Abstract
Objectives: In differentiated thyroid carcinoma a larger tumour diameter is considered to indicate a poorer prognosis. This higher risk is most likely effectuated due to a higher rate of metastases and locally invasive growth in patients with larger carcinomas. The aim of this study is to study the relation between tumour size and the chance of multifocal carcinoma, locally invasive disease and lymph-node or distant metastases.
Materials and methods: The files of 935 papillary (PTC) and 291 follicular thyroid carcinoma (FTC) patients treated in our hospital since 1978 were reviewed. Kaplan-Meier analyses were performed to assess the cumulative risk related to increasing tumour size. Differences between survival curves were calculated using a log-rank test.
Results: Accounting for primary tumour diameter, there was no significant difference in cumulative risk for multifocal carcinoma (p=0.12), distant metastases (p=0.49) or death of thyroid carcinoma (p=0.46) between PTC and FTC. PTC showed a higher cumulative risk for distant lymph node metastases (p<0.0001) and extrathyroidal tumour growth (p><0.0001). The risk for tumour multifocality seems to be linearly increasing with a cumulative risk of 5 percent per cm. tumour growth, whereas the increase in cumulative risk shows an exponential trend with regard to locally invasive disease, nodular and distant metastases and cancer-specific death. The anchoring point on the x-axis of the curve for distant metastases was located at a threshold tumour diameter of 10 mm, which was also the case for extrathyroidal growth and the risk of lymph node metastases in PTC.
Conclusions: Increasing tumour size is related with an exponentially increasing risk of extrathyroidal tumour growth, lymph node and distant metastases. A tumour diameter > 1 cm seems to be related to a sharply increasing risk for such adverse findings. One can therefore question the current practice of classifying carcinomas > 1cm and <2cm as T1.