The usual treatment for bowel cancer (cancer of either the colon or rectum) is an operation to take away the growth. Sometimes, however, the cancer is only discovered at a late stage when it has spread too far for an operation to be possible. 

In this situation, the cancer often causes narrowing of the bowel which can cause problems with digestion and may cause the bowel to become completely blocked (called an intestinal obstruction). Putting in a stent is one way of easing the problems caused by narrowing of the bowel due to the presence of the cancer.

A stent is a thin metal cylinder which can be slipped through the narrowed bit of the bowel, where the cancer is, and then expanded to make a rigid tube, which eases the blockage.

There are a number of different stents used for bowel cancer but most are made of a nickel/titanium alloy (called nitinol). To put them in place the patient is given sedation, with an injection into a vein. A colonoscope, which is a sort of flexible telescope, is then passed up through the back passage to where the tumour is.  A thin guidewire is slipped through the narrowed bit of bowel, and the stent is threaded over this guide wire. Next, an x-ray is taken to make sure it is in the right position. The stent is then expanded to open up the narrowing in the bowel.

In the past, the usual way of avoiding problems due to narrowing of the bowel by an inoperable cancer would have been to do an operation.This would have involved cutting the bowel just above where the cancer was and bringing the cut end of the bowel out through the skin of the front of the belly to make a colostomy. This would by-pass the narrowed area of bowel and avoid any problems from the narrowing, but it would mean having a colostomy.

Stents are a recent development. They have only been used for large bowel cancers since the late 1990s. They are not suitable for everyone but they can sometimes offer an alternative to surgery and needing a colostomy for people with advanced bowel tumours. They allow the bowel to continue to work almost normally despite the presence of the cancer.

Stents are normally quite safe but very occasionally they can cause complications. These include bleeding from the bowel, or pain, both of which are usually temporary and settle in a day or two. There is also a small risk that the stent might puncture, or perforate, the bowel when it is being put in place. These problems only affect about 1 in 20 people who have a stent inserted.

Sometimes the stent may not work, either because it is impossible to get it in position in the first place, or because it moves or becomes blocked by the bowel contents, or because the tumour grows over one or other end of the tube. However these difficulties are quite uncommon.

The stent does only ease the narrowing of the bowel, caused by the cancer, and reduce the risk of the bowel becoming completely blocked (intestinal obstruction).  It does nothing to actually treat the cancer. Other measures, like radiotherapy or chemotherapy, may be offered as well in order to try and control the underlying cancer.