PTEN Gene Expression and Mutations in the PIK3CA Gene as Predictors of Clinical Benefit to Anti-Epidermal Growth Factor Receptor Antibody Therapy in Patients With KRAS Wild-Type Metastatic Colorectal Cancer

To determine biomarkers predictive of benefit to anti-EGFR (epidermal growth factor receptor) monoclonal antibodies in patients with KRAS wild-type metastatic colorectal cancer, we studied tumor tissue from patients who received these drugs. By focusing on the PI3K-mTOR-AKT-PTEN pathway, we concluded that PIK3CA-activating mutations and loss of PTEN expression are novel potential biomarkers that will lead to further refinement of therapy for these patients. Purpose: To identify novel genetic markers predictive of clinical benefit from epidermal growth factor receptor directed antibody therapy in patients with metastatic colorectal cancer. Patients and Methods: Seventy-six consecutive patients who received cetuximab or panitumumab, either alone or in combination with chemotherapy and with available tumor tissue were included. Tumor tissue was tested by pyrosequencing for mutations at known hot spots in the KRAS, BRAF, PIK3CA, PIK3R1, AKT1, and PTEN genes. PTEN promoter methylation status was analyzed by methylation-specific polymerase chain reaction, and expression was determined by immunohistochemistry (IHC). Forty-four patients had 4 weeks of therapy and were considered for clinical correlates. Results: Consistent with previous studies, KRAS gene mutations were associated with a shorter progression-free survival (PFS) and overall survival (OS). Among the patients with wild-type KRAS, preservation of PTEN expression and PIK3CA wild-type status was associated with improved OS (median OS, 80.4 vs. 32.5 weeks; hazard ratio, 0.33; P = .0008) and a trend toward improved PFS (median PFS, 24.8 vs. 15.2 weeks; hazard ratio, 0.51; P = .06), compared with PTEN-negative or PIK3CA-mutant tumors. PTEN methylation was more common in the metastatic samples than in the primary samples (P = .02). The simultaneous presence of methylation and mutation in the PTEN gene was associated with IHC negativity (P = .026). Conclusion: In addition to KRAS mutation, loss of PTEN expression (by IHC) and PIK3CA mutation is likely to be predictive of a lack of benefit to anti-EGFR therapy in metastatic colorectal cancer. PTEN promoter methylation and mutation status was predictive of PTEN expression and may be used as an alternative means of predicting response to EGFR-targeted therapy.