| Mechanism | Site | Route |
| Direct invasion | ||
| Any organ beside the tumour | Direct growth | |
| Haematogenous | ||
| Liver | Via the portal vein | |
| Bones | Through the liver and lungs
Via lymphatics into the bloodstream and through the lungs Retrograde flow through veins due to occlusions and collateralisation |
|
| Lungs | Through the portal system and liver
Via lymphatics into the bloodstream |
|
| Lymphatic | ||
| Lymph nodes | Via lymphatic channels | |
| Trans-coelomic | ||
| Peritoneal deposists (carcinomatosiis peritonei | Shedding of viable tumor cells from the surface of the bowel. | |
| Trans-Luminal | ||
| Intestinal anastamosis | ? one source of local recurrance | |
Colorectal cancer spreads via the blood stream, the lymphatics, across the peritoneal cavity and viable intraluminal tumor cells are thought to be one of the causes of anastamotic recurrence.
Metastatic cells may leave the tumour via lymphatics or capillaries. Tumour cells travel in the portal system to the liver, which is the major site of metastatic deposits from colo-rectal cancer. Most tumor cells that get into the portal system are thought to become caught in the liver. Patients with isolated metastatic deposits in the liver may be cured of their cancer by resection of the metastatic deposit in the liver. Tumor cells also spread via the lymphatics where they may cause metastatic deposits in the lymph nodes, these serve as a good marker for the possbility of diffuse metastatic disease and poor outcome. Some tumor cells may pass through the lymph nodes into the systemic circulation via the thoracic duct. Once in the systemic cirulation they will often pass into the capilleries of the lumg where they may cause pulmonary secondary deposits. If they bypass the lung or pass through it the tumor cells may establish tumor deposits in any of the capillary beds in the body.
Another route of spread of colo-rectal cancer is through the peritoneal cavity where they may ultimatly cause carcinomatosis peritoneii. Such viable tumour cells in the peritoneal cavity are through to the the main source of metastatic disease in laparotomy wounds and laparoscopic port sites.
Endoluminal spread may also occur, viable tumour cells may be implanted by the surgeon in an anastamosis and subsequently cause a local recurrance