Invasive colorectal cancer clinico-pathological stage is defined into four summary groups (Stages I-IV) based on the pathological TNM staging system:

The TNM staging system uses the letters 'T' to represent the tumour, 'N' to represent regional lymph node involvement and 'M' to represent distant metastases, with a numeric subscript (not subscripted in the table above) to indicate the degree of dissemination. For example, T1N0M0 designates a small localised tumour, T2N1M0 is a larger primary tumour that has extended to regional nodes, and T4N3M3 is a very large legion involving regional nodes and distant sites.

Colorectal cancer is considered to have reached at least Stage III if there is any lymph node involvement, and at Stage IV if there are any distant metastases.