Differences Between Colorectal Cancer and Colon Cancer

Despites similarities, outcomes and treatment can vary

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

Colorectal cancer and colon cancer are often believed to be the same thing or a subset of the other. And, in truth, the terms are often used interchangeably even by health professionals.

To some, the term "colon cancer" can be used to include both colon and rectal cancers. To others, "colorectal cancer" may be applied to describe a malignancy of the colon, even if rectum itself is not involved. Both are fine, but are they correct?

 

Putting semantics aside for a moment, there are some important differences between colon and rectal cancer that bear scrutiny, not least of which are the ways that the two diseases progress.

Anatomy of the 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 attached to the small intestine) and the distal colon (the second portion attached to the rectum). The rectum is the last six to 12 inches of the colon that extends to the anus.

The colon itself is also divided into two sides, a formation of which arises during embryogenesis (the formation of a baby). The right side includes the ascending colon (proximal colon) while the left includes the descending colon, the sigmoid colon, and the distal colon.

Similarities Between Colon and Rectal Cancer

Generally speaking, colon and rectal cancers share distinct similarities, particularly in the way they manifest:

  • Incidence - Colorectal cancer is the third leading cause of cancer-related deaths in the United States. Roughly 25 percent of large intestine cancers are rectal cancers.
  • Risk factors - Colon and rectal cancer are more alike than different when it comes to causes and risk factors. An association between red meat and cancer is present in both, albeit stronger in cases of rectal cancer. By contrast, colon cancer is more strongly linked to alcohol use.
  • Symptoms - Colon and rectal cancer are very similar in terms of their symptoms, although some can vary. For example, bleeding from the upper portion of the colon is more likely to have brown or black blood, while distal cancers typically result in a brighter, red blood.
  • Genetics - From a molecular standpoint, colon and rectal cancers are remarkably similar, down to the type of genetic mutations responsible for their growth. There is some variation, but, on the whole, the two cancers are clearly related.

Differences Between Colon and Rectal Cancer

Despite similarities, there are striking differences between the two cancers:

  • Sex predilection - Colon cancer is distributed pretty much equally 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.
  • Disease recurrence - This may be the biggest differentiator. Generally speaking, rectal cancer is more difficult to cure, with recurrence developing in between 15 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 the greater chance of spreading to nearby tissue.
  • Surgery - Surgery for colon cancer may be recommended at any stage of disease, while surgery alone without chemo or radiation therapy is typically prescribed for stages 1 and 2. By contrast, surgery for rectal cancer can be performed from stages 1 to 3, often in conjunction with chemo and radiation therapy.
  • Difficulty of Surgery - Surgery for colon cancer is a much simpler compared to rectal cancer. With rectal surgery, it is more difficult to access the tumor and to avoid many of the structures surrounding it.
  • Colostomy - People who have undergone rectal cancer surgery have a greater likelihood of a permanent colostomy. This is because the removal of the anal sphincter if often required, which can neither be replaced nor reconstructed.
  • Radiation therapy - Radiation is not commonly used for colon cancer but is for rectal cancer (predominately stage 2 or 3).
  • Chemotherapy - Chemotherapy for colon cancer is often used as an adjunct to surgery in stages 3 and 4 (and sometimes 2). With rectal cancer, chemotherapy may be used even with stage 1 disease.
  • Postoperative complications - People with rectal cancer are more likely to have post-surgical complications when compared to those with colon cancer surgery, who are more prone to short-term medical complications.

Colon Cancer Research

There also appear to be a fairly big difference between cancers that originate on the right side of the colon (ascending colon) and those that arise on the left (descending colon, sigmoid colon, rectum).

We already know that the tissues of the right side have different cells than those of the left, a vestige of embryonic development. Data has since shown that survival rates for left-sided cancers tend to be better than those of the right. While these findings are considered significant, it has yet to be determined whether this will alter treatment approaches.

As our understanding of genetics improves, we are also beginning to find differences in the common gene mutations and molecular basis for these cancers. By better understanding these differences, scientists hope to find immunologic and biogenetic approaches to specifically target these unique cells, allowing for control – and even eradication – of the disease.

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. November 12, 2013; 8(11): e78709.

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, Chicago, IL. June 2-6, 2016; abstract 3504.

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