HER2 Expression, Test Deviations, and Their Impact on Survival in Metastatic Gastric Cancer: Results From the Prospective Multicenter VARIANZ Study

Abstract

Purpose: Trastuzumab is the only approved targeted drug for first-line treatment of human epidermal growth factor receptor 2-positive (HER2+) metastatic gastric cancer (mGC). However, not all patients respond and most eventually progress. The multicenter VARIANZ study aimed to investigate the background of response and resistance to trastuzumab in mGC.

Methods: Patients receiving medical treatment for mGC were prospectively recruited in 35 German sites and followed for up to 48 months. HER2 status was assessed centrally by immunohistochemistry and chromogenic in situ hybridization. In addition, HER2 gene expression was assessed using qPCR.

Results: Five hundred forty-eight patients were enrolled, and 77 had HER2+ mGC by central assessment (14.1%). A high deviation rate of 22.7% between central and local test results was seen. Patients who received trastuzumab for centrally confirmed HER2+ mGC (central HER2+/local HER2+) lived significantly longer as compared with patients who received trastuzumab for local HER2+ but central HER2- mGC (20.5 months, n = 60 v 10.9 months, n = 65; hazard ratio, 0.42; 95% CI, 8.2 to 14.4; P < .001). In the centrally confirmed cohort, significantly more tumor cells stained HER2+ than in the unconfirmed cohort, and the HER2 amplification ratio was significantly higher. A minimum of 40% HER2+ tumor cells and a HER2 amplification ratio of ≥ 3.0 were calculated as optimized thresholds for predicting benefit from trastuzumab.

Conclusion: Significant discrepancies in HER2 assessment of mGC were found in tumor specimens with intermediate HER2 expression. Borderline HER2 positivity and heterogeneity of HER2 expression should be considered as resistance factors for HER2-targeting treatment of mGC. HER2 thresholds should be reconsidered. Detailed reports with quantification of HER2 expression and amplification levels may improve selection of patients for HER2-directed treatment.

Trial registration: ClinicalTrials.gov NCT02305043.

Conflict of interest statement

Birgitta GeierOther Relationship: Biomax Informatics AG Dieter MaierOther Relationship: Biomax Informatics AG Albrecht KretzschmarHonoraria: Roche Pharma AG, Merck Serono, Shire, Amgen, Medac, SERVIER, Sanofi, MSD, Bristol-Myers Squibb, Bayer Schering Pharma, Aspen PharmaConsulting or Advisory Role: Roche Pharma AG, Shire, AmgenTravel, Accommodations, Expenses: PharmaMar, Merck Serono, Ipsen, Medac Ludwig Von WeikersthalHonoraria: Novartis, Roche Pharma AG, AstraZeneca, Pierre Fabre Gabriele SieglerHonoraria: Medizinwelten services GmbH, Shire, Eisai, Roche, Janssen-Cilag, Aurikamed, Deutsche RöntgengesellschaftConsulting or Advisory Role: Janssen-Cilag, AstraZenecaResearch Funding: Servier, Beigene, Roche/Genentech, Roche, Celgene, Isofol Medical, Nutricia, Novartis, MOLOGEN, SanofiTravel, Accommodations, Expenses: Lilly Thomas DeckerConsulting or Advisory Role: Novartis Florian LordickHonoraria: Lilly, Merck Sharp & Dohme, Bristol-Myers Squibb, AstraZeneca, Elsevier, BioNTech AG, SERVIER, Infomedica, Merck KGaA, Roche, MedscapeConsulting or Advisory Role: Lilly, Merck Sharp and Dohme, Bristol-Myers Squibb, Astellas Pharma, SERVIER, Zymeworks, Amgen, BeigeneResearch Funding: Bristol-Myers SquibbTravel, Accommodations, Expenses: Bristol-Myers Squibb, LillyNo other potential conflicts of interest were reported.

Figures

FIG 1.

CONSORT diagram of the VARIANZ study. Patients were assigned to groups according to central HER2 test results, confirmation of local HER2 status, and treatment with trastuzumab. CUP, carcinoma of unknown primary; HER2, human epidermal growth factor receptor 2; Ltf, lost to follow-up; SCC, squamous cell carcinoma.

FIG 2.

Detailed central HER2 test results: number of tumor cells staining HER2+ by immunohistochemistry (A), amplification ratio for HER2/CEP17 by chromogenic in situ hybridization (B), and HER2 gene expression (∆Ct) (C) according to central HER2 status, central confirmation of HER2 status, and treatment with trastuzumab. Significant differences between the patient groups are calculated using the one-way analysis of variance test. Thresholds displayed are used in routine HER2 assessment or are calculated as optimized thresholds, best separating overall survival (Fig 4) of patients treated with trastuzumab. Significance is shown for *.01 < P ≤ .05, **.001 < P ≤ .01, and ***P ≤ .001. HER2, human epidermal growth factor receptor 2; HER2−, HER2-negative; HER2+, HER2-positive.

FIG 3.

OS of patients according to central HER2 status (HER2+ [green], HER2− [blue]) and central confirmation of HER2 status (green and blue represent confirmed HER2 status, and red represents deviating HER2 status). aTreatment with trastuzumab. HER2, human epidermal growth factor receptor 2; HER2−, HER2-negative; HER2+, HER2-positive. OS, overall survival.

FIG 4.

Calculation of optimized thresholds best separating OS of patients treated with trastuzumab. (A) Number of tumor cells staining HER2+ by immunohistochemistry, (B) amplification ratio for HER2/CEP17 by chromogenic in situ hybridization, and (C) HER2 gene expression (∆Ct). HER2, human epidermal growth factor receptor 2; HR, hazard ratio; OS, overall survival.

FIG A1.

HER2 staining examples in the VARIANZ study. (A) Example of intratumoral heterogeneity: unstained HER2 negative tumor cells on the left side, some normal stomach glands in the middle, and strongly staining HER2-positive tumor cells on the right side, (B) example of homogenously HER2-positive staining tumor cells. HER2, human epidermal growth factor receptor 2.