P126. Expression of GNA12 and its role in oral cancer

Introduction: The phosphatidylinositol 3-kinase (PI3K) signaling pathway is integral to cell growth, proliferation and survival, and is upregulated in multiple human cancers. Several oncogenes and tumor suppressors within this pathway are altered by mutation, amplification or deletion, and are currently being investigated as therapeutic targets in ongoing clinical trials for head and neck and other solid cancers. The pattern of genetic alteration has not been characterized in oral cavity squamous cell carcinoma (OCSCC). Objective: Our objective was to comprehensively analyze the pattern of mutational and copy number alteration in this pathway in OCSCC. Methods: After IRB approval, DNA was extracted from 32 microdissected frozen OCSCC samples and matched normal tissues. Highthroughput sequencing of 25 component genes of the PI3K pathway was performed. Three integrated sequence assemblies were screened for non-polymorphism coding mutations, which were independently validated on PCR. Array comparative genomic hybridization (aCGH) was then performed on the Agilent 1 M platform. The RAE computational framework was used for segmentation and identification of regions of statistically significant copy number alteration (CNA), which were then validated with qPCR. Immunohistochemistry of downstream proteins was used to confirm pathway activation. Results: Among the 25 component genes in the PI3K pathway, activating mutations were identified in PIK3CA in 6.3% of samples. Copy number gain was present in 15 genes (including PIK3CA in 45.2%), and loss in 4 genes (including PTEN in 12.9%). Altogether, 74% of tumor samples contained either activating mutations or CNAs within the PI3K pathway. Tumors with PIK3CA mutation or EGFR amplification had a significantly higher rate of copy number alterations in the PI3K pathway. Conclusions: In the first comprehensive mutational and copy number analysis of the 25 component genes of the PI3K pathway in cancer, we report a low frequency of somatic mutations, and high frequency of copy number alteration, in OCSCC. In contrast to colorectal, breast, ovarian, and brain cancers, copy number alteration, not mutation, appears to be the main source of pathway activation. These findings may have relevance to therapeutics targeting tumors in which the PI3K pathway is dysregulated, or in which PI3K pathway activation mediates resistance to EGFR inhibition.