Impact of PI3K-AKT-mTOR Signaling Pathway Up-regulation on Prognosis of Penile Squamous-Cell Carcinoma: Results From a Tissue Microarray Study and Review of the Literature

Abstract Purpose To assess the prognostic value of PI3K-AKT-mTOR signaling pathway up-regulation in a contemporary cohort of penile squamous-cell carcinoma (PSCC) patients. Patients and Methods Tissue microarrays were constructed for 57 patients with invasive PSCC treated at our institution between 2000 and 2013. Immunohistochemical staining was performed for PTEN, AKT, and S6. Human papillomavirus (HPV) in-situ hybridization for high-risk subtypes was also performed. Biomarker expression was evaluated by a semiquantitative H score. Overall survival, disease-specific survival and recurrence-free survival stratified by biomarker expression (low vs. high) were estimated by the Kaplan-Meier method. Multivariable Cox regression models were used to determine predictors of mortality and recurrence. Results HPV in-situ hybridization was positive in 23 patients (40%). PTEN was down-regulated in 43 patients (75%), while phosphorylated-AKT (p-AKT) and phosphorylated-S6 (p-S6) were up-regulated in 27 (47%) and 12 patients (21%), respectively. In multivariable Cox regression models, patients with low expression of p-AKT had an increased risk of recurrence (hazard ratio [HR] = 3.95; 95% confidence interval [CI], 1.47-10.59; P  = .02), while those with low expression of p-S6 had an increased risk of overall mortality (HR = 6.15; 95% CI, 1.55-24.36; P  = .01). HPV status was an independent predictor of overall survival (HR = 6.99; 95% CI, 2.42-20.16; P P  = .002). Conclusion PI3K-AKT-mTOR signaling pathway up-regulation and HPV coinfection in PSCC are associated with favorable disease. mTOR pathway biomarkers along with HPV status may represent novel prognosticators for risk stratification of PSCC patients and may help guide treatment decisions and follow-up strategies. These findings require further investigation.