Importance of tumour size in papillary and follicular thyroid cancer.
BACKGROUND: The most controversial change in the new pathological tumour node metastasis (pTNM) classification of thyroid tumours is the extension of the pT1 classification to include tumours up to 20 mm. METHODS: Four hundred and three patients with pT1 or pT2 differentiated thyroid carcinomas were divided into three groups according to tumour diameter (group 1, 10 mm or less; group 2, 11-20 mm; group 3, 21-40 mm). They were analysed retrospectively with respect to carcinoma-specific and disease-free survival. RESULTS: No patient in group 1 died from papillary thyroid carcinoma, compared with three patients in group 2 and six in group 3. There was a statistically significant difference in carcinoma-specific survival between groups 1 and 2 (P = 0.033). Two patients in group 1, six in group 2 and eight in group 3 developed recurrence. The difference in disease-free survival between groups 1 and 2 was significant (P = 0.025). One patient in group 1, three in group 2 and four in group 3 died from follicular thyroid carcinoma, but there were no significant differences in survival between the three groups. CONCLUSION: Extension of the pT1 classification to cover all tumours up to 20 mm does not appear to be justified for papillary thyroid carcinoma.