Epidermal growth factor receptor immunohistochemical reactivity in patients with American Joint Committee on Cancer stage IV colon adenocarcinoma: Implications for a standardized scoring system

BACKGROUND. An epidermal growth factor receptor (EGFR) immunohistochemical detection system currently is being developed. The current study attempts to address background EGFR reactivity issues before determining the optimum EGFR scoring system. METHODS. Tissue sections from 102 patients with T3N1-2M1 colon adenocarcinoma were stained with a prototype EGFR detection system. The number of cases, location, percentage, and intensity of reactive cells (0+ [none] to 3+ [strong]) were scored and compared with the length of survival. RESULTS. Approximately 75.5% of the adenocarcinoma cases had EGFR reactivity; 31.4% of the tumors had 3+ reactivity in 10-50% of the neoplastic cells and 3.9% had 3+ reactivity in > 50% of cells. Increased numbers of reactive cells per case predominantly resulted from increased 3+ reactivity. The mean percentage of 2+ (moderate) and 3+ reactive cells per case increased in the regions of deepest invasion. The mean percentage of 3+ reactivity per case was significantly greater in the deepest tumor region compared with the superficial region (16.9% vs. 7.9%; P = 0.004). EGFR reactivity in metastases appeared to have the strongest correlation with reactivity in the deep regions of colon adenocarcinoma. An increasing percentage of 2+ and 3+ or 3+ only reactivity in the deep region was found to have the strongest correlation with decreased survival (P = 0.0252). CONCLUSIONS. EGFR reactivity of 2+ and 3+ may provide a framework for a scoring system. It may be important to evaluate EGFR reactivity in the deepest region of tumor invasion because this region appears to contain the largest percentage of 3+ reactive cells and appears to have the strongest correlation with survival length and EGFR reactivity in lymph node and liver metastases.