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

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).

A retrospective chart review study.

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

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

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.

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.