The presentation, natural history and outcome of T1 a/b thyroid cancer with regard to new grading systems

The seventh edition tumor, node metastasis (TNM) classifies tumors <10 mm as T1a and tumors between 10 mm and 20 mm as T1b. Previous editions of the TNM staging system did not differentiate these lesions. We compare new classification in terms of presentation and outcome.

Early thyroid cancers that were previously staged under the TNM sixth edition were re-staged using the TNM seventh edition to identify whether the new staging system differentiated lesions in terms of presentation and outcome. Differences in presentation, rates of recurrent disease and surgical complications were recorded and compared.

Of 1,415 thyroid operations, 369 were for malignant disease and there were 220 papillary carcinomas. There were 35 T1a/b lesions accounting for 11% of malignancies with no increasing incidence. Reclassification showed 64% T1a and 36% T1b lesions. There were no differences in presentation. Outcomes in terms of persistent or recurrent disease were the same after median follow up was 6.8 years.

Isolated T1a/b thyroid cancer made up only a small proportion of malignancies, the majority of which were discovered incidentally. We have not seen the increase in early lesions reported elsewhere. In our series, the seventh TNM edition did not differentiate early lesions and we ultimately feel that parameters other than size of primary lesion are likely to be of greater importance in determining prognosis.