Purposes: We investigated the influences of prognostic factors on long-term survival of patients with follicular thyroid cancer (FTC) based on all-cause mortality and two exclusive causes of death, FTC and non-FTC.
Methods: In this retrospective cohort study, we collected data of 204 patients with FTC diagnosed between 1985 and 2007 at National Taiwan University Hospital. For all-cause mortality, Cox proportional hazards models were used to estimate hazard ratios for prognostic factors. Cause-specific hazard and cumulative incidence function models were used to determine the influences of prognostic factors on FTC and non-FTC death, respectively. The dynamic processes of distant metastases and locoregional recurrences were included as time-varying factors in all models.
Results: The cumulative incidence of all-cause death was 24% and 45% at 10 and 20-years, respectively. Multivariate analyses identified that distant metastases, locoregional recurrences, and positive surgical margins were significant independent risk factors for overall survival, hazard, and cumulative incidence of FTC death. Age at diagnosis >60 years increased the risks of all-cause and non-FTC death as well as cumulative incidence of non-FTC death. Tumor size >4 cm had a harmful effect on overall survival. Female patients had higher risk and cumulative incidence of FTC death, but male patients had a higher cumulative incidence of non-FTC death. Lymph node metastases significantly increased the cumulative incidence of FTC death.
Conclusion: Dynamic distant metastases and locoregional recurrences were the most dominant risk factors influencing FTC-specific hazard and cumulative incidence for FTC death by accounting for non-FTC death as a competing risk for FTC patients.
Keywords: Distant metastasis; Follicular thyroid cancer; Locoregional recurrence; Prognosis; Thyroid cancer.
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