Differences Between Colorectal Cancer and Colon Cancer

Similarities and Differences Between Colon Cancer and Rectal Cancer

surgeon holding a mold of the colon
What is the difference between colon cancer and colorectal cancer?. Credit: ericsphotography

Are colorectal cancer and colon cancer the same thing or are there any differences between the two? How does this tie in to differences between left sided and right sided colon cancers?

Colorectal Cancer vs Colon Cancer

The answer to the question whether colon cancer is the same as colorectal cancer needs some explanation because it is both yes and no depending on the setting.

Often the terms colorectal and colon cancer are used interchangeably.

Sometimes the term colon cancer is used in a way in which it includes both colon and rectal cancer. And sometimes the term colorectal cancer is erroneously used to describe colon cancer, even if the information does not apply as well to rectal cancer.

Despite the term being used interchangeably quite often, there are some important differences between colon and rectal cancer which we will address. It's important to keep in mind, however, that the terms used—even in research papers—do not always address these differences. As noted, the term colorectal cancer may be used in a setting that does not include rectal cancer, and the term colon cancer may be used in a setting which, in contrast, does include rectal cancer.

In other words, there are differences between colon cancer and rectal cancer, but the terms colon cancer and colorectal cancer may or may not include rectal cancer in a particular setting.

(Note: Anal cancer is different than colon or rectal cancer. Currently, a significant percent of anal cancers are felt to be related to infection with the human papillomavirus (HPV)).

History of Colon and Rectal Cancers

Historically, colon and rectal cancers were considered the same, and there are many similarities as noted below.

Yet it's now thought that the two diseases are highly related but distinct entities (and reasons for this will also be noted.)

Anatomy of the Colon - Proximal Colon, Distal Colon, and Rectum

The colon and rectum are both a part of the large intestine, the final destination of the gastrointestinal tract. The colon is approximately five feet long and is separated into the proximal colon—the first portion which is attached to the small intestine, and the distal colon—the second portion which is attached to the rectum. The rectum (which is also part of the colon) is the last 6 to 12 inches of the colon which reaches to the anus.

The colon may also be divided into two sides, that arise from different cells during embryogenesis (the formation of a baby.) The right side (or right sided colon cancers) include the ascending colon (proximal colon) and the left side (left sided colon cancers) include the descending colon, the sigmoid colon, and the rectum (distal colon).

Differences (and Similarities) Between Colon and Rectal Cancer

The distinction as noted above is not between colorectal cancer and colon cancer, but rather between colon cancer and rectal cancer.

As will be discussed, the biggest differences lie in the difficulty of surgery and treatment of locally advanced disease.

Similarities Between Colon Cancer and Rectal Cancer

Incidence  - Colorectal cancer is the third leading cause of cancer related deaths in the United States. Roughly 25 percent of large intestine (colon) cancers are rectal cancers.

Causes - Colon cancer and rectal cancer are more alike than different when it comes to possible causes and risk factors, and how common they are. An association between red meat and cancer is present for both, but much stronger for rectal cancer than for colon cancer. Colon cancer, but not rectal cancer, is also linked with alcohol use.

Symptoms - Symptoms of colon cancer and rectal cancer are very similar, though the symptoms of rectal cancer are more like those of cancers in the distal (farthest from the stomach) portion of the colon. Bleeding from the upper portion of the colon is more likely to appear as brown or black blood, while distal cancers may result in brighter or red blood.

Molecular similarities - From a molecular standpoint, colon cancers and rectal cancers are remarkably similar, down to the type of genetic mutations responsible for their growth. That said, there are also important differences, for example, KRAS mutations are more common in colon cancers than rectal cancers.

Differences Between Colon Cancer and Rectal Cancer

Sex predilection - Colon cancer is pretty much equal between the sexes, whereas rectal cancer is somewhat more common in men than women.

Anatomy - The blood supply, lymphatic drainage, and nerve supply of the colon and rectum are quite different. This is important as cancers metastasize (spread) to other regions of the body via the bloodstream and lymphatic vessels. (Note, this distinction is more between proximal and distal colon cancers, as cancers in the lower intestine before getting to the rectum are more similar to the rectum than the proximal colon.)

Genetic syndromes - There are a number of ways in which hereditary plays a role in the development of colon cancer. Of these, there are two genetic syndromes known to increase risk. Familial adenomatous polyposis (FAP) is more likely to predispose someone to left sided colon cancers (cancers in the distal colon and rectum) whereas hereditary non-polyposis colon cancer (Lynch syndrome) more commonly predisposes a person to right sided colon cancers.

Rate of recurrence - The biggest difference between colon cancers and rectal cancers is the rate of recurrence. Rectal cancer is more difficult to cure, and the rate of recurrence is between 15 percent and 45 percent of patients.

Invasion of Nearby Tissues - Colon cancer, being in the abdomen, has much more "room" around it, whereas rectal cancer occurs in a much tighter spot.  Rectal cancer therefore has a greater chance of spreading early to nearby tissues such as the male and female reproductive organs and the bladder.

