Prevalence of HER2 Positivity and Its Clinicopathological Correlation in Locally Advanced/Metastatic Gastric Cancer Patients in Malaysia

The International Agency for Research on Cancer (IARC) suggests that gastric cancer (GC) is the fifth most common cancer in the world based on its GLOBOCAN 2012 project data. Gastric cancer is also the third leading cause of cancer mortality in both sexes worldwide (723,000 deaths) [1]. The majority of patients with GC presents at an advanced stage and experiences significant morbidity and mortality [2]. The age-standardized incidence rate (ASR) of GC is about twice as high in men as in women [1].

More than 70% of GC cases are diagnosed in developing countries. More than 727,000 cases of GC were diagnosed in Asia in 2008 accounting for 11.9% of all the cancers diagnosed [3]. Nearly half the total global cases of GC occur in Eastern Asia, mainly in China [1]. The report issued by the National Cancer Registry, Malaysia, in 2006 showed that the total incidence of stomach cancer in the country was 3.9% [4]. However, the incidence of GC varies among people of Chinese, Malay, and Indian origin [5]. Higher rates of GC have been observed in the Chinese population compared to the Malay and Indian populations [6].

Human epidermal growth factor receptor 2 (erb2/HER2) is a member of the HER family and is a proto-oncogene encoded by erb2 on chromosome 17. It plays a major role in promoting cell proliferation and suppressing apoptosis and thus facilitates excessive or uncontrolled cell growth and tumorigenesis. Although HER2 expression was initially associated with breast cancer, it has now been implicated in advanced gastric and gastroesophageal junction cancer (GEC) [7]. While 15–25% of all patients with breast cancer have been found to be HER2 positive, the rate of HER2 positivity varies widely among patients with GC. HER2 positivity has been found to range from 6.8–34% on immunohistochemistry (IHC) and 7.1–42.6% on fluorescent in situ hybridization (FISH) in GC [8].

HER2 is a well-established therapeutic target in breast cancer [2]. Preclinical evidence attests to the significant antitumor efficacy of anti-HER2 therapies (particularly monoclonal antibodies) in GC [9]. Trastuzumab, an anti-HER2 humanized monoclonal antibody [10], already in use for prolonging overall survival and progression-free survival in patients with HER2-positive breast cancer, has now been shown to significantly prolong survival in patients with GC and GEC. Other agents that target HER2, including lapatinib, emtansine (T-DM1), and pertuzumab are also being developed and have demonstrated promising results in HER2-positive breast cancer [7]. The efficacy of lapatinib in combination with capecitabine and oxaliplatin was investigated in a randomized placebo-controlled phase III trial involving 545 patients with HER2-positive advanced gastroesophageal adenocarcinoma. The patients were randomly assigned to capecitabine and oxaliplatin plus lapatinib 1250 mg or placebo daily. The primary endpoint of the study was overall survival. There were no significant differences between the two groups in terms of overall survival although the lapatinib group demonstrated a significantly higher response rate compared to the placebo group [11]. The Trastuzumab for Gastric Cancer (ToGA) trial (a prospective phase III open-label trial) screened 3803 patients with GC/GEC for HER2 status with IHC and FISH test. Patients were considered eligible for the study if their tumor samples were scored as 3+ on IHC or if they were FISH positive (HER2/centromeric probe for chromosome 17 [CEP17] ratio ≥ 2). In this study, 810 patients were found to be HER2 positive. These HER2-positive patients, when treated with trastuzumab in combination with ongoing chemotherapy, showed significant improvement in overall survival as compared to patients who did not receive trastuzumab (13.8 vs. 11. 1 months; hazard ratio 0∙74; 95% CI 0∙60–0∙91; p = 0.0046). Post hoc analysis of two large subgroups, one with high HER2 expression (IHC 2+ and FISH positive or IHC 3+; n = 446) and the other with low HER2 expression (IHC 0 and FISH positive or IHC 1+ and FISH positive; n = 131) was performed. The analysis showed that patients whose tumors had high HER2 expression had a high overall median overall survival (16.0 months) with trastuzumab plus chemotherapy compared to chemotherapy alone (11.8 months) [12]. Thus, HER2 testing has emerged as a promising prognostic marker that could benefit patients with GC/GEC if coupled with an appropriate targeted therapy [2, 7, 10]. Studies conducted so far suggest the need for optimizing HER2 testing as appropriate interpretation of these test results could translate into delivery of optimal therapy. It has been reported that only patients with high levels of HER2 expression derive maximum benefit from trastuzumab therapy [2]. The European Medicines Agency has now recommended that Herceptin (trastuzumab) should be used only in patients with metastatic GC tumors that have HER2 overexpression defined by IHC2+ and a confirmatory ISH+ result, or IHC3+ determined by an accurate and validated assay [13].

A highly varied epidemiological presentation of GC/GEC warrants the conduct of well-designed studies in specific populations/ethnic groups to establish the association between HER2 overexpression and GC treatment. In a recently published study in Japanese patients with GC, tissue expression of HER2 was reported in 6.7% of the 105 patients screened [14].

According to the latest available cancer statistics in Malaysia (2007), 630 cases of GC have been recorded in the country [15]. However, no specific study data has correlated HER2 overexpression with the different stages of GC/GEC in the Malaysian population. A study examining the frequency of HER2 overexpression in GC/GEC in the Malaysian population would therefore provide valuable data unique to Malaysian patients and allow for cost-effective management of the cancer from the standpoint of early diagnosis and optimal therapeutic strategies. Hence, we conducted an observational study to examine the correlation of HER2 overexpression in GC/GEC with parameters such as basic demography, race, pathological subgroups, and site of origin in the Malaysian population.

