HER2-positive gastric cancer: testing and treatment sequence

Understand the HER2 result before choosing a drug

HER2 is commonly assessed by immunohistochemistry, or IHC. A strongly positive result can establish HER2 positivity, while an intermediate result may need an amplification test such as in situ hybridization. Ask for the staining score and any confirmatory result.

Gastric tumors can have uneven HER2 expression, so the sample and interpretation matter. If the report is incomplete or the tissue limited, a pathology review may be useful. A breast cancer HER2 explanation should not automatically be applied to gastric cancer scoring and treatment.

Sources and references: [1]

Keep the focus on the setting that has evidence

HER2-directed treatment is particularly relevant to advanced or metastatic gastric and gastroesophageal junction adenocarcinoma. For a removable tumor, ask how the HER2 result fits the evidence for treatment before or after surgery; the sequence should be planned for that setting.

Ask how the HER2 finding changes your treatment at the current stage. If surgery remains feasible, the team should explain the whole perioperative strategy. If disease has spread, the discussion centers on a systemic combination and a clear schedule for assessing its effect.

Sources and references: [1]

What may be included in initial advanced-disease treatment

Trastuzumab can be combined with fluoropyrimidine-platinum chemotherapy for HER2-positive advanced disease. PD-L1 testing adds another decision: the US pembrolizumab combination with trastuzumab and chemotherapy requires CPS of at least 1 in its first-line advanced gastric or GEJ indication.

The team should identify which results support each component. Ask about cardiac assessment for HER2-directed treatment, baseline blood tests and the expected clinic schedule. For care in China, confirm the exact combination's local indication and practical availability before planning the treatment course.

Sources and references: [1] [2]

If the first regimen stops working

Progression calls for review of the scan pattern, previous benefit and current health. The team may discuss whether a new biopsy would clarify whether HER2 remains a useful target or whether other features now matter. A previous positive result should be interpreted in the context of treatment already received.

Ask which options remain if HER2-directed treatment is no longer appropriate. Chemotherapy-based alternatives, a matched trial and symptom-focused interventions may all deserve discussion. The aim is to choose a coherent next step rather than continue targeting HER2 simply because it appeared on the first report.

Sources and references: [1]

Where trastuzumab deruxtecan fits

Trastuzumab deruxtecan combines a HER2-directed antibody with a cytotoxic payload. Its US gastric cancer indication includes previously trastuzumab-treated, HER2-positive locally advanced or metastatic gastric or GEJ adenocarcinoma.

Ask why an antibody-drug conjugate fits now and how its expected benefit compares with the available non-HER2 alternatives. The treatment still requires blood tests and symptom monitoring. It is important to use the gastric cancer regimen and instructions specified by the prescriber, rather than borrowing a schedule used for another cancer.

Sources and references: [1]

New breathing symptoms need prompt assessment

Trastuzumab deruxtecan can cause interstitial lung disease or pneumonitis, which can be serious. Tell the treating team promptly about a new cough, breathlessness, fever or reduced exercise tolerance. Severe breathing difficulty warrants emergency assessment.

Blood-count suppression, nausea and other side effects also need a prevention and monitoring plan. Mention existing lung disease and previous chest radiation at the consultation. Ask who will assess new symptoms between infusions and how the team will distinguish treatment effects from infection or cancer-related problems.

Sources and references: [1]

Protect eating and daily function during the sequence

Treatment benefit is easier to use when symptoms are managed early. Report weight loss, difficulty swallowing, vomiting or early fullness. Ask for nutrition support and an explanation of whether a local procedure is needed for bleeding or obstruction.

Keep a record of how long you recover after each cycle and what activities become difficult. Dose adjustments and supportive medicines may help maintain treatment. When comparing options, include travel days, infusion time and the availability of urgent support near where you will stay.

Sources and references: [1] [3]

Arrange a HER2-focused review in Shanghai

The Fudan Cancer Center profile connects to a Shanghai gastric cancer resource. A focused inquiry should include HER2 IHC and amplification results, PD-L1 CPS and all previous systemic treatment.

EastMedGo can help organize these records and coordinate questions about the appropriate consultation. Use contact to tell us whether the concern is initial treatment or progression after trastuzumab. We can help clarify the receiving team's requirements, visit timing and charges while the medical team evaluates the sequence.

Sources and references: [4]

Common questions