P53 PROTEIN, PCNA STAINING, AND DNA CONTENT IN FOLLICULAR NEOPLASMS OF THE THYROID-GLAND

Forty-nine follicular adenomas and II follicular carcinomas of the thy roid were investigated by immunohistochemistry for the expression of p 53 protein and proliferating cell nuclear antigen (PCNA). The DNA ploi dy and the S-phase fraction (SPF) of the neoplasms were analysed by fl ow cytometry. Twelve adenomas (24 per cent) and six carcinomas (55 per cent) were DNA non-diploid (P=0.07). The carcinomas had a higher prol iferation rate than the adenomas when assessed either by SPF size (med ian 9.9 per cent vs. 2.9 per cent, P=0.0003) or by PCNA staining inten sity (P<0.0001). Some scattered nuclei in two (4 per cent) adenomas an d in three (27 per cent) carcinomas stained positively for p53 (P=0.04 ). The two adenomas with positive staining for p53 were subserially se ctioned, but no signs of invasion were found; both patients are alive and well 6 and 7 years after surgery. One of the two adenomas showing positive p53 nuclear staining was DNA aneuploid, and both were positiv e in PCNA staining, but their SPFs were low (2.1 and 3.3 per cent). We conclude that p53 protein expression is not confined to follicular ca rcinomas; scattered p53-positive cells may also be present in histolog ically and clinically benign follicular adenomas. Because both follicu lar adenomas and carcinomas may be DNA aneuploid and their SPF and PCN A staining distributions overlap, the distinction between follicular a denoma and carcinoma should still be based on histological criteria.