Doctors use the TNM staging system for most types of cancer. The TNM system uses letters and numbers to describe the tumor (T), lymph nodes (N), whether or not the cancer has spread or metastases (M). Each letter and number tell you something about the cancer. The specific definitions for each category are different for each type of cancer that is staged using this system. Learn more specific staging information for each type of cancer. Tumor (T): The letter T and the number after it describe the tumor by answering these questions: How large is the primary tumor? Does it go into other tissues or organs in the same area? Where is it located? The letter T is followed by a letter, number, or combination of letters after it. This gives additional information about the tumor. The different letters and numbers that may see include: TX means that there is no information about the tumor or it cannot be measured. T0 means that there is no evidence of a tumor. Tis refers to a tumor "in situ." This means that the tumor is only found in the cells where it started. It has not spread to any surrounding tissue. T1-T4 describe the size and location of the tumor, on a scale of 1 to 4. A larger tumor or a tumor that has grown deeper into nearby tissue will get a higher number. For some types of cancer, the T stage can be broken down into subcategories for even more detail. This is noted with a lowercase letter, like an "a" or "b", such as "T2b". What these letters mean depends on the type of cancer. A lowercase "m" can also be used to show that there are multiple tumors. Node (N): The letter N and the number after it describe if cancer has affected the lymph nodes. The lymph nodes are small, bean-shaped organs that help fight infection. They are a common spot where cancer first spreads. This part of the staging system answers these questions: Has the tumor spread to the lymph nodes? If so, which lymph nodes and how many? Lymph nodes near where the cancer started are called regional lymph nodes. Lymph nodes in other parts of the body are called distant lymph nodes. The N category only refers to lymph nodes near the cancer (regional lymph nodes). Distant lymph nodes elsewhere in the body are included in the "M" category (see below). After the letter N, there will be a number from 0 (zero) to 3. N0 means there are no lymph nodes with cancer. Most often, the more lymph nodes with cancer, the larger the number. But for some tumors, the location of the lymph nodes with cancer may determine the "N" category. Metastasis (M): The letter M and the number after it describes if the cancer has spread. It answers these questions: Has the cancer spread to other parts of the body? If so, where and how much? If cancer has not spread, the stage is M0. If the cancer has spread to other parts of the body, it is stage M1.