Differential diagnosis of keratoacanthomas and squamous cell carcinomas: diagnostic value of DNA image cytometry and p53 expression.

DNA-cytometry and immunohistochemistry with the anti-p53 antibody DO-1 was performed in 24 keratoacanthomas (KA) and 21 squamous cell carcinomas (SCC) (13 well-differentiated, 8 moderately differentiated) to establish the possible value of these methods for the differential diagnosis of both epithelial tumors. Aneuploidy was detected in 1 (4%) KA and 12 (57%) SCC (p < 0.05). In the latter tumors, histologic grade was associated with an abnormal DNA-content. Six (46%) well and 6 (75%) moderately differentiated SCC were shown to be aneuploid. Over-expression of p53 protein was found in 16 (76%) SCC and 14 (66%) KA (p > 0.05; not significant). However, quantification of p53 expression by evaluating both the intensity of immunostaining and the number of cells with over-expression by means of an immunoreactivity score (IRS) showed significant differences (p < 0.05). There was no correlation of p53 over-expression and aneuploidy in the tumors examined. The analysis of ploidy and immunostaining with anti-p53 antibodies may give useful additional information regarding the differential diagnosis of SCC and KA, if only aneuploidy or a high IRS are considered.