Are Possible Risk Factors for Differentiated Thyroid Cancer of Prognostic Importance?

Objective: The only established risk factor for differentiated thyroid cancer (DTC) is ionizing radiation. How ionizing radiation and other possible risk factors for DTC influence the prognosis has not extensively been investigated. We studied if factors such as smoking, number of children, previous thyroid disorders, previous radiotherapy toward the neck, family history of thyroid diseases, and malignancies influenced survival for patients with DTC. Design: A nested case-control study was conducted within the cohort of all patients diagnosed with DTC in Sweden between 1958–1987. Cases consisted of patients who died from DTC. One control, matched by age at diagnosis, gender, and calendar period was randomly selected from the risk set for each case. Information of risk factors was collected from the medical records. Associations between these factors and prognosis were assessed using conditional logistic regression. Main outcome: Smokers had a borderline significant increased risk of dying from DTC. Previous radiotherapy towards the neck region had no prognostic implication. A family history of DTC influenced prognosis although not significant due to few cases. The remaining risk factors studied did not influence survival. Conclusions: In conclusion, smokers seemed to have a worsened prognosis compared to nonsmokers and a family history of thyroid cancer had a nonsignificant negative effect on survival.