mucosa: Innermost layer where the stomach acid and digestive juices are made.
Submucos: Supporting layer surrounded by the
muscularis: A layer of muscle that moves and mixes the stomach contents.
subserosa and serosa: (the outermost layer) act as wrapping for the stomach.

Most of the time stomach cancer starts in the mucosa. It can spread in different ways.

• grow through the wall of the stomach and into nearby organs.
• spread into the lymph system through the lymph nodes – small bean-sized structures that help fight infections.
• travel through the bloodstream and form deposits of cancer cells in organs such as the liver, lungs, and bones (advanced stage).

Most cancers of the stomach are of a type called adenocarcinomas. This cancer develops from cells that form the lining of the innermost layer, the mucosa. The term “stomach cancer” almost always refers to this type of cancer. Lymphomas, gastric stromal tumors, and carcinoid tumors are other, much less common, tumors that are found in the stomach.

Staging is the process of finding out by looking at the tumor and how far the cancer has spread. The treatment and the outlook for a patient’s recovery depend on the stage of the cancer.

After stage 0 (cancer that has not grown beyond the layer of cells that line the stomach), stages are labeled using Roman numerals I through IV (1-4). The lower the number, the less the cancer has spread. A higher number, such as stage IV (4), means a more serious cancer.

The two main ways of staging cancers are the TNM system and the number system.

1. TNM stages of stomach cancer
   'TNM' stands for Tumour, Node, Metastasis. The system can describe the size of a primary tumour, whether there are lymph nodes with cancer cells in them and whether the cancer has spread to a different part of the body.

   There are 4 stages of tumour size in stomach cancer:

   • T1 means the tumour has grown no further than the inner layer of the stomach
   • T2 means the tumour has grown into the muscle layer of the stomach wall
   • T3 means the tumour has broken through the membrane covering the outside of the stomach
   • T4 means the tumour has grown into other organs or body structures nearby such as the liver, gullet or abdominal wall

   There are 3 possible stages of lymph node involvement:

   • N0 means there are no lymph nodes containing cancer cells
   • N1 means there are cancer cells in lymph nodes that are less than 3.0 centimetres away from the main tumour in the stomach
   • N2 means there are cancer cells in lymph nodes that are further than 3cm away from the main tumour in the stomach OR in lymph nodes that are connected to the main blood vessels around the stomach

   There are two stages of metastasis:

   • M0 means there is no cancer spread to other organs
   • M1 means the cancer has spread to other parts of the body
2. Number stages of stomach cancer
   A simplified approach puts patients into six groups or stages based on how far the cancer has advanced:

   Stage 0	Cancer has just begun to affect the inner stomach. Very early stage of stomach cancer. very little risk of any cancer cells having spread. It is not usual for stomach cancer to be diagnosed this early.
   Stage I	Cancer has begun to penetrate toward the outer layer of stomach. Nearby lymph nodes may be involved. Earliest stage of cancer. It is divided into 1a and 1b. Stage 1a means the cancer has grown no further than through the inner lining of the stomach, with no cancer in the lymph nodes (T1, N0, M0). Stage 1b means either that The cancer has still only just grown through the lining, but nearby lymph nodes contain cancer cells (T1, N1, M0) OR There are no cancer cells in the lymph nodes, but the cancer has grown into the muscle of the stomach wall (T2, N0, M0).
   Stage II	Cancer has progressed farther through tissue layers of stomach and nearby lymph nodes are affected (T2, N1, M0).
   Stage III	Cancer has penetrated all tissue layers of stomach or distant lymph nodes may be involved. Stage 3 is also divided into a and b. Stage 3a means that The cancer has grown into the muscle layer, but lymph nodes further than 3cm away contain cancer cells (T2, N2, M0) OR The cancer has grown through the stomach wall, but only nearby lymph nodes contain cancer cells (T3, N1, M0) OR The cancer has grown right through the wall and into nearby tissues but no lymph nodes contain cancer cells (T4, N0, M0) In stage 3b, the lymph nodes are always affected. Either The cancer has grown just through the stomach wall and lymph nodes further than 3cm away contain cancer cells (T3, N2, M0) OR The cancer has grown through the stomach wall into surrounding body tissues and nearby lymph nodes contain cancer cells (T4, N1, M0)
   Stage IV	Cancer has affected nearby organs and tissues. This is known as metastasis. Grown through the stomach wall into body tissues next to the stomach and lymph nodes further than 3cm away contain cancer cells (T4, N2, M0) OR Spread to other body organs through the lymphatic system or bloodstream (any T or N, M1)