Colorectal Cancer Basics
What is "colorectal cancer"?
Colorectal cancer is cancer that occurs in the colon and in the rectum. Cancer is when normal cells develop genetic mutations that allow them to grow without the controls that normal healthy cells have. The cells grow locally but can then spread to other organs which can make somebody quite ill. The colon is the part of the intestine that connects the small intestine around the abdomen to the rectum, which then connects to the anus, where waste is discarded from the body. Colorectal cancer happens anywhere along that tract.
How common is colorectal cancer?
Colorectal cancer is quite common. Colorectal cancer is the third most common cancer in the United States. Colorectal cancer is the second leading cause of cancer death. About five percent of people, over their lifetime, will develop colorectal cancer, which means 1 in 20 people will be affected by it. But the incidence of colorectal cancer is actually decreasing, as is the mortality from colorectal cancer, so the number of colorectal cancers are less, and when people are diagnosed with colorectal cancer, they're living longer and doing better.
What causes colorectal cancer?
We don't know exactly what causes colorectal cancer. It is partly due to genetics; people are born with certain predispositions to developing colorectal cancer. The environment also has a factor in causing colorectal cancer. This includes the food we eat, the amount of exercise we get, whether we smoke, whether we drink alcohol and general toxins in the environment. Everything can combine to cause colorectal cancer and it's very hard to say to any one individual what caused their colorectal cancer.
What are the risk factors for colorectal cancer?
There are many different risk factors for colorectal cancer. Advancing age is probably the largest. Greater than ninety percent of all colorectal cancers happen in people over the age of fifty. Having a family history of colorectal cancer also will increase your risk. If you've ever developed a polyp, that can increase your risk for colorecal cancer because colorectal cancer usually starts as polyps then they advance into cancer. Having a genetic predisposition, for instance FAP or another inherited cancer syndrome can increase your risk of developing colorectal cancer as well. Any kind of chronic inflammation in the bowel can increase your risk as well. So if you have inflammatory bowel disease, ulcerative colitis, or Crohns disease that can increase your risk of colorectal cancer too. Some other risk factors for colorectal cancer include toxins that we take in. People who smoke can increase the risk of colorectal cancer by about thirty to forty percent compared to those who do not smoke. Alcohol, especially heavy alcohol consumption can increase one's risk too. Other factors which can increase one's risk for colorectal cancer include being overweight, not exercising. Those have been associated in epidemiologic studies with increases in colorectal cancer. And then also extra exposures, for instance if somebody's gets radiation for prostate cancer there has been a slight increase risk of developing colorectal cancer in those individuals. One's ethnic background can increase one's risk for developing colorectal cancer. For instance, Ashkenazi Jews carry a greater incidence of genetic mutations which predispose them for developing colorectal cancer over their lifetime. In addition, African Americans have a greater risk of developing colorectal cancer. It's not clear if that's a genetic predisposition or if that's something that's environmental because diet also plays a role too. And diets that are higher in fats and lower in fiber and lower in certain vitamins have been associated with greater risks of colorectal cancer.
Can colorectal cancer be cured?
Colorectal cancer can absolutely be cured. The key is prevention and the key is screening; finding polyps before they become cancers. Have them removed and you can actually prevent the cancer from developing altogether. If a cancer does develop, if it's found early, it can be removed surgically and the cancer can be cured at that point. Some individuals, because of lymph node involvement, or larger size of the tumour, may need some adjuvant chemotherapy (in other words, chemotherapy after the surgery) which can improve the chances of cure as well. In some individuals who have metastatic disease (meaning the cancer has already spread beyond the colon and usually into the liver), if all of the cancer can be surgically resected then there's a chance for even the metastatic disease to be cured. This is unusual for cancer because in other types of cancer once the cancer has metastisised, it's usually not curable. However, in colorectal cancer some individuals can be cured, even with metastatic disease, so it's a very curable cancer.
How fast can colorectal cancers grow?
