Primary tumour diameter as a risk factor for advanced disease features of differentiated thyroid carcinoma

Abstract

Objective: To study the relationship between primary tumour size and the risk of advanced disease features (multifocal or locally invasive disease, lymph-node or distant metastases) in differentiated thyroid carcinoma (DTC).

Design: A retrospective chart review study.

Patients: The study sample comprised 935 papillary (PTC) and 291 follicular thyroid carcinoma (FTC) patients treated in our hospital from 1978 to 2007.

Measurements: Kaplan-Meier analyses and log-rank tests were performed to calculate tumour size-adjusted cumulative risk of advanced disease features.

Results: Accounting for primary tumour diameter, there were no significant differences in cumulative risks of multifocal carcinoma (P = 0.12) or distant metastases (P = 0.49) between PTC and FTC. PTC showed higher cumulative risks of local invasion (P < 0.0001) or lymph-node metastases (P < 0.0001). The cumulative risk of tumour multifocality increased 5%/cm of primary tumour diameter. The cumulative risk of local invasion or lymph-node metastases in PTC and of distant metastases in DTC increased exponentially at a threshold tumour diameter of 10 mm. In FTC, lymph-node metastases are associated almost exclusively with primary tumours showing extrathyroidal growth.

Conclusions: Starting with a 1 cm primary tumour diameter, increasing tumour size is associated with an exponentially increasing risk of local invasion or lymph-node or distant metastases of DTC. The current classification of carcinomas < 2 cm as T1 is therefore questionable.