Quantitative proteomic analysis of HER2 expression in the selection of gastric cancer patients for trastuzumab treatment

Abstract

BackgroundA wide range of response rates have been reported in HER2-positive gastric cancer (GC) patients treated with trastuzumab. Other HER2-targeted therapies for GC have yet to show efficacy in clinical trials. These findings raise question about the ability of standard HER2 diagnostics to accurately distinguish between GC patients who would and would not benefit from anti-HER2 therapies.Patients and methodsGC patients (n = 237), including a subset from the Trastuzumab in GC (ToGA) trial were divided into three groups based on HER2 status and history of treatment with standard chemotherapy or chemotherapy plus trastuzumab. We applied mass spectrometry-based proteomic analysis to quantify HER2 protein expression in formalin-fixed tumor samples. Using HER2 expression as a continuous variable, we defined a predictive protein level cutoff to identify which patients would benefit from trastuzumab. We compared quantitated protein level with clinical outcome and HER2 status as determined by conventional HER2 diagnostics.ResultsQuantitative proteomics detected a 115-fold range of HER2 protein expression among patients diagnosed as HER2 positive by standard methods. A protein level of 1825 amol/µg was predicted to determine benefit from the addition of trastuzumab to chemotherapy. Trastuzumab treated patients with HER2 protein levels above this cutoff had twice the median overall survival (OS) of their counterparts below the cutoff (35.0 versus 17.5 months, P = 0.011). Conversely, trastuzumab-treated patients with HER2 levels below the cutoff had outcomes similar to HER2-positive patients treated with chemotherapy. (Progression-free survival = 7.0 versus 6.5 months: P = 0.504; OS = 17.5 versus 12.6 months: P = 0.520). HER2 levels were not prognostic for response to chemotherapy.ConclusionsProteomic analysis of HER2 expression demonstrated a quantitative cutoff that improves selection of GC patients for trastuzumab as compared with current diagnostic methods.

MET tyrosine kinase receptor expression and amplification as prognostic biomarkers of survival in gastroesophageal adenocarcinoma

“…26,37,38 In summary, MET FISH and Met SRM were independently associated with a poor prognosis in this large cohort of GEC patients, whereas Met IHC at the currently applied positivity cutoffs was not independently associated with outcomes. SRM is a novel technology demonstrating clinical utility with Met and Her2 11,27,39,45 and additionally has the advantage of multiplex peptide analysis, 22 which is analogous to nextgeneration sequencing for genomic aberrations. The results of this study suggest that amplification by FISH and/or overexpression by SRM should be incorporated into multivariate models when one is assessing the prognostic significance of other novel covariates.…”

Exceptional responses to pertuzumab, trastuzumab, and docetaxel in human epidermal growth factor receptor‐2 high expressing salivary duct carcinomas

“…23 This dichotomous approach inevitably leaves some patients in the gray area (equivocal) and some have discordant results of these 2 assays. 25,26 Both of our exceptional responders had high levels of HER2 protein in their tumors measured by a clinical quantitative proteomics assay, demonstrating a potential as an alternative assay in predicting the benefit of HER2 therapy, which could be replacing or complementing current methods. Previous research has shown that FIGURE 3 Human epidermal growth factor receptor-2 (HER2) expression level in salivary duct carcinomas using clinical proteomics.…”

“…Previous research has shown that FIGURE 3 Human epidermal growth factor receptor-2 (HER2) expression level in salivary duct carcinomas using clinical proteomics. 24,25 Although proteomic expression of HER2 in the nonresponder is above these cutoffs, it is at the low end of the range of expression correlated with benefit. 18 The HER2 expression level in tumors are calculated from the ratio of area under the curve for the endogenous transition ions for HER2 peptide A, C, and E, and isotopically labeled internal standard peptide B, D, and F, multiplied by the known amount of standard peptides spiked into the samples.…”

Salivary duct carcinoma: An aggressive salivary gland malignancy with opportunities for targeted therapy

“…Furthermore, many patients have tumors that are not strongly positive for ErbB2. In breast cancers and gastric cancers, level of Erb2 measured by quantitative proteomic assay was shown to correlate with response to Erb2 targeting therapy [77, 78]. Further investigations are needed to clarify whether Erb2 level can serve as a predictive biomarker.…”