Local extension in the gut wall
A local cancer can expand locally into the gut wall and along it. The latter can be both circumpherentially and longitudinally. Tumor nests may be found in the gut wall as far as 1 cm from the macroscopic tumor.
Local extension in the pericolic/-rectal fat
In contrast to the extension in the bowel wall, microscopic tumor may be found in the pericoloc/ perirectal fat up to 5 cm from the macroscopic margin of the tumor. This may be located within the fat itself or within lymph nodes, and may be found both orally and anally to the tumor. It is therefore recommended to resect at least 10 cm of colon and pericolic fat away from the cancer and at least 5 cm in the rectum.
Direct invasion of neighboring organs
Cancer in the colon can directly invade the urinary bladder, small bowel, duodenum, the internal genitals, the abdominal wall, retroperitoneum and seldom other organs.
When the cancer is located in the intraperitoneal part of the gut it can grow through the peritoneum and give rise to intraperitoneal seeding of tumor cells and peritoneal carsinomatosis. This is present in around 8% of colon cancer at operation, more seldom in rectal cancer.
Cancer in the rectum can cause:
- Infiltration in the pelvic wall, ureter, large pelvic vessels-and nerves
- Infiltration into vagina, uterus, prostate, seminal vesicles, prostate, urinary bladder
Lymphatic vessels are located in the submucosa and deeper parts of the gut wall. During infiltration of the superficial part of the submucosa, lymphogenic spreading is very infrequent (< 5%). During infiltration of the deeper parts of the submucosa and the muscularis propria lymphogenic spreading appears in 15-20%, and even more frequent when infiltrating the pericolic fat. Metastases appear in local lymph nodes 15-20% of all operated for colorectal. Among all patients operated for intestinal cancer 35-40% have metastases to the regional lymph nodes.
The regional lymph nodes are divided into different locations:
- Epiploic (close to the gut), N1 ( Japanese classification)
- Intermediate, N2
- Central- apical, N3
This division is the basis for the D1-, D2-, D3- dissections.
The tumor can further spread along the lymph nodes at the aorta, in the liver ligament, mediastinum and supraclavicularly. From rectal cancer the tumor can spread to mesorectum and along the inferior mesenteric vessels (regional metastases). Metastases can also appear in the lymph nodes of the pelvic wall, and very seldom (low cancer/ obstruction of oral lymph flow) to the inguinal lymph nodes (distant metastases).
Colo-rectal cancer can infiltrate into extramural vessels and from here migrate through the blood stream out of the loco-regional area and develop distant metastases. These will primarily appear in the liver (15-20% at the time of diagnosis), lungs (5%), and more seldom to the skeleton, brain and kidneys.
Microscopic accumulations of tumor cells can often be found in the bone marrow without development of clinical metastases.