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 of these conditions sometimes overlap, so misdiagnoses do occasionally occur.
American Society of Colon & Rectal Surgeons. "Irritable Bowel Syndrome." FASCRS.org 2012. 28 Jun 2013.
National Digestive Diseases Information Clearinghouse. "Irritable Bowel Syndrome." National Institutes of Health Publication No. 07–693 2 Jul 2012. 28 Jun 2013.