cancer lethality increased, this ratio approached 1:1.
Read more about MTC pathophysiology
According to the results of the meta-analysis, the pooled autopsy prevalences of papillary thyroid cancers were 14% in women and 11% in men.
The mortality rate of small localized papillary thyroid cancers between 1992 and 2015 was 0.003 per 100,000. It was 0.084 per 100,000 for all other papillary thyroid cancers and 0.19 per 100,000 for all other thyroid cancers including medullary thyroid cancer.
“As the relative lethality of the cancer increased, the detection ratio moved closer to 1:1, with medullary and anaplastic cancers diagnosed more equally between sexes or slightly more in men during some time periods,” the researchers wrote.
The fact that the ratio of detection by sex approaches 1:1 as the lethality of the cancer type increases could be explained by gender disparities in the utilization of health care and clinical thinking between men and women, according to the authors. They wrote, “[This] can harm both women, who are subject to overdetection, and men, who may be at risk of underdetection.”
LeClair K, Bell KJL, Furuya-Kanamori L, Doi SA, Francis DO, Davies L. Evaluation of gender inequity in thyroid cancer diagnosis: differences by sex in US thyroid cancer incidence compared with a meta-analysis of subclinical thyroid cancer rates at autopsy. JAMA Intern Med. Published online August 30, 2021. doi:10.1001/jamainternmed.2021.4804