Stomach cancer has four stages in the TNM system used by the American Joint Commission on Cancer. The TNM system uses three metrics: extent of the primary tumor, the degree of spread to lymph nodes, and metastasis elsewhere in the body, notes the American Cancer Society.
Almost all stomach cancers begin in the mucosa, or the inner layer of the stomach wall, according to the American Cancer Society. The T category indicates how far the cancer has moved through the five layers of the stomach. The mucosa itself has three parts, and the next layer is the submucosa. After that come the muscularis propria, which is the muscle that moves the stomach, mixing the contents inside, and then the subserosa and serosa, which combine to wrap the stomach.
Assessing the N factor requires analyzing nearby lymph nodes for the spread of cancer. This rating ranges between N0, no spread, to N3b, which indicates spreading to at least 16 lymph nodes near the stomach, states the American Cancer Society. Rating the M factor results in M0, indicating no spreading to distant places or organs such as the brain or lungs, or M1, meaning that it has spread to lymph nodes or organs distant from the stomach. Combining these three factors results in staging of the stomach cancer between Stage 0, in which the cancer is limited to the inner layer of the stomach with no presence in lymph nodes and no metastasis, and Stage IV, which shows metastasis, lymph node presence and tumor spread in the stomach.