Histologic trends in thyroid cancer 1969-1993: a clinico-pathologic analysis of the relative proportion of anaplastic carcinoma of the thyroid.

Background: It was observed that new presentations of anaplastic carcinoma of the thyroid had become infrequent in the last two decades.

Methods: All cases of thyroid cancer seen at our centre between 1969-1993 (n = 2921) were classified as papillary 49%, follicular 34%, medullary 7.5%, anaplastic 4.7%, and other 4.8%. The total number of thyroid cancers show a 3.5-fold rise.

Results: The differentiated thyroid cancers show a significant rising trend as against the relative proportion of anaplastic carcinoma, which shows a significant decline (P = 0.002). Clinicopathologic data on 124 patients of anaplastic carcinoma revealed 50% patients had either long-standing goitres, previous thyroid abnormalities, or associated differentiated thyroid carcinoma on histology.

Conclusions: The decline in the relative proportion of anaplastic carcinoma may in part be explained by the clinicopathologic findings or it may be attributed to histological reclassification.