Melanoma of the Colon and Rectum

Uncommon form of cancer usually has worse outcomes

Colon cancer illustration
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While malignant melanoma of the colon and rectum is not a common condition, it can occur when the cancer has either spread (metastasized) from a tumor on the skin or returned in a person who has previously been treated.

It is estimated that less than two percent of colorectal cancers are the result of melanoma. However, when it does occur, it is usually very aggressive and far more difficult to treat.

At the same time, because it is so rare, cancers of this type are easily missed during initial and even follow-up diagnosis.

Secondary Colorectal Cancer in Persons With Melanoma

When metastasis is involved, the melanoma would be considered the "primary cancer" while any organs affected by the spread of melanoma would be "secondary."

The relatively rarity of secondary colorectal cancer is due to the types of cells that melanoma affects. Melanoma originates in a special type of cell, called a melanocyte, which gives our skin and eyes their color.

In 96 percent of cases, melanoma will originate in the skin. It can then metastasize and spread throughout the lymphatic system to affect other organs. More often than not, it will be the non-skin organs containing melanocytes which will be most affected. These include the eyes and mucosal tissues of the mouth, nose, anus, rectum, and vagina.

As such, the rectum is more likely to be affected by melanoma metastasis than the colon (which has few melanocytes).

With that being said, malignant tumors will typically "recruit" nearby tissue and, in doing so, enable the spread of cancer from the rectum and/or anus to the adjacent colon.

The one group most at risk of secondary anal or rectal cancer are people with advanced HIV disease. By contrast, primary melanoma of the colon or rectum is so rare as to be considered of negligible risk.

Second Cancer in Persons With Treated Melanoma

As opposed to secondary cancer, any malignancy that develops after the successful treatment of melanoma is considered a "second cancer" (a.k.a. second primary cancer). While the second cancer is "new" and is in no way associated with the first, its appearance is often linked to the same factors that gave rise to cancer in the first place.

Being successfully treated for melanoma shouldn't suggest you can't get other types of cancer. The very fact that you’ve had melanoma places you at higher risk. Second cancers can even include skin cancers that have no connection to the first and, as such, cannot be considered a recurrence or relapse.

Other second cancers seen in people previously treated for melanoma include:

  • breast cancer
  • kidney cancer
  • non-Hodgkin lymphoma (NHL)
  • prostate cancer
  • salivary gland cancer
  • soft tissue cancer
  • small intestine cancer
  • thyroid cancer

Colorectal cancer, by contrast, is not seen in higher rates than would be expected in the general population.

Life Expectancy and Survival Times

Secondary colon cancers in person with melanoma are associated far shorter survival times (an average of 10 months) due primarily to late diagnosis. According to a study from the Mayo Clinic, the average time between diagnosis of the primary melanoma and the secondary colon cancer was an astonishing 7.47 years.

Among the patients studied, the surgical removal of the cancer was seen to quadruple life expectancy from an average of seven months to just over 27.

Sources:

Katsanos, A.; Tsianos, V.; and Tsianos, E. "Metastatic melanoma in the stomach and large bowel." Annals of Gastroenterology. 2010; 23(4):322-324.

Tessier, D.; McConnell, E.; Young-Fadok, T.; et al. "Melanoma metastatic to the colon: case series and review of the literature with outcome analysis." Diseases of the Colon and Rectum. 2003; 46(4):441-447.

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