594 A novel form of cellular senescence induced by hyper-activation of the PI3K/Akt pathway

Abstract

Periocular sebaceous carcinoma is an aggressive neoplasm with significant morbidity and mortality. Its pathogenesis is poorly understood. It is only rarely associated with Muir-Torre syndrome. Previous studies from Asian countries, have suggested that human papillomavirus (HPV) infection plays a role in the pathogenesis and overexpression of p16INK4a, a surrogate marker of HPV infection, have also been reported. However, data from western countries seem contradictory. In order to clarify and explore the molecular and epigenetic basis of HPV, CDKN2A status and role of microsatellite instability in the development of periocular sebaceous carcinoma, 24 cases of periocular sebaceous carcinoma were analyzed for the expression of p16INK4a and mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) via immunohistochemistry. Nested polymerase chain reaction (PCR) and genechip HPV typing were used to detect HPV infection and decide its genotype when present. PCR amplification using a consensus primer pair was also performed to detect β-HPV. The methylation status of CDKN2A promoter region was studied by methylation-specific polymerase chain reaction. HPV-positivity was demonstrated in only one of our cases (HPV 16), while another case showed p16INK4a overexpression. All cases showed preserved expression of mismatch repair proteins. CDKN2A promoter hypermethylation was noted in nearly half of our cases (11/24) and was associated with younger patient age (P = .013). Our results showed that periocular sebaceous carcinoma is rarely associated with HPV and microsatellite instability. Higher frequency of CDKN2A promoter hypermethylation in younger patients implies a significant epigenetic role in tumor development in this age group.