Medullary carcinoma of the thyroid misdiagnosed as differentiated thyroid carcinoma.

Four patients are presented, who were initially diagnosed and treated for differentiated thyroid carcinoma, but subsequently discovered to have medullary carcinoma. We suggest that tumour histopathology needs to be carefully reviewed in all cases of thyroid cancer, especially those having atypical clinical or pathological features. This should be completed prior to further therapeutic intervention, such as the administration of ablative radioactive iodine.