IHC/FISH discrepancies were attributed to basolateral membranous immunoreactivity of glandular cells resulting in incomplete membranous reactivity and/or a higher rate of tumour heterogeneity in gastric cancer compared with breast cancer. With modifications to the IHC scoring system, the HercepTest is considered valid for the identification of HER2+ gastric tumours for this clinical trial. Correlation of HER2 scores with clinical outcomes will be needed to determine which patients might benefit from trastuzumab therapy.

BackgroundIn the Trastuzumab for GAstric cancer (ToGA) study, trastuzumab plus chemotherapy improved median overall survival by 2.7 months in patients with human epidermal growth factor receptor 2 (HER2)-positive [immunohistochemistry (IHC) 3+/fluorescence in situ hybridization-positive] gastric/gastroesophageal junction cancer compared with chemotherapy alone (hazard ratio 0.74). Post hoc exploratory analyses in patients expressing higher HER2 levels (IHC 2+/fluorescence in situ hybridization-positive or IHC 3+) demonstrated a 4.2-month improvement in median overall survival with trastuzumab (hazard ratio 0.65). The ToGA study provides the largest screening dataset available on HER2 overexpression/amplification in this indication. We further analyzed correlation(s) of HER2 overexpression/amplification with clinical and epidemiological factors.MethodsHER2-positivity was analyzed by histological subtype, tumor location, geographic region, and specimen type. Exploratory efficacy analyses were performed.ResultsThe HER2-positivity rate was 22.1 % across analyzed tumor samples. Rates were similar between European and Asian patients (23.6 % vs. 23.9 %), but higher in intestinal- vs. diffuse-type (31.8 % vs. 6.1 %), and gastroesophageal junction cancer versus gastric tumors (32.2 % vs. 21.4 %). Across all IHC scores, variability in HER2 staining (≤30 % stained cells) was observed in almost 50 % of cases, with increasing rates in lower IHC categories, and did not affect treatment outcome. The polysomy rate was 4 %.ConclusionsHER2 expression varies by tumor location and type. All patients with advanced gastric or gastroesophageal junction cancer should be tested for HER2 status, preferably using IHC initially. Due to the unique characteristics of gastric cancer, specific testing/scoring guidelines should be adhered to.Electronic supplementary materialThe online version of this article (doi:10.1007/s10120-014-0402-y) contains supplementary material, which is available to authorized users.

PurposeTo determine whether (1) immunohistochemical (IHC) HER2 status (ie, 2+ or 3+), (2) degree of fluorescence in situ hybridization (FISH) amplification according to (2a) HER2/CEP17 ratio or (2b) HER2 gene copy number, or (3) polysomy significantly influenced clinical outcome for patients with human epidermal growth factor receptor 2 (HER2) –positive breast cancer enrolled in the Herceptin Adjuvant trial of trastuzumab versus no trastuzumab administered after completion of chemotherapy.Patients and MethodsIHC and/or FISH analyses were performed locally and required central confirmation as indicating HER2 positivity for trial entry. FISH data from the central HER2 analysis on patients in the 1-year trastuzumab and no trastuzumab arms were assessed in relation to disease-free survival (DFS) after a median 2 years of follow-up.ResultsCentral FISH results were available for 2,071 (61%) of the 3,401 patients randomized to the 2 arms. Among patients with FISH-positive disease, (1) the hazard ratios for trastuzumab versus no trastuzumab were 0.56 (95% CI, 0.32 to 0.99) for locally IHC2+ cases (n = 340) and 0.80 (95% CI, 0.40 to 1.61) for centrally IHC2+ cases (n = 299). There was no significant prognostic relationship between (2a) HER2 FISH ratio, (2b) HER2 copy number, or (3) polysomy and DFS in the control arm or predictive relationship defining differential benefit from trastuzumab.ConclusionThere was no evidence for reduced benefit of trastuzumab in HER2 IHC2+FISH+ cases. The degree of HER2 amplification does not influence prognosis or benefit from adjuvant trastuzumab in patients treated with prior adjuvant chemotherapy.