Disease-free survival in papillary and follicular thyroid carcinoma

Abstract

SummaryT stage was redefined for patients with differentiated thyroid carcinoma (DTC) between the 5th and 7th versions of the UICC tumour classification system. Patients, methods: 636 patients (486 women, 150 men; mean age 49.1 ± 15.6 years, mean follow-up 4.6 years) who had been treated with ablative radioiodine therapy after thyroidectomy for papillary (PTC) or follicular thyroid carcinomas (FTC) were retrospectively assessed on occurrence of locoregional recurrent disease, or cervical lymph node or distant metastases. Disease-free survival was calculated from initial T stage, classified according to both versions of the UICC staging system and compared with the prognostic value of primary tumour size. Kaplan-Meier method and two measures of explained variation, (1) R2 based on the (partial) likelihood ratio statistic of the Cox proportional hazards model and (2) a model-free variant of a distance measure proposed by Schemper had the aim to detect the most advantageous classification. Results: Of the 508 patients with PTC, 11 (2.2%) developed a local recurrence, 37 (7.3%) cervical lymph node and 23 (4.5%) distant metastases, 3 (2.3%), 8 (6.3%), and 18 (14.1%) were the numbers for the 128 FTC patients respectively. The two classification systems yielded an equal count of statistically significant differences regarding disease-free survival in patients with PTC while UICC 7th classification appeared slightly advantageous in patients with FTC. Regarding explained variation the UICC 7th classification tended to be superior to the UICC 5th classification, both in PTC and FTC, however statistical significance was not reached. Conclusion: The primary tumour size significantly added to the prognosis regarding local cervical and distant metastases.