22 Sep Evaluating Clinical Evidence and Patient Selection in First-Line HER2+ GEA Treatment
First-line treatment options for HER2-positive gastroesophageal adenocarcinoma (GEA) are rapidly evolving with new clinical evidence emerging to compare targeted therapies, chemotherapy, and immunotherapy across various patient populations. Given that a HER2-positive metastatic GEA designation does not by itself determine the appropriate first-line treatment for individual patients, a review of key clinical trials, biomarkers for molecularly targeted agents, disease-related characteristics, and patient-related factors is essential to help healthcare professionals evaluate available evidence and select optimal first-line regimens. According to the NCI (National Cancer Institute), HER2-positive gastric and gastroesophageal junction adenocarcinomas represent a distinct molecular subset for which targeted therapy has significantly changed the treatment landscape over the past decade, with ongoing clinical trials continuing to refine optimal combinations and sequencing strategies.
Establishing HER2-Positive Disease
Most adenocarcinomas of the stomach and gastroesophageal junction are HER2 negative, but a subset of gastric cancers overexpress the HER2 protein or have amplification of the HER2 gene. It is therefore very important that HER2 testing is performed on all tumor specimens from patients with gastric or gastroesophageal junction adenocarcinomas, and that results are interpreted by an experienced pathologist. Typically, HER2 expression is measured using immunohistochemistry (IHC) and HER2 gene amplification is detected using in situ hybridization (ISH). In some instances, cases can be tested using both methods and results correlated. Understanding the criteria for testing and accurately reporting results are critical for determining eligibility for anti-HER2 treatment. Pathological specimens must be of sufficient quality to support a diagnostic decision; ideally the tumor specimen would be representative of the whole tumor.
Understanding the Clinical Evidence
The clinical evidence for gastric cancer must be evaluated within the boundaries of the specific clinical study, including the study design, patient population, biomarker definitions and required values, treatments, comparators, endpoints, and follow-up durations. Clinical evidence has shown that in addition to trastuzumab in conjunction with chemotherapy as first-line treatment for patients with advanced or metastatic HER2-positive GEA, the incorporation of immune checkpoint inhibitors to chemotherapy plus trastuzumab has become another approach for this patient population. Pembrolizumab has been evaluated in combination with trastuzumab and fluoropyrimidine- and platinum-containing chemotherapy for locally advanced unresectable or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma in patients whose tumors express PD-L1 with a combined positive score (CPS) of 1 or greater. In August 2026, zanidatamab-hrii was approved for use in combination with chemotherapy and tislelizumab-jsgr for patients with HER2-positive gastric, gastroesophageal junction, or esophageal adenocarcinoma.
Evaluating Biomarker Profiles
Molecular markers such as PD-L1 are not evaluated in isolation from other molecular markers, and their clinical significance can vary greatly depending on the indication for the HER2-directed treatment under evaluation. The combined positive score (CPS) for assessment of PD-L1 expression is the same for gastric and GEJ adenocarcinomas and only needs to be considered in the context of treatments for which evidence exists for use of immune checkpoint inhibitors. Some cancers have additional biomarkers that can be important in choosing a treatment. For example, if a cancer has been tested for mismatch repair (MMR) status or microsatellite instability (MSI) status, this can help identify other treatments or clinical trials that may be of use to the patient. The ultimate goal is to gain enough molecular information to make a treatment decision — a single biomarker is not sufficient on its own.
Assessing Patient Eligibility
After molecular characterization of the tumor, consideration must be given to the clinical characterization of the patient to assess candidacy for a given treatment regimen. Many of the same considerations that influence chemotherapy decisions can influence decisions about targeted or combination therapies. These factors include patient performance status, age, comorbid diseases, organ function, nutrition, extent of disease, symptoms, and prior treatment. Whether a patient has a low volume of tumor and good functional status, or is experiencing rapid deterioration of symptoms — such as abdominal obstruction or bleeding — would influence whether a more aggressive or a palliative approach would be chosen. The preferences of the patient and their treatment goals should also be considered when selecting the appropriate systemic treatment.
Balancing Efficacy and Safety
When evaluating potential treatments for a patient with cancer, a healthcare professional must consider both the potential benefits and the potential for toxic effects with each treatment option. Even a treatment considered particularly effective for patients with HER2-positive cancers — such as trastuzumab-based treatments — can have specific adverse effects, including potential cardiac effects. Side effects for immune checkpoint inhibitors can include immune-mediated toxicities that are organ-specific, affecting the lung, liver, gastrointestinal tract, skin, and endocrine organs. The side effect profile of a combination regimen must be assessed prior to treatment and monitored throughout. The potential treatment benefits must be weighed against the potential for significant adverse effects and impact on the patient’s quality of life.
Interpreting Evidence for Newer Therapies
Many newer agents have also been shown to be active in patients with cancers that express HER2 proteins. However, careful interpretation of the available evidence regarding their use is critical. The results of a study of a novel single agent, or combination of agents, may be of particular interest to patients in later lines of therapy and/or different tumor types, biomarker-defined populations, and/or different treatment combinations. When assessing evidence for newer HER2-targeted therapies, it is critical to interpret the evidence in the context in which the trial was conducted — including patient population, treatment line, tumor type, and biomarker status. Whether the agent has received FDA approval and for what specific indication must also be taken into account when assessing whether the results of a clinical study can be generalized to a specific patient.
The Role of Multidisciplinary Decision-Making
Different disciplines must be involved in the selection of the appropriate treatment. Pathologists correctly interpret the biomarkers. Radiologists assess the extent of disease and the response to treatment. Medical oncologists integrate clinical and molecular information to choose the appropriate systemic treatment. Pharmacists monitor for drug interactions and administration issues. Nursing staff provide the patient with education and serve as a resource to the oncologist and patient as they monitor for signs of toxicity. Multidisciplinary conversation during first-line treatment for HER2-positive GEA is essential to better understand the disease and the patient under discussion.
Monitoring Clinical Benefit
Selecting first-line HER2+ GEA treatment is not a one-time decision. There is a continuing need to follow patients on treatment and monitor for evidence of clinical benefit or increased toxicity, changes in functional status, and other evolving treatment goals. Imaging assessments of tumor response provide objective information regarding clinical benefit. Assessment of symptoms and clinical status also provide important information regarding whether patients are deriving benefit from their treatment. If disease progresses or side effects become too intense, the treatment options can be reassessed by the multidisciplinary team and an alternative therapy chosen.
Looking Ahead
In the future, patient selection for treatment of HER2-positive GEA is predicted to become increasingly individualized, considering a variety of factors including the tumor’s molecular characteristics, the patient’s general health and clinical condition, and patient preferences. Most importantly, healthcare professionals need to understand the distinction between evidence-based treatment options and those still under investigation, test for the appropriate biomarkers to confirm eligibility for specific treatments, and regularly assess both the benefit and tolerance of treatment options. Combining clinical evidence with individualized patient assessment may assist the oncology team in developing the appropriate first-line GEA treatment strategy for each patient’s specific situation, ensuring safe use and preserving all subsequent therapeutic options.
For a broader overview of how HER2 testing, immune checkpoint inhibitor combinations, and biomarker-guided treatment selection are evolving in gastroesophageal cancer, see this MedicalResearch.com overview of HER2-positive gastric cancer treatment — what the evidence shows.
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Last Updated on September 22, 2026 by Marie Benz MD FAAD