The system most often used to stage stomach cancer in the United States is the American Joint Commission on Cancer (AJCC) TNM system. The TNM system for staging contains 3 key pieces of information:

• T describes the extent of the primary tumor (how far it has grown into the wall of the stomach and into nearby organs).
• N describes the spread to nearby (regional) lymph nodes.
• M indicates whether the cancer has metastasized (spread) to other organs of the body. (The most common sites of distant spread of stomach cancer are the liver, the peritoneum (the lining of the space around the digestive organs), and distant lymph nodes. Less common sites of spread include the lungs and brain.)

Numbers or letters appear after T, N, and M to provide more details about each of these factors:

• The numbers 0 through 4 indicate increasing severity.
• The letter X means "cannot be assessed" because the information is not available. 
• The letters "is" mean "carcinoma in situ," which means the tumor is contained within the top layer of mucosa cells and has not yet invaded deeper layers of tissue.

T Categories of Stomach Cancer

The T category describes how far down through the stomach layers the cancer has invaded. To recall, the stomach is made of 5 layers. Starting from the inside and working our way out, the innermost layer is the mucosa. This is where stomach acid and digestive enzymes are made. Next is a supporting layer called the submucosa. This is surrounded by the muscularis, a layer of muscle that moves and mixes the stomach contents. The next 2 layers, the subserosa and the outermost serosa act as wrapping layers for the stomach.

• TX: The main tumor cannot be assessed
• T0: No evidence of a main tumor 
•  Tis (carcinoma in situ): Cancer cells are limited to the mucosa (innermost layer of the stomach) and have not invaded deeper layers of the stomach 
• T1: Tumor invades below the mucosa, into the connective tissue (lamina propria) or submucosa 
• T2: Tumor invades the muscularis (T2a) or tumor invades the subserosa (T2b) 
• T3: Tumor invades the serosa, but doesn't invade any nearby organ 
• T4: Tumor goes through the serosa and invades a nearby organ (spleen, intestines, pancreas, kidney, etc.) or other structures such as major blood vessels

N Categories of Stomach Cancer

• NX: Regional lymph nodes cannot be assessed 
• N0: No spread to nearby (regional) lymph nodes 
• N1: The cancer has spread to 1 to 6 nearby lymph nodes 
• N2: The cancer has spread to 7 to 15 nearby lymph nodes 
• N3: The cancer has spread to more than 15 nearby lymph nodes

M Categories of Stomach Cancer 

• MX: Spread to distant organs cannot be assessed 
• M0: No distant metastasis  
• M1: Distant metastasis (spread of the cancer to tissues or organs far away from the stomach) 

TNM Stage Grouping

The T, N, and M categories are combined and expressed as a stage, using Roman numerals I through IV. This is known as stage grouping.

Stage 0: Tis, N0, M0: This is cancer in its earliest stage. It has not grown beyond the inner layer of cells that line the stomach. This stage is also known as carcinoma in situ.

Stage IA: T1, N0, M0: The cancer has invaded beneath the mucosa into the connective tissue (lamina propria) or the submucosa. But it has not grown into the main muscle layer of the stomach, called the muscularis. The cancer has not spread to any lymph nodes or anywhere else.

Stage IB: Two combinations of T and N features are assigned to this stage.

• T1, N1, M0: Just as in stage IA, the cancer has grown into the connective tissue (lamina propria) or submucosa but it has not grown into the muscularis, the main muscle layer of the stomach. It has also spread to as many as 6 lymph nodes near the stomach, but not to any other tissues or organs. 
• T2a/b, N0, M0: The cancer has grown into the main muscle layer of the stomach wall, called the muscularis, and may have grown into the subserosa. It has not spread to any other tissues or organs and has not spread to any lymph nodes.

Stage II: Three combinations of T and N features are assigned to this stage.

• T1, N2, M0: The cancer has invaded beneath the mucosa into the connective tissue (lamina propria) or the submucosa. It has not grown into the main muscle layer, but it has spread to between 7 and 15 lymph nodes near the stomach. 
• T2a/b, N1, M0: The cancer has grown into the main muscle layer and may have grown into the subserosa. It has not spread to any nearby tissues or organs, but it has spread to 1 to 6 lymph nodes near the stomach. 
• T3, N0, M0: The cancer has grown through all the layers to the outside the stomach. It has not spread to any nearby tissues or organs and it has not spread to any lymph nodes.

Stage IIIA: Three combinations of T and N features are assigned to this stage.

• T2a/b, N2, M0: The cancer has grown into the main muscle layer and may have spread into the subserosa. It has not spread to any nearby tissues or organs, but it has spread to between 7 and 15 lymph nodes near the stomach. 
• T3, N1, M0: The cancer has grown completely through all the layers to the outside of the stomach. It has not spread to any nearby tissues or organs, but it has spread to between 1 and 6 lymph nodes near the stomach. 
• T4, N0, M0: The cancer has grown completely through the stomach wall and into other nearby organs, such as the spleen, intestines, kidneys, or pancreas. It has not spread to any lymph nodes.

Stage IIIB: T3, N2, M0: The cancer has grown completely through all the layers to the outside of the stomach. It has not spread to any nearby tissues or organs, but it has spread to between 7 and 15 lymph nodes near the stomach.

Stage IV: Three combinations of T, N, and M features are assigned to this stage.

• T4, N1-3, M0: The cancer has grown completely through the stomach wall into other nearby organs, such as the spleen, liver, intestines, kidneys, or pancreas. It has also spread to nearby lymph nodes, but it has not spread to distant organs. 
• T1-3, N3, M0: The cancer has spread to more than 15 lymph nodes, but it has not spread to distant organs. 
• Any T, any N, M1: The cancer has spread to distant organs such as the liver, lungs, brain, or bones.

If you have any questions about the stage of your disease, ask your doctor to explain this to you. The stage of a stomach cancer is an important factor, but it is not the only factor in considering treatment options and in predicting outlook for survival.

Five-Year Survival Statistics by Stage

The 5-year survival rate refers to the percentage of patients who live at least 5 years after their cancer is diagnosed. Of course, some people live much longer than 5 years. Five-year rates are used as a standard way of discussing prognosis. The 5-year relative survival rate compares the observed survival of people with stomach cancer to that expected for people without stomach cancer. Therefore, relative survival mainly talks about deaths from stomach cancer; it tries to exclude people with stomach cancer who might die from other causes. This is thought to be a more accurate way to describe the outlook for patients with a certain type and stage of cancer.

The overall 5-year relative survival rate of all people with stomach cancer in the United States is about 24%. This survival rate has improved only slightly in the last 20 years. One reason for this is that most stomach cancers in the United States are diagnosed at an advanced rather than an early stage. The stage (extent) of the cancer has a major effect on a patient's prognosis (outlook for survival).

Another important factor is the location of the cancer. The 5-year survival rate for cancers of the distal stomach (the lower portion of the stomach) is higher than for cancers in the proximal stomach (the upper portion of the stomach). It is important to remember that statistics on cancer survival are averages. The outlook for any individual patient can't be predicted with certainty, and many people survive much longer than would be expected based on the stage of their cancer.

The 5-year relative survival rates for stomach cancer by stage are as follows:

Stage 0:	77%
Stage IA:	66%
Stage IB:	57%
Stage II:	35%
Stage IIIA:	17%
Stage IIIB:	12%
Stage IV:	3%

These numbers come from the American College of Surgeons National Cancer Data Base and refer to more than 11,000 patients who were treated in 1998. Because these numbers are several years old, outcomes for people diagnosed with stomach cancer today may be better.