Co-existent anaplastic and well differentiated thyroid carcinomas: a nuclear DNA study.

Clonal transformation of well differentiated follicular or papillary carcinomas has been suggested as a mechanism by which anaplastic carcinomas of the thyroid might arise. Of 126 cases of anaplastic (giant cell) carcinomas, 17 (13.5%) contained histologically well differentiated tumour foci within or adjacent to the high grade malignant anaplastic tumour. Cytophotometric DNA analysis after Feulgen staining was performed on 11 cases in order to evaluate ploidy of the anaplastic and the well differentiated tumour cells. The majority of these co-existent carcinomas (9/11) were papillary. All 11 anaplastic carcinomas demonstrated an aneuploid DNA pattern which correlated with a poor clinical outcome (7 of 11 died of disease in less than 6 months). In contrast six co-existent papillary and one co-existent follicular tumours were diploid. These data show that the co-existence of anaplastic and well differentiated carcinoma occurs only rarely and when it occurs only one third of the well differentiated tumours contain aneuploid tumour cells. This suggests that in the majority of cases of anaplastic thyroid carcinoma the malignant cells arise de novo rather than through clonal transformation of well differentiated carcinomas.