• T0 means the tumor was completely removed by the biopsy used to establish the diagnosis. T1 indicates the
smallest tumor. T2, T3 and T4 indicate larger tumors that may have grown into surrounding tissues.
• N0 means that the nearby lymph nodes are free of tumor. N1, N2 and N3 signify increasing degrees of
involvement of these regional nodes. An N2 tumor is more serious than an N1 tumor.
• M0 means that no distant metastases (cancer cells) have been found. If there are metastases, the classification
is M1.
This seems simple enough. But the system is actually quite complex. The classifications are defined differently for each kind of cancer and each stage can include variations to the basic TNM classification . Here are the staging categories and stage grouping for breast carcinoma , for example ( see TABLE: Staging For Breast Carcinoma ).
A breast cancer might be classified as a T2 N1 M0 lesion . This could represent a tumor 2.5 cm (1 in.) in diameter removed from the breast with some involvement of lymph nodes in the armpit but with no evidence of metastasis .
The TNM system has two overlapping classifications, the second having to do with the stage of cancer that represents a composite of the TNM classification. You will see in the tumor section that each tumor is grouped usually in one of four stages. Since there are many possible further TNM subdivisions, these are lumped together. You have to refer to the specific table for each cancer to be sure of the specific stage. For example, the T2 N1 M0 breast cancer described above is a Stage IIB cancer. A T3 N2 M0 cancer is Stage IIIA.
