Colon-rectal Cancer

The Annals of Internal Medicine published that colonoscopies are still very effective in detecting colon-rectal cancer, but they're only good at doing so in cancers found on the left side [descending] of the colon, not on the right side (ascending). Possible reasons the test favors the left side include the form and structure of the colon's different parts, and the different types of polyps that are commonly found on the right side versus the left side.

The colon has four different parts, including the ascending and descending colon, which are physically very different.

One possibility is the polyps on the left side of the colon are sort of mushroom-shaped with a stem, thus making them easier to see (and to remove). Whereas the right side often has more squatter-looking polyps that don't have stems, or are sometimes flat and thus harder to see.

Other possibilities are that it's harder for an endoscope to reach the right side than the left side, or that the treatment you drink to clean out the colon before you get screened isn't being taken properly or there's a combination of these factors going on.

Colon-rectal cancer is the third-leading cause of cancer deaths in the United States, but screening can prevent cancer, because from the time you detect polyps in a colonoscopy, it will take 10 to 15 years to turn into cancer. So, if you remove the polyps before they turn into cancer, you can avoid it altogether