Stomach cancer is classified into five main stages, numbered 0 through IV, based on how deeply the tumor has grown into the stomach wall, whether it has reached nearby lymph nodes, and whether it has spread to distant organs. Each stage carries a significantly different outlook: the five-year survival rate ranges from about 78% when the cancer is still confined to the stomach down to roughly 8% once it has spread to distant sites.
How the Stomach Wall Determines Your Stage
The stomach wall has several distinct layers, and staging hinges on which layers the cancer has penetrated. From innermost to outermost, these are the mucosa (the inner lining), the submucosa (a supportive tissue layer beneath it), the muscle layer, the subserosa, and the serosa (the outermost covering). A tumor that stays in the mucosa is far easier to treat than one that has punched through to the outer surface of the stomach or beyond.
Staging also counts how many nearby lymph nodes contain cancer cells. The ranges matter: 1 to 2 positive nodes, 3 to 6, 7 to 15, and 16 or more each push the cancer into a higher category. For accurate staging, surgeons typically need to remove and examine at least 16 lymph nodes during an operation.
Stage 0: Abnormal Cells in the Lining
Stage 0 is sometimes called “carcinoma in situ.” Cancer cells are present only in the innermost surface of the mucosa and have not grown into deeper layers. At this point there is no lymph node involvement and no spread elsewhere. Stage 0 can sometimes be treated without traditional surgery, using an endoscopic procedure that removes the abnormal tissue through a flexible tube passed down the throat.
Stage I: Cancer Still Close to the Surface
In stage I, the tumor has grown from the mucosa into the submucosa or, at most, into the muscle layer. Lymph node involvement is absent or minimal, limited to one or two nearby nodes at most. This is still considered early-stage disease, and the primary treatment is surgical removal of part or all of the stomach along with surrounding lymph nodes. Some patients with node-positive or muscle-invasive tumors also receive chemotherapy or a combination of chemotherapy and radiation after surgery.
Early stomach cancer often produces vague symptoms or none at all, which is one reason it’s frequently diagnosed at later stages in Western countries. When symptoms do appear, they tend to be easily mistaken for indigestion or heartburn.
Stage II: Deeper Growth or More Lymph Nodes
Stage II is split into IIA and IIB, reflecting different combinations of tumor depth and lymph node spread.
In stage IIA, the cancer may have reached the submucosa with 3 to 6 positive lymph nodes, grown into the muscle layer with 1 to 2 positive nodes, or pushed into the subserosa without any lymph node involvement. In stage IIB, the combinations escalate: the tumor in the submucosa has reached 7 to 15 nodes, or it has penetrated the muscle layer with 3 to 6 nodes involved, or it has reached the subserosa with 1 to 2 nodes, or it has grown all the way through to the serosa (the outer surface) without node involvement.
Treatment for stage II typically involves surgery combined with chemotherapy given either before and after the operation (perioperative chemotherapy) or after surgery alongside radiation. The goal is to eliminate cancer cells that may have escaped the primary tumor.
Stage III: Extensive Local or Regional Disease
Stage III represents a wide spectrum of disease, divided into substages IIIA, IIIB, and IIIC. What they share is that the cancer has either grown deeply into or through the stomach wall, spread to many lymph nodes, or both.
In stage IIIA, possibilities include cancer in the muscle layer with 7 to 15 positive nodes, cancer in the subserosa with 3 to 6 nodes, cancer reaching the serosa with up to 6 nodes, or cancer that has grown into a neighboring organ (such as the spleen, liver, colon, or pancreas) without lymph node spread. Stage IIIB raises the stakes further: tumors in the submucosa or muscle layer with 16 or more positive nodes, cancer in the subserosa or serosa with 7 to 15 nodes, or cancer invading a nearby organ with up to 6 positive nodes. Stage IIIC involves the most extensive combinations, with cancer in the subserosa or serosa plus 16 or more nodes, or cancer in a nearby organ with 7 or more positive nodes.
