Dear OncoLink "Ask The Experts,"
When is radiation used after colon surgery?
Richard Whittington, MD, Associate Professor of Radiation Oncology at the University of Pennsylvania School of Medicine, responds:
Cancer of the colon and rectum are actually the same tumor in different locations. When the surgeon takes out the tumor treatment depends on the margin of safety of the removal. The easiest way to think about it is as if the colon and rectum are a length of pipe. Tumors that break through the wall are like a leak in the pipe that may contaminate their surrounding soil and tumor cells in lymphatic fluid and lymph nodes are like ground water contamination. When the colon is inside the peritoneal cavity of the abdomen it moves about as if it is on a very long tether drawing its' blood supply through the long thin sheet of the mesentery. This is as if the pipe is elevated on a platform. There is not any nearby soil to get contaminated. The surgeon gets a wide margin of safety around the tumor like the pipeline maintenance crew can remove the defective segment of pipe and the platform to prevent contamination of the surrounding soil. Still it is possible for the tumor to spread to lymph glands like the leak in the pipe may contaminate ground water. In the last 6 inches of its' course, the colon becomes the rectum which simply means it leaves the peritoneal cavity. Here it may lie on the bladder, the uterus or prostate or the sacrum (tail bone), which cannot be safely removed. It is as if the pipe were lying on a rock field that is too big and extensive to remove. Here there is a risk of contamination of the surrounding soil as well as the ground water. Since there are much higher concentrations of contaminants on the soil than in the ground water, they are managed differently.
They bring in booms and sponges to sop up as much of the contamination as possible because the concentrations are so high. They use detergents and other chemicals to treat the remaining contamination and the ground water. Similarly, Radiation is more effective at dealing with a higher concentration of tumor cells but can only treat a defined area and not the whole body, while chemotherapy can treat isolated cells and does treat the whole body. We have also found that chemotherapy will make tumor cells more sensitive to the effects of radiation without having anywhere near that effect on normal cells. This is why chemotherapy and radiation are used together. In several trials they have compared surgery alone vs. surgery + chemotherapy vs. surgery + radiation therapy vs. surgery + radiation therapy + chemotherapy. In general they found that chemotherapy delayed the regrowth in the tissues around the tumor but the overall risk did not appreciably change, so patients lived longer but there was only a small increase in the cure rate. Radiation sharply reduced the risk of any regrowth of the tumor in the surrounding tissues but did not have much effect on the risk of spread elsewhere in the body and did not increase the cure rate at all. The combination effectively treated both problems and did increase the cure rate. The questions now are which chemotherapy and what tumors need radiation. In general tumors of the colon inside the peritoneal cavity do not get radiation unless the tumor is stuck to something or growing into another organ (T4 tumor). Chemotherapy is used when the lymph nodes are involved and when radiation is given for a T4 tumor. In the last 6 inches, the rectum, chemotherapy and radiation are given when the tumor has broken through the wall of the rectum, even if it is not stuck to anything, and when the lymph nodes are involved.