The exact cause of gall bladder cancer is not known but there are a number of conditions which increase the risk of these tumours developing. These include:

• gall stones: about 8 out of 10 people who develop gall bladder cancer will also have gall stones. It has been suggested that damage to the lining of the gall bladder might lead to a cancer developing. (It is also true that if gall stones are large, more than 3cm (1 ½ inches) across, the risk of a cancer developing increases.) Despite all this less than 1 in 50 people who have their gall bladder removed for gall stones will be found to have a cancer. So although gall stones are very common in people who have gall bladder cancer, gall bladder cancer is quite rare in people who have gall stones.
• sometimes benign tumours, called polyps, can develop in the lining of the wall of the gall bladder. Over a period of many years these polyps can sometimes change into cancers. This is more likely if they are large (greater than 1cm, about ½ and inch, across). This change usually only seems to happen if there are gall stones in the gall bladder.
• Gall bladder cancer is also slightly more common in people who are born with abnormalities of the bile ducts, or people who have a condition called porcelain gall bladder in which calcium forms in the wall of the gall bladder. About 1 in 5 people who have a porcelain gall bladder will go on to develop a gall bladder cancer.

Despite these different links to other conditions gall bladder cancers can sometimes occur for no obvious reason.