For example, a study by Shia et al. found that only a small fraction (17 of 124 or 14%) of EGFR-positive (defined as 1+, 2+, or 3+) colorectal carcinomas detected by immunohistochemistry were associated with EGFR gene amplification (defined as >5 gene copies/nucleus) [19]. Here, EGFR is linked to colorectal carcinoma.