Surgical treatments -Treatments for the two cancers differ somewhat. Surgery for colon cancer may be recommended at any stage of the disease, and surgery alone without chemotherapy or radiation therapy is usually the treatment for stage 1 and stage 2 disease. With rectal cancer, surgery may be done for stage 1 to 3 disease, but chemotherapy may be recommended as well, even for stage 1 disease. Radiation therapy is often recommended for rectal cancer, but infrequently for colon cancer.

Difficulty of surgery/surgical approaches - Colon cancer surgery is a much easier surgery in general than rectal surgery. With rectal surgery it is more difficult to get access to the tumor, and dissecting the tumor out from this area of many structures can be more challenging.

Need for a permanent colostomy - People who have surgery for rectal cancer have a much greater likelihood of needing a permanent colostomy than do people with colon cancer, in which a colostomy is the exception rather than the rule. The main problem is the presence of the anal sphincter. With colon cancer, even if a colostomy is done temporarily, it is often possible to go back in and reattach the colon later on (anastomosis.) With rectal cancer, if it is necessary to remove the anal sphincter, this cannot be recreated with surgery and the patient will need a permanent colostomy.

Need for radiation therapy - Radiation is not commonly used for colon cancer, but is needed often for rectal cancer. It may be used in stage 2 and 3 is often used before and after surgery.

Chemotherapy timing - Chemotherapy for colon cancer is often used as an adjunct to surgery in stage 3 patients (and sometimes stage 2) and for stage 4 disease. With rectal cancer, chemotherapy may even be used with stage 1 cancer and is commonly used in stages 2 through 4.

Site of recurrence - Colon cancer is most likely to recur in the liver or lung, but is four times more likely to recur in the liver than the lung. Rectal cancer is a likely or more likely to recur in the lung (lung metastases) than the liver.

Prognosis - The prognosis for colon cancer and rectal cancer is surprisingly similar, but different issues may arise. People with colon cancer are more likely to have short term medical complications but those with rectal cancer are more likely to have surgical complications. These short term complications are overall worse for those with colon cancer than rectal cancers. Rectal cancers are more likely to recur. One of the problems in interpreting information about prognosis is that the colon cancer group includes both those with right sided and left sided (descending and sigmoid colon) colon cancers, and people with left sided colon cancers historically do better than those with right sided colon cancers.

Differences in Left Sided and Right Sided Colon Cancers

Some of the distinctions (at least relative to survival) may not be between colon cancers and rectal cancer but between right sided and left sided colon cancers. There is a fairly big difference in some ways between cancers that begin on the right side of the colon (ascending colon) and those that arise on the left side (descending colon, sigmoid colon, and rectum.) The tissues of the right side originate from different cells embryologically than those of the left side, and it's thought that survival rates for left sided colon cancers are better than those of right sided colon cancers. Some of this data has only recently been noted (at the American Society of Clinical Oncology Annual Meeting in 2016) and it is yet to be determined the significance with regard to treatment approaches.

In other words, some of the differences that have historically been made between colon cancer and rectal cancer may be better understood by differentiating left sided and right sided colon cancers.

Bottom Line

There are several differences between colon cancer and rectal cancer with local control of the disease being a primary difference.

That said, some of the differences beyond surgical access may actually be the differences between cancers in the left sided colon (or distal colon, the descending colon, sigmoid colon, and rectum) compared to the right sided colon (or proximal colon, the ascending colon) since these portions of the colon arise from different tissues during development and have differences in blood supply, lymphatic drainage, and nerve supply. As our understanding of genetics improves, we are also finding some differences in the common gene mutations and molecular basis of these cancers.

Some differences, such as prognosis between colon cancer and rectal cancer are hard to determine. While the short term complications rate of the two diseases may be similar, there are often different causes. As noted, there are often more medical complications for those with colon cancer, whereas rectal cancer which is more difficult to access in surgery often leads to more surgical complications.

Sources:

Hong, T., Clark, J., and K. Haigis. Cancers of the Colon and Rectum: Identical or Fraternal Twins?. Cancer Discovery. 2012. 2(2):117-21.

Lee, Y., Lee, Y, Chuang, J., and Lee, J. Differences in Survival Between Colon and Rectal Cancer from SEER Data. PLoS One. 2013.

van der Slip, M., Bastiaannet, E., Mesker, W. et al. Differences Between Colon and Rectal Cancer in Complications, Short-Term Survival and Recurrences. International Journal of Colorectal Disease. 2016. 31(10):1683-1691.

Venook, A., Niedzwiecki, D., Innocenti, F. et al. Impact of Primary (1º) Tumor Location on Overall Survival (OS) and Progression-Free Survival (PFS) in Patients (pts) with Metastatic Colorectal Cancer (mCRC): Analysis of CALGB/SWOG 80405 (Alliance). 2016 ASCO Annual Meeting. 2016. Abstract 3504.

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