GRB7 Expression and Correlation With HER2 Amplification in Invasive Breast Carcinoma

Growth factor receptor-bound protein 7 (GRB7) gene is located adjacent to the HER2 gene on the 17q12-21 amplicon, is often coamplified with HER2 in a subset of breast cancers, and has been implicated in resistance to anti-HER2 and antiestrogen therapy. This study investigated the correlation of GRB7 expression by immunohistochemistry with HER2 expression, HER2 amplification, increased chromosome 17 copy number, and other prognostic and predictive factors in invasive breast cancer, including histologic grade, pathologic stage, and ER, PR, and p53 status. Paraffin-embedded samples of 188 invasive breast carcinomas with documented HER2, ER, and PR testing were collected and divided into 3 groups: cases positive for HER2 overexpression/gene amplification (n= 60), negative for HER2 overexpression (n= 97), and cases with increased chromosome 17 copy number without HER2 amplification (n= 31). GRB7 expression was evaluated on all 188 cases. In addition, p53 immunohistochemistry was performed on 13 HER2+/GRB7+ cases and 39 HER2+/GRB7- cases. GRB7 expression correlated strongly with HER2 overexpression. GRB7 expression was present in 20/60 (33.33%) of HER2+ cases, compared with 1/97 (1.03%) HER2- cases, and 1/31 (3.22%) increased chromosome 17 copy number cases (P < 0.0001). In HER2+ cases, GRB7 expression was found to correlate significantly with a greater degree of HER2 amplification. The mean +/- SEM HER2 copy number was 21.14 +/- 2.59 in GRB7+ cases, compared with 9.8 +/- 1.38 in GRB7- cases (P = 0.0001). GRB7 expression correlated significantly with ER negativity (P = 0.012) and p53 positivity (P = 0.03). GRB7 expression did not correlate with histologic grade, pathologic stage, or PR expression. Our data shows that GRB7 expression in invasive breast cancer correlates with markers of a more aggressive phenotype, including HER2 overexpression, a greater degree of HER2 amplification, ER negativity, and p53 positivity.