Thyroid Cancer and Gender-Affirming Hormone Therapy: Exploring a Potential Link

Although it’s a relatively uncommon form of cancer, thyroid cancer is among the most prevalent of endocrine malignancies. In fact, according to the American Cancer Society, thyroid cancer is three times more prevalent in women than in men.

However, investigators from UC Davis and the VA in Northern California unveiled a new aspect of thyroid cancer prevalence as transgender women (individuals assigned male at birth but identifying and living as female), specifically veterans, might be at an increased risk.

And while there are notable limitations to the study including a small sample size, it does beg the question: is there a link between the use of gender-affirming hormone therapy (GAHT) and thyroid cancer?

Before we dive into this interesting research, let’s review what we know.

• The thyroid: a gland which produces hormones that have roles in regulating metabolism, growth, body temperature, heart rate, and blood pressure. Thyroid cancer typically does not affect thyroid function.
• Thyroid Cancer:
  • Types: papillary, follicular, medullary, and anaplastic, with the most prevalent being papillary thyroid cancer, which appears in approximately 80 percent of cases.
  • Risk factors: radiation exposure, family history, and certain genetic syndromes, although the exact causes of thyroid cancer are not fully understood.
• GAHT: as a cornerstone of care for transgender individuals, this approach often uses hormones testosterone or estrogen to align secondary sex characteristics consistent with one’s gender identity.

Potential Intersection of Thyroid Cancer and GAHT

Estrogen, a hormone predominantly found in females, has been implicated in promoting the growth of certain types of cancer cells, including those in the thyroid gland. GAHT for transgender women typically includes estrogen medication. Estrogen receptors are present in some thyroid cancers, and some researchers hypothesize that estrogen therapy might play a role in their development or growth.

A study published in the Journal of the Endocrine Society examined the prevalence of thyroid cancer among transgender female veterans in the United States. In a retrospective analysis, nearly 9 million electronic heath records within the VA system were evaluated. The prevalence of thyroid cancer rates of transgender women who met inclusion criteria were compared to cisgender (individuals whose gender identity aligns with their sex assigned at birth) male and female veterans.

In terms of the results, the study revealed a prevalence of 0.341 percent for thyroid cancer among transgender female veterans, falling between the prevalence observed in cisgender men (0.187 percent) and cisgender women (estimated at 0.641 percent). While higher than the rate in men, it's important to note that it's not as high as the rate in women assigned female at birth. And although the evidence is not conclusive, it raises important questions about the long-term effects of GAHT on thyroid health and cancer risk.

The Road Ahead

While further research is necessary to gain a deeper understanding, insights from this study suggest the potential link between GAHT and thyroid cancer risk in transgender women. Longitudinal studies and larger sample sizes will be crucial for establishing a clearer cause-and-effect relationship, if any.

Nonetheless, thyroid cancer is a concern for all individuals, and transgender female veterans might be at a slightly higher risk compared to cisgender men; however, the absolute risk remains low. But there’s a strong argument, and perhaps a shift in behavior by healthcare professionals, towards a screening model focused on the physical anatomy the patient has rather than solely sex or gender. This approach may be one of the many steps to take to provide individualized care to promote early detection and improve health outcomes.

References

American Cancer Society. Cancer Facts & Figures 2024. Atlanta: American Cancer Society; 2024.

Cedars-Sinai. Gender Affirming Cancer Screening. Updated June 13, 2022. Accessed May 9, 2024. https://www.cedars-sinai.org/blog/gender-affirming-care.html#:~:text=Transgender%20women%20who%20have%20undergone,lower%20than%20non%2Dtransgender%20women.

Christensen JD, Basheer HT, Lado Abeal JJ. Thyroid Cancer Prevalence, Risk Exposure, and Clinical Features Among Transgender Female Veterans. J Endocr Soc. 2024;8(6):bvae060. Published 2024 Mar 27. doi:10.1210/jendso/bvae060

National Cancer Institute. SEER Cancer Stat Facts: Thyroid Cancer. Updated April 17, 2024. Accessed May 9, 2024. https://seer.cancer.gov/statfacts/html/thyro.html