The primary objective of the study was to determine the incidence of HER2 positivity in patients with locally advanced or metastatic GC and GEC in Malaysia. The secondary objective was to evaluate correlation of HER2 overexpression with demographic and clinicopathological parameters.

The human epidermal growth factor receptors play a central role in the pathogenesis of several human cancers due to their function in regulating cell growth, survival, and differentiation via multiple signal transduction pathways. HER2, which is expressed in many tissues, plays a major role in facilitating uncontrolled cell growth and differentiation. Most studies on HER2 have been carried out in patients with breast cancer. However, thanks to the increasing awareness of the clinical significance of HER2 biology, the role of HER2 in other cancers such as stomach, ovary, uterine serous endometrial carcinoma, colon, bladder, lung, uterine cervix, head and neck, and esophagus cancer has also been identified [16]. This has resulted in rigorous testing of gastric and GEC, notably with a view to improve survival outcomes.

HER2 overexpression in GC using immunohistochemistry (IHC) was first described in 1986 [9]. More than 20% of gastric cancers have demonstrated HER2 overexpression and/or amplification with the percentage increasing to 33% in GEC tumors [10]. In our study, HER2 positivity was evident in 24.6% of patients. Similar HER2 overexpression rates were reported in a Japanese study, where the rate of HER2 overexpression in 200 resected tumors was found to be 23%. In the same study, gene amplification by FISH was identified in 27.1% of the cases [17]. In our study, out of 56 samples, 44 (78.6%) were considered for gene amplification testing, out of which 40 (90.1%) samples showed gene amplification. Tumors with IHC3+ score showed 96.7% correlation with c-ERB-2 gene amplification, and 78.6% tumors with IHC2+ score showed c-ERB-2 gene amplification.

In our study, no statistically significant correlation was observed between HER2 positivity and age, race, tumor location, tumor differentiation, and TNM staging. However, a statistically significant correlation was observed between HER2 positivity and male gender (29.6%; p = 0.024), which may be attributable to the higher number of male patients in our study. Furthermore, gastric adenocarcinomas are more common in males [18]. Although statistically non-significant, HER2 expression was more common in Malay patients (46.7%) followed by patients of Indian origin (25%). Furthermore, studies have reported that HER2 expression is more frequent in GEC compared to GC [9]. In our study, the incidence of HER2 positivity was found to be greater in GEC than in gastric body cancers, but this finding did not reach statistical significance. This association has been confirmed by the ToGA study with a large number of patients which demonstrated HER2 positivity in 32 and 18% in GEC and GC, respectively. Several recent studies have demonstrated an association between HER2 expression and tumors with intestinal type histology. The contributing factors for HER2 overexpression in intestinal type GC are quite complex and require extensive investigation. The association between this oncogene and a specific histologic type indicates that certain characteristics may be preferentially expressed together. However, since not all intestinal type tumors are associated with HER2 expression, more than one factor may be involved [9]. However, in our study, HER2 expression was significantly more common in diffuse-type tumors (p < 0.001) than in intestinal type tumors.

Our study showed a non-significant association between HER2 expression and well differentiated tumors. Studies have shown both an association and nonassociation between HER2 overexpression and tumor differentiation. This discrepancy may be attributed to varying sample sizes and lower prevalence of HER2 in GC and GEC. Varying methods of evaluation and scoring schemes with different cutoff points before the establishment of standard guidelines may also have contributed [19]. However, no significant association was observed between HER2 expression and TNM staging.

Increasing evidence suggests that HER2 is an important biomarker of GC and GEC. Many studies have evaluated the association of HER2 status and prognosis in patients with GC. The findings have been inconsistent with some studies demonstrating a significantly worse prognosis in patients with HER2 positivity [20, 21] whereas others showing no association between the HER2 status and prognosis [22, 23]. A few studies have demonstrated a longer median overall survival in HER2-positive compared to HER2-negative patients [22, 24]. In a study by Nakajima et al., HER2 overexpression along with nodal metastasis was considered as one of the independent prognostic factors [25]. Hence, the relationship between HER2 status and prognosis in GC remains a subject mired in controversy [7].

In addition to being implicated in the pathogenesis of cancers, HER2 has also been evaluated as a therapeutic target. It has been successfully targeted in both breast cancers and GC/GEC [16]. Trastuzumab was the first HER2-targeted agent which demonstrated significant clinical activity in the advanced GC and GEC settings [26]. In the ToGA trial, addition of trastuzumab to chemotherapy increased the overall survival from 11.1 to 13.8 months (HR = 0.74, 95% CI = 0.60–0.91; p = 0.0046). There was also a significant improvement in progression-free survival and response rate with trastuzumab [12]. Unlike trastuzumab, no benefit in terms of overall survival (OS) was evident when bevacizumab was added to a combination of cisplatin and fluoropyrimidine in patients with GC/GEC [27]. Likewise, cetuximab therapy in combination with capecitabine and cisplatin did not achieve the primary endpoint with a median progression-free survival (PFS) of 4.4 months compared to 5.6 months in patients who received capecitabine-cisplatin alone [28]. The REAL-3 study which involved treatment with modified epirubicin/oxaliplatin/capecitabine (EOC) and panitumumab was terminated prematurely because the patients with advanced esophagogastric adenocarcinoma had a statistically significant lower OS [29]. The combination of fluoropyrimidine and platinum-containing chemotherapy, with the addition of trastuzumab remains the standard of care in HER2 positive populations [26]. The introduction of trastuzumab has opened up avenues for the development of anti-HER2 drugs that may be useful in the treatment of HER2-positive gastric cancer [7].

The Malaysian Cancer Statistics 2007 reported a total of 630 GC cases nationwide. A sample size of 228 in our study would therefore represent approximately one third of the population. Hence, the sample size used in our study can be considered an acceptable representation of the Malaysian population with GC/GEC.