Risk factors and outcomes of metastatic poorly differentiated thyroid carcinoma

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

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.

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.

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).

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.