March is National Colorectal Cancer Awareness month, when public health groups take special pains to promote screening for cancer of the rectum and colon. A leading cause of cancer deaths in the U.S., this disease kills about 50,000 people each year; caught early, however, it has a good chance of being cured.

For screening, physicians commonly recommend colonoscopy as the tool of choice: once every 10 years starting at age 50 for people of average risk, earlier and possibly more frequently for those with a family history of colon cancer or other signs of added susceptibility.

Ever wonder what doctors actually see while you're unconscious?

The video here, courtesy of TheVisualMD, lets you view what doctors observe as they thread a thin tube with a camera on its tip through the rectum and colon (comprising the bulk of the large intestine). They do more than watch the camera, they are able to remove polyps—abnormal growths—both to prevent precancerous polyps from becoming malignant and to examine the tissue for signs of cancer. The video also displays a virtual colonoscopy, which scans the intestines with sophisticated, noninvasive imaging tools.

Colonoscopy is not the only screening option. The American Cancer Society, the U.S. Centers for Disease Control and Prevention (CDC) and others view alternative tests as acceptable as well. Patients can, for instance, collect fecal samples and mail them to a laboratory, which can detect blood in the specimens. But for the analysis to be done properly, the person has to send in samples of three consecutive bowel movements, and the tests do not detect precancerous polyps.

Regardless of how a cancer is found, after diagnosis physicians need to assess the "stage," or extent of its progression, to determine how aggressive treatment needs to be. TheVisualMD offers a lucid description of staging here.

The best way to lower the chances of finding yourself with an advanced stage of colorectal cancer, however, is to undergo the screening. The CDC, which has a program to assist low-income people, argues that if the guidelines were followed, up to 60 percent of deaths from the disease could be prevented.

 Having trouble viewing the video? Click here to go directly to the visualization as provided by