Risk factors and outcomes of metastatic poorly differentiated thyroid carcinoma.

Background: Poorly differentiated thyroid carcinoma (PDTC) is a rare and aggressive form of thyroid cancer. Distant metastasis occurs frequently in PDTC.

Aim: To determine factors associated with distant metastasis and the effects of metastasis, either diagnosed on initial presentation or developing during follow-up, on mortality in PDTC patients.

Methods: Patients with PDTC diagnosed between January 1, 1985 and July 31, 2022 were identified using a thyroid cancer database at a medical center in Taiwan. Factors associated with distant metastasis and cancer-specific survival (CSS) were analyzed using binary logistic analysis and Cox regression, respectively. Survival analysis was conducted using the Kaplan-Meier method.

Results: The study cohort included 39 patients with PDTC, including 16 with distant metastasis on initial presentation, 5 with metastasis during the follow-up period, and 18 with no evidence of metastasis. Older age (≥ 45 years) was significantly associated with a higher risk of distant metastasis (odds ratio: 5.31; 95% confidence interval: 1.27-22.2; P = 0.018), while sex, tumor size, T stage, and N stage were not associated with distant metastasis. Patients with metastatic PDTC, either diagnosed at presentation or developing during follow-up, had poorer 5-year CSS rates (55.0% and 40.0%, respectively) than those without metastasis (5-year CSS, 93.8%) (P = 0.001 for both comparisons).

Conclusion: Older patients with PDTC have an increased risk of distant metastasis. Patients with metastatic PDTC, both diagnosed at presentation and developing during follow-up, have a dismal prognosis.