In general, colorectal cancers are slow growing. Colorectal cancers develop over many years. They start off as small growths in the intestine or in the colon called polyps. These polyps can then grow larger and start to become atypical. The polyps develop genetic mutations which allow the cells to grow faster, and then start to invade through the colon wall, and that's when the colorectal cancer actually develops. But these polyps can be found years before the event that turns them into colorectal cancer ever happens. And that's why screening is so important for colorectal cancer so that we can go in, find these polyps and remove them before they ever become colorectal cancer. Once the polyps have turned into colorectal cancer the speed of growth can increase and at that point the cancers can grow faster, but in general colorectal cancers are slow growing initially for many years before they become faster growing.
What are the stages of colorectal cancer?
There are four stages to colorectal cancer, like most cancers; stage 1, 2, 3, and 4. Stage 1 colorectal cancer is a localised cancer, meaning it's just within the wall of the colon. Surgery alone is curative in the majority of individuals. Stage 2 colorectal cancer is when the cancer has gone through the wall of the colon. Surgery alone cures most of these but there may be a role for adjuvant chemotherapy (meaning chemotherapy after the surgery) in some individuals. Stage 3 colon cancer is where the tumour has grown through the wall of the colon and there are also lymph nodes that are involved. This can be cured with surgery alone, but there is a greater risk of relapse so usually, adjuvant chemotherapy is recommended. Stage 4 colorectal cancer is when the cancer has spread beyond the colon; It's now in other organs, usually the liver, but it can spread to the lungs and other organs in the body. Some stage 4 colorectal cancers can be cured if all of the tumour can be surgically removed, but that's usually a minority of them. Usually when somebody has stage 4 colorectal cancer it's unfortunately no longer curable. It's treatable, but it's not curable at that point.
What is "familial adenomatous polyposis" syndrome or "FAP"?
FAP, or familial adenomatous polyposis, is a genetic predisposition to developing colorectal cancer. It is a certain genetic mutation that causes people to develop colon polyps at a very young age, usually in their teens. When people are screened with colonoscopy, their colon is lined with these polyps which are all ticking time bombs for developing colorectal cancer over many years. Greater than 90% of individuals with FAP have some colorectal cancer by the age of 45. That's why it is recommended for these individuals to get aggressive screening very early in life and also to consider a colectomy, which basically will reduce the chances of developing colorectal cancer almost to zero.
What is a "polyp"?
A polyp is a growth of tissue on the inside of the colon. There are many different types of polyps. There are sessile polyps, which are flat against the wall of the colon, and pedunculated polyps, which have a small stock to them. Polyps can be assessed by a colonoscopy, where doctors go into the colon with a tube that has a small camera on the end in order to look around, and use small forceps to take a biopsy and remove polyps. It's important to be evaluated for polyps and to get polyps removed because over time they can turn into colorectal cancers.
What is an "adenoma"?
An adenoma is a specific type of polyp that is a growth of glandular tissue. An adenoma is not cancerous, per se, and nearly two-thirds of all polyps are adenomas, but adenomas can turn into cancer over many years. They can become atypical and turn into cancer as they develop genetic mutations over time. It's important to be assessed for polyps and for adenomas with a colonoscopy and to have them removed, to prevent them from ever turning into colorectal cancer.
What is an "adenocarcinoma"?
An adenocarcinoma is cancer of glandular tissue. Adenocarcinoma is a general descriptive term for a type of cancer that can actually happen in many different tissues: in the breast, in the lung and in the colon. Adenocarcinoma is the most common type of colorectal cancer, occurring when the glandular tissue lining the colon and rectum becomes cancerous.
Why are Eastern-European Jews at high risk for colorectal cancer?
In Ashkenazi Jews, they carry certain genetic predispositions to cancer. In particular they carry the APC gene and that's the adenomatous polyposis coli gene, which is an important gene for repairing DNA damage. And when DNA damage does not get repaired it can increase ones risk for developing cancer. And the APC gene inparticular increases ones risk of developing colorectal cancer. And so that is why this certain ethnic subgroup has a greater risk of colorectal cancer.
Why do African Americans have the highest death rates from colorectal cancer?
I don't think anybody really knows why African Americans have a higher death rate from colorectal cancer. There's probably a number of different factors which play into it. Some of them genetic, with the type of cancers that African Americans are developing are slightly more aggressive. Another issue of access to health care, and people not getting screened when cancers can be found earlier at a less aggressive, more curative stage. It's very important for everybody of any descent to make sure that they get screened for colorectal cancer because it is a very curable cancer when found early.
