About 95 percent of colorectal cancers start with a polyp, which are benign, slow-growing clusters of cells that grow on the intestinal wall and usually have a mushroom-like appearance. Polyps are common - about 30 to 40 percent of adults 50 and older develop them - and usually harmless - most polyps won't ever turn into cancer. However, because polyps often develop without causing any symptoms, colorectal cancer screening is a crucial part of your regular medical exam if you're age 50 or older.
