Incidence and gender difference of brain metastases in newly diagnosed follicular thyroid cancer patients.

Background: Population-based estimates of brain metastases in follicular thyroid cancer (FTC) patients with or without distant metastases (DMs) at diagnosis are lacking.

Objective: To study the prevalence of brain metastases in FTC patients and compare gender disparity.

Methods: DMs are defined as bone, lung, and brain metastases. Using the SEER database, we identified 5116 patients diagnosed with FTC between 2010 and 2019. The incidences of brain metastases were calculated for the entire cohort and among patients with bone/lung metastases. Cohorts were stratified by gender and age.

Results: 4.8% (245) had DMs at diagnosis, primarily in the form of bone metastases (3.6%), followed by lung metastases (2.4%). The incidence of brain metastases at initial diagnosis was only 0.37% (17 females and 2 males), but occurred in 8.2% and 6.1% of patients with bone metastases and lung metastases, respectively. Median survival for patients with brain metastases was only 8.0 months (95% CI, 4.1-11.9). Interestingly, female patients with bone metastases exhibited a significantly higher incidence of brain metastases compared to males (12.0% vs. 1.5%), with a notable odds ratio of 8.971 (95% CI:1.152-69.835) in univariate analysis. Multivariate logistic regression analysis confirmed that being female (odds ratio, 10.08; 95% CI:1.243-81.748) was the sole statistically significant risk factor for brain metastases in FTC patients with bone metastases at diagnosis.

Conclusion: An incidence of brain metastases is observed in newly diagnosed FTC patients with DMs, especially in females with bone involvement. Our findings advocate for the early detection of brain metastases in female FTC patients with concurrent bone metastases at diagnosis.