Surgery is still part of the plan for many stage III patients, but it is almost always paired with chemotherapy before, after, or both before and after the operation. Some patients receive radiation as well. The treatment approach is typically decided by a team of specialists, because the extent of disease varies so much within this stage.
Stage IV: Cancer Has Spread to Distant Sites
Stage IV means the cancer has metastasized to organs or tissues far from the stomach. The most common destinations are the liver, the peritoneum (the tissue lining the abdominal cavity), the lungs, and distant lymph nodes. Regardless of tumor size or how many nearby nodes are involved, any distant spread automatically places the cancer at stage IV.
Symptoms at this stage tend to be more pronounced and vary depending on where the cancer has traveled. Liver spread can cause pain on the right side of the abdomen, jaundice, and fluid buildup. Cancer in the peritoneum often leads to significant abdominal swelling from fluid accumulation, along with appetite loss and nausea. Lung metastases may cause a persistent cough, shortness of breath, or recurrent chest infections. Unexplained weight loss, bloody or black stools, and persistent fatigue are common regardless of where the cancer has spread.
Treatment at stage IV focuses on controlling the disease and managing symptoms rather than curing it. Chemotherapy is the backbone, often combined with immunotherapy or targeted therapy depending on the tumor’s molecular profile. The five-year relative survival rate for distant stomach cancer is about 8%, though individual outcomes vary.
Biomarker Testing Shapes Treatment Decisions
Beyond the traditional staging system, doctors now test stomach cancer tumors for specific molecular characteristics that affect which treatments will work best. Three biomarkers are particularly important.
HER2 is a protein that, when overproduced by cancer cells, drives faster growth. About 10 to 20% of stomach cancers are HER2-positive, and these patients benefit from targeted drugs that block the protein. Guidelines recommend testing for HER2 in all patients with metastatic or suspected metastatic disease.
PD-L1 is a protein some tumors use to hide from the immune system. When a tumor scores high for PD-L1 expression, adding immunotherapy to chemotherapy significantly improves survival. In one major trial, combining an immune checkpoint inhibitor with chemotherapy reduced the risk of death by 29% compared to chemotherapy alone in patients with high PD-L1 scores.
A third marker, called microsatellite instability (MSI), reflects problems with the cell’s DNA repair machinery. Tumors with high microsatellite instability tend to respond especially well to immunotherapy, sometimes even without traditional chemotherapy.
How Staging Tests Work
Determining the exact stage requires a combination of procedures. An upper endoscopy lets doctors visually inspect the stomach lining and take tissue samples for biopsy. Endoscopic ultrasound is particularly useful for gauging how deep a tumor has grown into the stomach wall and whether nearby lymph nodes look abnormal.
CT scans provide a broader picture, showing the stomach, liver, lymph nodes, and other areas where cancer might have spread. PET scans look for cancer activity throughout the entire body at once and are helpful for spotting distant metastases that a CT might miss. MRI is used less often but can be valuable for evaluating suspicious spots in the liver.
If imaging suggests the cancer hasn’t spread but the stage is uncertain, doctors may perform a staging laparoscopy, a minimally invasive procedure where a small camera is inserted through the abdomen. This allows direct inspection of abdominal surfaces and lymph nodes and can detect small areas of spread that imaging tests sometimes miss.
Survival Rates by Stage
The National Cancer Institute’s SEER database groups survival data into three broad categories rather than individual stages. For cancers still confined to the stomach (localized), the five-year relative survival rate is 78.1%. Once cancer has reached regional lymph nodes, that drops to 39.0%. For distant disease, it falls to 8.1%.
These numbers represent averages across large populations and reflect cases diagnosed between 2016 and 2022. Individual prognosis depends on many factors, including the tumor’s molecular profile, how well it responds to treatment, the patient’s overall health, and which specific substage applies. Newer treatments, particularly immunotherapy combinations, have improved outcomes for some patients with advanced disease in recent years, and these gains may not yet be fully captured in the survival statistics.