EGFR belongs to a family of four related receptors that includes the EGFR (HER1), ERBB2, HER3, and HER4 receptors . The EGFR gene is located in the short arm of human chromosome 7 and produces a glycoprotein with a molecular weight of 170 kDa with high affinity for the EGF ligand . EGFR mediates multiple signal transduction pathways and, thereby, connects extracellular signaling to intracellular changes in gene expression that modulate cellular growth and differentiation. Currently, EGFR and ERBB2 are the best characterized of the HER family receptors. However, little is known regarding the expression and function of these receptors in gastric cancer.
In recent years, interest has grown in understanding the relationship between the biological characteristics of gastric cancer and the association of these characteristics with the clinical outcomes of the disease. Current studies have focused on understanding the molecular basis of gastric cancer in order to help achieve accurate diagnoses and to better choose effective treatment options. With the advent of novel targeted therapeutics, these molecular characteristics may be important for obtaining more effective therapeutic outcomes. Presently, much of the available knowledge regarding EGFR and ERBB2 expression as well as their biological function in gastric cancer has come from countries other than China. Research techniques for characterization of EGFR and ERBB2 expression have included immunohistochemistry (IHC), chromogenic in situ hybridization (CISH), and FISH. Using kits approved by the United States Federal Drug Administration for IHC (HercepTest™ and EGFR pharmDx™) and FISH (Path Vysion™), we have analyzed EGFR and ERBB2 protein expression and gene status in Chinese gastric cancer patients in order to provide more accurate reference data for future studies in the Chinese population.
EGFR and ERBB2 expression in gastric cancer has been reported in many past studies. IHC was first used in 1986 to detect ERBB2 expression in gastric cancer , which was followed by a large number of similar reports. Reported rates of ERBB2 gene expression in gastric cancer range were from 9% to 38%. Moreover, the correlation between EGFR/ERBB 2 expression in gastric cancer and prognosis remains controversial. In the present study, the ERBB2 protein was expressed in 42.0% (29/69) of gastric tumors, and ERBB2 gene amplification occurred in 20.3% (14/69) of tumors. Of 41 patients with lymph node metastases, ERBB2 gene amplification was present in 24.4% (10/41) of the cases. The EGFR protein was expressed in 52.2% (36/69) of gastric tumors, and EGFR gene amplification occurred in 29.0% (20/69) of tumors. Of patients with lymph node metastases, EGFR gene amplification was present in 34.1% (14/41) of the cases. These results suggest that ERBB2 and EGFR gene amplification are positively associated with ERBB2 and EGFR protein expression. Furthermore, a higher frequency of ERBB2 and EGFR gene amplification is present in gastric cancer patients with lymph node metastases. EGFR and ERBB2 expression in gastric epithelial cells are indicators of malignancy and may prove useful as markers for poor prognosis in gastric cancer.
At present, pathological examination is primary method used to assess the ERBB2 and EGFR status of tumor cells. In particular, IHC and FISH are commonly used in clinical settings. IHC is currently the most widely-used method, and kits are commercially-available for semi-quantitative detection of both ERBB2 and EGFR. Importantly, the higher levels of ERBB2 expression are associated with improved benefit of ERBB2-targeted anticancer drugs . Application of IHC to evaluate the expression of ERBB2 in tumor cells has limitations, as the determination of staining is partially subjective, as opposed to strictly quantitative. In contrast, results from the FISH are substantially less subjective than IHC, while maintaining sensitivity and specificity. Furthermore, the quantitative nature of FISH results can effectively reduce operator interference and inter-laboratory variations . In the present study, FISH revealed that ERBB2 gene amplification was present in 4 of 4 cases with an IHC score of 3+, in 7 of 9 cases with an IHC score of 2+, and in only 3 of 16 cases with an IHC score of 1+. These results indicated that a statistically significant difference in ERBB2 gene amplification was present between the high (2+ and 3+) and low (1+) IHC score groups (P < 0.05). Similar results were observed with respect to EGFR gene amplification. EGFR gene amplification was observed in 5 of 5 samples with an IHC score of 3+, in 10 of 11 samples with a score of 2+, and in 5 of 20 samples with a score of 1+, which represented a significant difference between the high (2+ and 3+) and low (1+) scores (P < 0.05). Based on these results, the FISH assay could prove to be truly valuable for determination of ERBB2 and EGFR expression in clinical practice.
In recent years, new developments in cancer biology have led to the emergence of novel molecular-targeted therapeutics. These targeted drugs selectively act on cancer cells at the molecular, biochemical, and genetic levels, specifically targeting abnormal cells, with minimal effects on the function of normal cells. For example, EGFR inhibitors have been used to block EGFR activity and, thereby, increase the radiosensitivity of tumor cells . This phenomenon can lead to improvement of the efficacy of radiotherapy, likely because inhibition of EGFR signaling in tumor cells decreases cell proliferation, accelerates apoptosis, interferes with the cell cycle, and extends the time required for DNA repair after radiation . In the present study, FISH analysis revealed that EGFR gene amplification was present in 24.6% of the cases analyzed, and IHC showed that the EGFR protein was expressed in 52.2% of the cases. These results suggest that in some radiation-resistant gastric cancer cases, targeting of EGFR for radiation sensitization therapy may have important clinical value.
Co-expression of ERBB2 and EGFR may have synergistic effects on the progression of gastric cancer . ERBB2 gene amplification was observed in20.3% (14/69) of gastric cancer patients, including 24.4% (10/41) of the 41 patients with lymph node metastases and only 7.1% (2/28) of patients without lymph node metastases, representing a significant difference (P < 0.05). EGFR gene amplification was present in 29.0% (20/69) of gastric cancers, including 34.1% (14/41) of patients with lymph node metastases and 10.7% (3/28) of patients without lymph node metastases, again representing a significant difference (P < 0.05). ERBB2 and EGFR gene amplification were also significantly related. Increased ERBB2 copy number and gene amplification were present in a total of 57.9% (40/69) of samples. However, Both ERBB2 and EGFR gene amplification of gastric tumors were 3 cases (4.3%), but abnormalities both ERBB2 and EGFR gene copy number were present in 36.2% of samples. These results suggest that alterations in ERBB2 or EGFR gene status in gastric cancer are common events that frequently occur within the same tumor.
In summary, ERBB2 and EGFR are transmembrane tyrosine kinases that can promote tumorigenesis and tumor progression. Expression of ERBB2 and EGFR appear to be closely related, and one or both proteins are frequently overexpressed in gastric epithelial cancer cells. Furthermore, the degree of expression is correlated with tumor invasion, progression, and patient survival, suggesting that these genes may represent important indicators of poor prognosis. EGFR overexpression in gastric cancer commonly leads to radiation resistance. Therefore, EGFR-targeted radiosensitization treatments may have important clinical value for treatment of gastric cancer.