Clinically significant prognostic factors for differentiated thyroid carcinoma: a population-based, nested case-control study

BACKGROUND: Different scoring systems currently are being used to stratify patients with differentiated thyroid carcinoma (DTC) into risk groups. DTC is usually subdivided into papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC). The objective of the current study was to identify those factors that predict long-term unfavorable prognosis and to evaluate the predictive accuracy of the TNM staging system. METHODS: The authors conducted a nested case-control study within the cohort of all patients (n=5123) diagnosed with DTC in Sweden between 1958-1987 who survived at least 1 year after diagnosis. One control, matched by age at diagnosis, gender, and calendar period, was randomly selected for each case (patients who died of DTC). All patients were classified at the time of diagnosis according to the TNM staging system. The effect of prognostic factors on DTC mortality was evaluated using conditional logistic regression. RESULTS: Patients with widely invasive FTC experienced a significantly higher mortality compared with PTC patients. The grade of differentiation was found to influence mortality significantly. Patients with TNM Stage IV disease had a higher mortality rate compared with patients with Stage II disease (odds ratio OR]=9.1; 95% confidence interval 95% CI], 5.7-14.6). Patients with lymph node metastases experienced a higher mortality (OR=2.5; 95% CI, 1.6-4.1) and patients with distant metastasis at the time of diagnosis were found to have a nearly 7-fold higher mortality rate (OR=6.6; 95% CI, 4.1-10.5). Incomplete surgical excision was associated with higher mortality, particularly in patients with Stage I disease. CONCLUSIONS: In the current study, the following were found to be clinically significant prognostic factors for patients with DTC: histopathologic subgroup, TNM staging including lymph node metastases and distant metastases, and completeness of the surgical excision.