BACKGROUND
Thyroid ultrasound and biopsy have been used for evaluation of thyroid nodules since the 1970s. These methods improved detection and accurate diagnosis of thyroid cancer. At the same time pathology became more detailed and new technologies improved safety for thyroid surgeries. New cases of thyroid cancer more than tripled since 1990’s in many countries. There had been a question whether this was due to a true increase in cancer or whether we were detecting the cancer more often with better tools or both. Thyroid cancer has always been diagnosed more commonly in women than in men, this difference became more pronounced in recent years. However, a clear biologic reason was not found to explain the difference. This study was designed to understand how thyroid cancer risk varied by sex.

THE FULL ARTICLE TITLE
LeClair K et al 2021 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. Epub 2021 Aug 30. PMID: 34459841.

SUMMARY OF THE STUDY
The researchers used 2 large databases to collect information. Thyroid cancer incidence data from 1975 to 2017 were obtained from SEER (U.S. National Cancer Institute’s Surveillance, Epidemiology, and End Results Program-9 Registries). Data for yearly thyroid cancer mortality from 1975 to 2017 were obtained from NVSS (Center for Disease Control and Prevention’s National Vital Statistics System). They examined incidence trends (new cases per year) for thyroid cancer for women and men and performed a more detailed analyses by cancer type, stage and cancer size. The authors also identified autopsy studies that examined the entire thyroid gland and that reported the presence of small thyroid cancers that were unrelated to the cause of death and were only found at autopsy.

Thyroid cancer diagnoses started to increase in the 1990’s and peaked in 2013, mostly due to new diagnosis of papillary thyroid cancer. In the period of 1983 – 2017, the female-to-male ratio of all thyroid cancers was 2.75:1, while the female-to-male ratio of small (<2 cm), localized papillary thyroid cancer was 4.28:1. The ratios remained stable or decreased over time for all other papillary thyroid cancer sizes and for other types of thyroid cancer. As for the more lethal thyroid cancers (medullary and anaplastic), these were found equally in women and men. However, when all thyroid cancer types combined, women and men had an almost equal risk of death and this risk remained stable over time.

When they analyzed the data from autopsy studies that had reported small, incidentally found papillary thyroid cancer in patients who had died of other causes, they did not find any significant difference between women and men. (14% of women and 11% of men had papillary thyroid cancer only discovered at autopsy)

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The findings of this study do not support that women get thyroid cancer more often than men. Papillary thyroid cancer found at autopsy was similar between genders in autopsy studies. The difference between genders was due to detection of small papillary thyroid cancers more often in women. However, the increased detection in women was not associated with an improvement in survival, which is similar in both sexes.

These findings are very important for patients and their physicians. The ideal use of the advanced tools we have to evaluate thyroid abnormalities should be tailored to lead to early detection and treatment of clinically important cancers while avoiding overdetection and unnecessary treatment of clinically insignificant ones. The physicians should have a clear discussion with their patients about the risks, benefits, and extent of evaluation using the current guidelines.

—Ebru Sulanc, MD

Table of Contents | PDF File for Saving and Printing