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Background: The epidermal growth factor receptor (EGFR) is a surrogate marker for basal-like breast cancer. A recent study suggested that EGFR may be used as a target for breast cancertreatment. Methods: A total of 706 invasive ductal carcinomas (IDC) of the breast were immunophenotyped, and 82 cases with EGFR protein expression were studied for EGFR gene amplification. Results: EGFR protein was expressed in 121 of 706 IDCs (17.1%); 5.9% were of luminal type, 25.3% of epidermal growth factor receptor 2 (HER-2) type, and 79.3% of basal-like tumors. EGFR gene amplification and high polysomy (fluorescent in situ hybridization [FISH]-positive) were found in 18 of 82 cases (22.0%); 41.2% of the HER-2+, EGFR+, cytokeratin 5/6– (CK5/6–) group, 11.2% of the HER-2–, EGFR+, CK5/6– group, and 19.1% of the HER-2–, EGFR+, CK5/6+ group. FISH-positive cases were detected in 8.3% of the EGFR protein 1+ expression cases, 15.9% of 2+ expression cases, and 38.5% of 3+ expression cases. In group 2, the tumors had a high Ki-67 labeling (>60%), but the patients showed better disease-free survival than those with tumors that co-expressed HER-2 or CK5/6. Conclusions: EGFR-directed therapy can be considered in breast cancer patients with EGFR protein overexpression and gene amplification, and its therapeutic implication should be determined in HER-2 type breast cancer patients.
