mTOR signaling pathway in penile squamous cell carcinoma: pmTOR and peIF4E over expression correlate with aggressive tumor behavior

Abstract

Purpose: Penile squamous cell carcinoma is a rare neoplasm associated with a high risk of metastasis and morbidity. There are limited data on the role of the mTOR signaling pathway in penile squamous cell carcinoma carcinogenesis and tumor maintenance. We assessed a possible role for mTOR signaling pathway activation as a potential predictive biomarker of outcome and a therapeutic target for penile cancer.

Material and methods: A cohort of 67 patients diagnosed with invasive penile squamous cell carcinoma from 1987 to 2010 who had known HPV status were selected for study. Tissue microarrays were constructed with 67 primary penile squamous cell carcinomas, matched normal tissues and 8 lymph node metastases. Immunohistochemical staining was performed for p53, pmTOR, pERK, p4E-BP1, eIF4E and peIF4E. Expression was evaluated using a semiquantitative H-score on a scale of 0 to 300.

Results: Expression of pmTOR, p4E-BP1, eIF4E and peIF4E was increased in penile tumors compared with matched adjacent normal tissues, indicating activation of the mTOR signaling pathway in penile tumorigenesis. Over expression of pmTOR, peIF4E and p53 was significantly associated with lymph node disease. peIF4E and p53 also correlated with a poor outcome, including recurrence, metastasis or disease specific death. In contrast, pERK and p4E-BP1 were associated with lower pT stages. pmTOR and intense p53 expression was associated with HPV negative tumors.

Conclusions: Activation of mTOR signaling may contribute to penile squamous cell carcinoma progression and aggressive behavior. Targeting mTOR or its downstream signaling targets, such as peIF4E, may be a valid therapeutic strategy.

Keywords: 4E-BP1; ERK; HPV; MAPK; MAPK-interacting protein kinase; MNK; PI3K; SCC; TMA; TP53; biological markers; carcinoma; eIF4E; eukaryotic translation initiation factor 4E; eukaryotic translation initiation factor 4E-binding protein 1; extracellular regulated kinase; high risk HPV; hrHPV; human; human papillomavirus; immunohistochemistry; mTOR; mTOR protein; mammalian target of rapamycin; mitogen activated protein kinase; p; penis; phosphatidylinositol 3-kinase; phosphorylated; squamous cell; squamous cell carcinoma; tissue microarray; tumor protein 53 gene.