Colonic cancer can spread locally or via the lymphatics, bloodstream or transcoelomically around the peritoneum. Direct spread can be longitudinal, transverse or radial. Radial spread to adjacent organs has the greatest impact on surgical resectability, as an adequate oncologic resection can still be achieved, despite longitudinal spread, by extension of proximal and distal margins. Radial spread may be retroperitoneal into the ureter, duodenum and posterior abdominal wall muscles, or intraperitoneal into the small intestine, stomach, pelvic organs or the anterior abdominal wall.
In general, involvement of the lymph nodes by the tumour
progresses in a gradual manner from those closest to the bowel
along the course of the lymphatic vessels to those placed centrally.
However, this orderly process does not always occur.
The liver accounts for the majority of distant metastases presumably via the portal vein. Around a third of patients will have liver metastases at the time of diagnosis and 50 per cent will develop liver metastases at some point accounting for the majority of deaths. The lung is the next most common site metastases to ovary, brain, kidney, brain and bone are less common. Occasionally, patients will present with metastatic disease in the lungs without evidence of liver metastases.
Colorectal cancer can spread by way of cells dislodging from the serosa of the bowel or via the subperitoneal lymphatics and settling on other structures within the peritoneal cavity, including peritoneum and omentum. Prognosis is typically grave in thesecircumstances although some units have reported encouraging results in selected patients treated with the combination of aggressive cytoreductive surgery and intraperitoneal chemotherapy.