Bile Bile ducts are thin tubes that connect the liver with the small intestine. These ducts transport bile (digestive fluid) formed in the liver and the gallbladder.
The bile duct system consists of a series of ductules (small tubes) in the liver that combines into ducts called the intrahepatic bile ducts. The duct coming from the gallbladder is called the cystic duct. The cystic and intrahepaticducts merge to form the common bile duct, which joins with the pancreatic duct and then reaches into the duodenum (beginning of the small intestine).
Cancer in any part of these bile ducts is termed as cholangiocarcinoma. Adults aged above 65, usually males, and those having colitis or other forms of liver disease are at increased risk of having cholangiocarcinoma. The tumors involved in bile duct cancer metastases via the lymphatic system and then into the blood vessels that go into the liver.
Classifications of bile duct cancer
Bile duct cancer can be divided into two groups based on their location: intrahepatic (inside the liver) and extrahepatic (outside the liver).
a) Intrahepatic bile duct cancer:
These cancers originate in the ductules inside the liver. Very few bile duct cancers (5–10%) are intrahepatic, andthey are also known as intrahepatic cholangiocarcinomas. The different methods for analysis of intrahepatic bile duct tumors under a microscope (histopathologic study) are as follows:
- Periductal-infiltrating tumor growth pattern
- Intrahepatic cholangiocarcinoma.
- The combination of periductal-infiltrating mass-forming growth pattern.
- Mixed hepatocellular cholangiocarcinoma.
- Mass-forming tumor growth pattern.
b) Extrahepatic bile duct cancer:
Most bile duct cancers are extrahepatic, and so are found outside the liver. Extrahepatic bile ducts have distal and hilum regions and cancer can form in either of these regions.
- Perihilar bile duct cancer: These cancers are mostly present in the hilum region, at the end portion of the liver where the left and right bile ducts move outside the liver. Cancer in the perihilar bile duct is also termed as perihilar cholangiocarcinoma or Klaskin tumors.
In perihilar bile tumor, the adenocarcinomas frequently foundinclude the following:
- Squamous cell carcinoma.
- Signet-ring cell carcinoma.
- Adenocarcinoma, NOS.
- Adenocarcinoma, intestinal type
- Carcinomain situ.
- Clear cell adenocarcinoma.
- Mucinous adenocarcinoma.
- Adenosquamous carcinoma.
- Distal extrahepatic bile duct cancer: In this kind of cancer, tumor cells are present in the distal region of the bile duct. Another name for distal extrahepatic bile duct cancer is extrahepatic cholangiocarcinomas. In extrahepatic bile duct tumor, adenocarcinomasare frequently found. The types of distal extrahepatic bile duct cancer are as follows:
- Oat cell carcinoma, also known as small cell carcinoma
- Undifferentiated carcinoma.
- Spindle and giant cell types.
- Small cell types. Noninvasive, papillary carcinoma.
- Invasive, papillary carcinoma.
- NOS, Carcinoma.
Different stages of bile duct cancer
The TNM system is used as a method of staging for all cancers. Knowledge of the stage of the cancer helps the physician to decide about the mode of treatment. In bile duct cancer, they provide the following crucial information:
T (tumor)—specifies whether the primary tumor has spread to the adjacent tissues or organs through the duct wall.
N (nodes)—informs whether the cancer has spread to the neighboring lymph nodes responsible for the immune system of the body.
M (metastases)—reveals whether there is metastasis (spread) of the cancer to other organs such as the liver, the abdominal cavity lining, or the lungs.
The term “TNM” is followed by alphabets or numbers 0–4, which give in-depth information about each of these aspects. The stages (0–4) of bile duct cancer are as follows:
Stage 0: cancer is located only in the mucosa (lining) of the bile duct and has not gone into the deeper layers. It has also not affected any of the lymph nodes or other organs of the body.
Stage I: cancer is still inside the bile duct, but has penetrated into the other layers of the bile duct wall, such as the muscle and fibrous tissues; it has not metastasized to other body parts.
Stage II: cancer has spread to neighboring liver (IIB) or fat (IIB) tissues, through the bile duct wall.
Stage III: sub-classified as A and B
IIIA—cancer has metastasized only to the main portal vein, to the initial part of the small intestine, stomach, and colon, but not to the lymph nodes or other sites.
IIIB—cancer has spread to the neighboring lymph nodes, but not to distantsites.
Stage IV: sub-classified as A and B
IVA—cancer is growing and has spread to nearby lymph nodes and blood vessels, but not any further.
IVB—cancer has spread to lymph nodes that are far away from the tumor or even to distant sites.
The position and severity of the cancer growth determines the outlook of bile duct cancer. Cholangiocarcinomasare treated by stenting, radiotherapy, chemotherapy, and photodynamic therapy. Unfortunately, it is possible for tumors in bile ducts to reoccur even after theyhave been removed. After surgery, the 5-year survival rate among patients is 20–50%.
Reviewed by Afsaneh Khetrapal BSc (Hons)