Case Number : Case 1570 - 01 July Posted By: Guest

Porocarcinoma. 

Porocarcinoma.

Nice p16 expression highlighting the malignant nature of the intraepidermal poromatous component...Dr Carr what do you think about the p53 usefulness in order to distinguish between benign and malignant lesions? I've studied something about this but i'm a bit confuse. Thanks for this very interesting case!

Agree with porocarcinoma

Case kindly received in referral by Dr Miroslav Radojkovic.

In view of the purely rounded borders I called this porocarcinoma / malignant hidroacanthoma in situ.  Porocarcinoma in situ can have rather deep pushing, but entirely circusmcript, borders as in this case.

I find p53 (diffuse strong nuclear or completely negative, null phenotype, with good internal controls) quite useful being nearly 99% specific for malignancy (I've seen diffuse strong p53 once only in a lesion I called benign, an otherwise typical pilomatrixoma).  It is not so sensitive however (circa 50% for surface tumours - no doubt UV induced mutations mainly). Beware you can have quite prominent weak and moderate staining as wild-type up-regulation (but maturing central cells will be weak/negative) so my cut-off for diffuse strong is high e.g. ~80% nuclei with strong staining - personal experience. In clonal lesions I find the combination of p16, Ki67 and p53 to be highly useful in distinguishing benign from malignant.  You can see quite a variation of p16 and p53 in individual cases (p16+, p53 wild; p16-, p53 mutant/null, p16+/p53 mutant/null)

This case did have a benign hidroacanthomatous component - not illustrated.