Significance of HER2 protein expression and HER2 gene amplification in colorectal adenocarcinomas

BACKGROUND: Human epidermal growth factor receptor 2 (HER2) is an oncogenic driver, and a well-established therapeutic target in breast and gastric cancers. While the role of HER2 as a prognostic biomarker in colorectal adenocarcinomas (CRCs) remains uncertain, its relevance as a therapeutic target has been established. We undertook the present study to evaluate the frequency of HER2 expression in CRC and to correlate it with various clinicopathological variables. AIM: To correlate HER2 protein expression and HER2 gene amplification with clinicopathological features and survival in surgically resected CRC. METHODS: About 1195 consecutive surgically resected CRCs were analyzed by immunohistochemical staining (IHC) to assess HER2 protein expression, and 141 selected tumors were further evaluated by fluorescence in situ hybridization (FISH) to assess HER2 gene amplification. Follow-up information was available for 1058 patients, and using this information we investigated the prevalence of HER2 protein overexpression and gene amplification in a large series of surgically resected CRCs, and evaluated the relationship between overexpression and clinicopathological parameters and prognosis. RESULTS: HER2 IHC scores of 3+, 2+, 1+, and 0 were seen in 31 (2.6%), 105 (8.8%), 475 (39.7%), and 584 (48.9%) tumors, respectively. HER2 gene amplification was seen in 24/29 tumors with an IHC score of 3+ (82.8%; unreadable in 2/31), 12/102 tumors with an IHC score of 2+ (11.8%; unreadable in 2/104), and 0 tumors with IHC score of 1+ (0/10). HER2 gene amplification was seen in 36/1191 tumors (3.0%; unreadable in 4/1195). Among the tumors with HER2 IHC scores of 3+ and 2+, the mean percentage of tumor cells with positive IHC staining was 90% (median 100%, range 40%-100%) and 67% (median 75%, range 5%-95%), respectively (P < 0.05). Among tumors with IHC scores of 2+, those with HER2 gene amplification had a higher number of tumors cells with positive IHC staining (n = 12, mean 93%, median 95%, range 90%-95%) than those without (n = 90, mean 70%, median 50%, range 5%-95%) (P < 0.05). HER2 gene status was significantly associated with distant tumor metastasis and stage (P = 0.028 and 0.025). HER2 protein overexpression as measured by IHC or HER2 gene amplification as measured by FISH was not associated with overall survival (OS) or disease-specific survival for the overall group of 1058 patients. However, further stratification revealed that among patients with tubular adenocarcinomas who were 65 years old or younger (n = 601), those exhibiting HER2 gene amplification had a shorter OS than those without (mean: 47.9 mo vs 65.1 mo, P = 0.04). Among those patients with moderately to poorly differentiated tubular adenocarcinomas, those with positive HER2 tumor IHC scores (2+, 3+) had a shorter mean OS than those with negative HER2 IHC scores (0, 1+) (47.2 mo vs 64.8 mo, P = 0.033). Moreover, among patients with T2 to T4 stage tumors, those with positive HER2 IHC scores also had a shorter mean OS than those with negative HER2 IHC scores (47.1 mo vs 64.8 mo, P = 0.031). CONCLUSION: HER2 protein levels are correlated with clinical outcomes, and positive HER2 expression as measured by IHC confers a worse prognosis in those patients 65 years old or younger with tubular adenocarcinomas.