In short: no. IBS is not a progressive condition; it does not "turn into" colon or rectal cancer or to IBD. IBS is a frustratingly difficult condition to have, and to treat, but it does not cause the intestines to develop ulcers or cancers. Even though IBS can be very painful and disruptive, it is considered a functional disorder, and does not cause damage to the digestive tract. Although patients with IBS don't go on to develop IBD or cancer, the symptoms sometimes overlap, so misdiagnoses do occasionally occur.
Source:
National Digestive Diseases Information Clearinghouse. "Irritable Bowel Syndrome." National Institutes of Health Publication No. 07–693 Sep 2007. 15 Feb 2011.

