Stage IV colorectal cancer
Stage IV is the most advanced stage of colorectal cancer. If you have been diagnosed with stage IV colorectal cancer, it means that the cancer has metastasized to distant sites, such as the liver or lungs. The cancer may or may not have grown through the wall of the colon or rectum, and lymph nodes may or may not have been affected.
Stage IV colorectal cancer is further divided into two categories, depending on whether or not the metastasis has affected more than one organ. The original tumor can be of any size and lymph nodes may or may not be involved, but if the cancer has spread to one different organ it is considered stage IVA, while more than one organ would be defined as stage IVB.
Stage IV colorectal cancer can be defined by any T or N category, with the only difference stemming from whether the M1 or M2 assignment is more appropriate.
In both forms of stage IV colorectal cancer, the tumor can be of any size (T), and lymph nodes may or may not be involved (N). M1a indicates that the cancer has spread to just one organ, while M1b would mean that more than one organ has been affected.