Two major pathways of penile carcinogenesis: HPV-induced penile cancers overexpress p16ink4a, HPV-negative cancers associated with dermatoses express p53, but lack p16ink4a overexpression.

Background: Penile squamous cell carcinomas (SCC) arise either through transforming infections with human papillomavirus (HPV) or independent of HPV, often in the background of lichen sclerosus (LS) and lichen planus (LP). Despite impact on therapy and prognosis, etiologic stratifications are missing in most histological diagnoses and publications about penile cancers/precursors.

Objective: Classification of penile lesions into HPV-induced or HPV-negative via immunohistochemical demonstration of p16(ink4a) overexpression, a surrogate marker for transforming HPV-high-risk infections, and p53 expression in the absence of p16(ink4a) overexpression.

Methods: Archival formalin-fixed material of 123 invasive penile cancers and 43 pre-invasive lesions was evaluated for the presence of LS, LP, 28 HPV genotypes, and expression of p53 and p16(ink4a).

Results: Seventy-two of 123 SCCs and 33 of 43 pre-invasive lesions showed p16(ink4a) overexpression independent of HPV-HR genotypes involved; 66 of 72 SCCs and 29 of 43 precursor lesions revealed a single HPV-high-risk-genotype (HPV-HR16 in 76% followed by HPV33, HPV31, HPV45, HPV18, HPV56); 5 of 72 SCCs and 4 of 43 precursor lesions revealed multiple HPV-HR-genotypes. One SCC revealed HPV-LR and HR-DNA. Fifty-one of 123 SCCs and 10 precursor lesions were p16(ink4a) negative, but showed nuclear p53 expression in tumor cells and basal keratinocytes. Forty-nine of 51 SCCs and 10 of 10 precursor lesions lacked HPV DNA. Two of 51 SCCs contained HPV18 and HPV45 DNA, respectively, but p16(ink4a) negativity classified them as non-HPV-induced. Twenty-seven of 51 SCCs showed peritumoral LS, 13 of 51 SCCs showed peritumoral LP, and 11 SCCs revealed no peritumoral tissue. Histologically, HPV-negative precursors showed hyperkeratotic, verrucous, atrophic, and basaloid differentiation.

Limitations: This was a retrospective study.

Conclusions: p16(ink4a) overexpression identifies HPV-HR-induced penile carcinogenesis independent of HPV-HR genotype. p53 expression along with p16(ink4a) negativity identifies HPV-negative cancers. Correct etiologic classification of penile lesions during diagnostic work-up allows optimal therapy decisions.