The TNM system, established by the American Joint Committee on Cancer, is commonly used to stage bile duct cancer. The TNM system uses three key factors to determine a cancer’s stage:

T (tumor): This describes the size of the original tumor.

N (node): This indicates whether the cancer is present in the lymph nodes.

M (metastasis): This refers to whether cancer has spread to other parts of the body.

A number (0-4) or the letter X is assigned to each factor. A higher number indicates increasing severity. For instance, a T1 score indicates a smaller tumor than a T2 score. The letter X means the information could not be assessed.

Once the T, N and M scores have been assigned, the cancer is staged accordingly:

Stage 0: The cancer is found only in the innermost layer of the bile duct (mucosa) and has not spread to the deeper layers. In this stage, the disease has not invaded lymph nodes or any other distant sites in the body.

Stage I (stage 1 bile duct cancer): Still contained within the bile duct, the cancer now extends into the deeper layers of the bile duct wall (muscle or fibrous tissue layer). It has not spread to lymph nodes or other distant sites.

Stage II (stage 2 bile duct cancer): The cancer has now spread through the wall of the bile duct into nearby fat (IIB) or liver tissue (IIB).

Stage III (stage 3 bile duct cancer): Stage III bile duct cancer is divided into two subcategories:

• Stage IIIA: The disease has spread to the main portal vein, the common hepatic artery, duodenum (first part of the small intestine), colon, stomach or abdominal wall, but not beyond. The cancer has not spread to the lymph nodes or distant sites.
• Stage IIIB: Cancer cells are found in nearby lymph nodes, but the cancer has not spread to distant sites.

Stage IV (stage 4 bile duct cancer): Stage IV bile duct cancer is divided into two subcategories:

• Stage IVA: The cancer is growing and has spread to the main blood vessel and the lymph nodes but not distant sites.
• Stage IVB: The cancer has either spread to lymph nodes away from the tumor or it has spread to distant sites.

Next topic: How is bile duct cancer diagnosed?