Thyroid cancer and ovarian cancer share several biological connections, from genetics and hormonal pathways to a rare condition where thyroid tissue actually grows inside the ovary. These links don’t mean one cancer causes the other, but they do explain why the two show up together more often than you might expect.
The Estrogen Connection
Both thyroid and ovarian cancers are influenced by estrogen, which helps explain why thyroid cancer is roughly three times more common in women than in men. Estrogen promotes the growth and invasion of mutated thyroid cells, and it does so through a specific receptor called estrogen receptor alpha (ER-alpha). This same receptor drives cell growth in ovarian cancer. In both cancer types, ER-alpha has a proliferative effect, encouraging cells to multiply and resist normal cell death, while a second receptor (ER-beta) works in the opposite direction, slowing growth and promoting cell differentiation. The balance between these two receptors appears to determine how aggressively estrogen fuels tumor growth in both organs.
Estrogen also enhances the ability of both thyroid and ovarian cancer cells to spread. In papillary thyroid cancer cells, estrogen increases adhesion, migration, and invasion. In ovarian cancer cells, it boosts enzymes that break down surrounding tissue while reducing molecules that hold cells in place. This parallel behavior suggests a shared hormonal vulnerability.
TSH Receptors in Ovarian Tissue
One of the more surprising findings is that ovarian tissue carries receptors for thyroid-stimulating hormone (TSH), the same receptors found on thyroid cells. Researchers at the Chinese University of Hong Kong discovered that TSH receptors exist in both normal ovarian surface tissue and in human ovarian cancers. When they activated these receptors in lab-grown ovarian cancer cells, the cells proliferated at a rate comparable to what gonadotropins (the hormones that normally stimulate the ovaries) produce. Blocking the receptor slowed cancer cell growth in long-term cultures.
This means a signaling system that evolved long before the reproductive hormone system can, under certain conditions, drive ovarian cancer cell growth through the same pathways thyroid cells use. The discovery doesn’t prove that thyroid dysfunction causes ovarian cancer, but it reveals a biological bridge between the two organs that researchers are still working to fully understand.
A Shared Genetic Risk: PTEN Mutations
A specific genetic mutation ties the two cancers together more directly. Mutations in the PTEN gene, a tumor suppressor that normally keeps cell growth in check, are associated with a nearly fivefold increased risk of thyroid cancer (odds ratio of 4.88) and close to a fourfold increased risk of ovarian cancer (odds ratio of 3.77). These findings come from a large study of over 727,000 people who underwent multigene panel testing.
PTEN mutations are the hallmark of Cowden syndrome, a hereditary condition that raises the risk of multiple cancers. About 11% of people with Cowden syndrome develop thyroid cancer as their first cancer diagnosis. Not everyone with a PTEN mutation meets the clinical criteria for Cowden syndrome, but all carriers face elevated cancer risks across several organs, including both the thyroid and the ovaries. PTEN mutations are found in roughly 30 to 35% of people clinically diagnosed with Cowden syndrome and about 60% of those with the related condition Bannayan-Riley-Ruvalcaba syndrome.
When Thyroid Tissue Grows in the Ovary
The most literal connection between the two cancers is a condition called struma ovarii, where functioning thyroid tissue develops inside an ovarian tumor. About 20% of ovarian germ cell tumors contain some thyroid tissue, though only 5% contain enough (more than half the tumor) to qualify as struma ovarii. In rare cases, this thyroid tissue becomes cancerous. Thyroid carcinoma arising from struma ovarii accounts for roughly 0.01% of all ovarian cancers and 5 to 10% of all struma ovarii cases.
Some patients are diagnosed with cancerous struma ovarii and a separate primary thyroid cancer in the neck at the same time. A literature review of 13 such synchronous cases found that no patients died of disease, with 11 showing no evidence of disease after a median follow-up of two years. More broadly, patients with malignant struma ovarii have strong survival outcomes: five-year overall survival is around 96.7%, and even patients with metastatic disease have five-year survival rates near 89%. The coexistence of thyroid cancer in the neck does not appear to worsen outcomes.
Endocrine Disruptors Affect Both Organs
Environmental chemicals that interfere with hormone signaling, known as endocrine disruptors, have been linked to increased cancer risk in both the thyroid and the ovaries. A forty-year systematic review found that the thyroid had the highest cancer risk of any organ after exposure to endocrine disruptors, with 67% of studies showing a positive association. The ovary showed the lowest association among endocrine-related cancers, at 43%, but this still represents a meaningful signal. The chemical groups most strongly tied to cancer across both organs include phthalates (found in plastics and personal care products), heavy metals, particulate matter from air pollution, and pesticides.
These chemicals can mimic or block estrogen and thyroid hormones, potentially amplifying the hormonal pathways that both cancers already exploit. The fact that endocrine disruptors disproportionately affect the thyroid, where cancer incidence has been rising for decades, and also show a measurable effect on the ovary reinforces the idea that these two organs share hormonal vulnerabilities.
What This Means for Screening
Despite these biological connections, no major clinical guidelines currently recommend routine ovarian cancer screening for women with a history of thyroid cancer. This isn’t because the link is unimportant. It’s because the available screening tools for ovarian cancer, including transvaginal ultrasound and the CA-125 blood test, have not been shown to reduce deaths from the disease, even in high-risk populations.
The exception is genetic. If you carry a PTEN mutation or have been diagnosed with Cowden syndrome, your healthcare team will typically recommend a more comprehensive cancer surveillance plan that covers multiple organs. For the broader population of thyroid cancer survivors, the shared biology is worth being aware of, but it doesn’t yet translate into specific screening recommendations beyond what’s standard for your age and risk factors.