This map explains stomach cancer step by step: what it is, the types, the tests, the stages, the treatment and its side effects.
Tap any topic on the map to read about it. Topics with an arrow open more topics.
Most stomach cancers are adenocarcinoma. Tests on the biopsy (markers) are now as important as the type. Tap a topic on the map.
| Marker | What it can mean |
|---|---|
| HER2 | If positive, trastuzumab (and later trastuzumab deruxtecan) is added. |
| PD-L1 (CPS score) | A higher score means immunotherapy is more likely to help. |
| MMR / MSI | dMMR / MSI-high cancers respond very well to immunotherapy. |
| Claudin 18.2 | If positive, zolbetuximab can be added to chemotherapy. |
Why this matters: in stage 4 stomach cancer, these markers decide which medicine is added to chemotherapy.
GIST (gastrointestinal stromal tumour), lymphoma and neuroendocrine tumours can also start in the stomach. They are treated very differently and are not covered on this map: GIST · Lymphoma · Neuroendocrine tumours
Tap a test on the map to see why it is done.
Please wait for all the reports. Why we wait
A camera passed through the mouth to see the stomach and take biopsies. The biopsy confirms the cancer and is used for the marker tests.
CT scan of the chest, abdomen and pelvis checks for spread. PET-CT is used in some patients. Small deposits in the peritoneum are often not seen on scans.
A keyhole look inside the abdomen, under anaesthesia, before major surgery. It finds small deposits on the peritoneum that scans miss, so that a large operation is not done when it cannot help.
Before starting chemotherapy, immunotherapy or targeted therapy, these tests check that you are fit for treatment, and give a starting point to compare with later.
| Test | Why it is done |
|---|---|
| CBC (complete blood count) | Haemoglobin, white cells and platelets. Treatment can lower them. |
| RFT (kidney function) | Many medicines are cleared by the kidneys; the dose may need to change. |
| LFT (liver function) | Many medicines are processed by the liver. |
| Viral markers: HBsAg, anti-HCV, HIV | Hepatitis B can flare up during treatment. If positive, a tablet is given to prevent this. |
| Blood sugar (and HbA1c if diabetic) | Steroids given with chemotherapy can raise blood sugar. |
| ECG and 2D Echo | Check the heart rhythm and pumping before treatment, as some medicines affect the heart. |
Before immunotherapy, also:
| Test | Why it is done |
|---|---|
| Serum TSH (thyroid) | Immunotherapy can affect the thyroid gland. |
| Serum cortisol (morning sample) | Immunotherapy can affect the adrenal and pituitary glands. |
Sometimes needed, depending on your treatment:
Your doctor will choose the tests that apply to you. Some of them are repeated during treatment.
The stage tells how far the cancer has spread. Tap your stage on the map.
Limited to the inner layers of the stomach wall, with no or very few lymph nodes. Early; the aim is cure.
Grown deeper into or through the stomach wall, and/or spread to nearby lymph nodes. Locally advanced; the aim is cure.
Spread to other organs or the peritoneum. Usually not curable, but treatment can control it and relieve symptoms.
Treatment depends on the stage and markers. Tap your stage on the map.
Side effects: surgery
Side effects: chemotherapy · immunotherapy · surgery
Side effects: chemotherapy · immunotherapy · targeted medicines
Tap a treatment on the map. Most side effects can be prevented or managed.
Vomiting blood, black stools, repeated vomiting with inability to eat or drink, severe tummy pain, or fever of 38°C or more need urgent care.
This information is general. Your own treatment plan may be different. Please discuss it with your doctor.
Written and medically reviewed by Dr Prathyusha Eaga, MD, DM (Medical Oncology). Last reviewed: 12 October 2026. Based on NCCN and ESMO guidelines.
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