**2.4 Cancer risk in IBD**

The increased risk of colonic adenocarcinoma in patients with ulcerative colitis and Crohn's colitis is well documented (Rutter et al., 2006, Jess et al., 2006). One study has suggested a protective role for thiopurines in this context (Beaugerie et al., 2009b) though these patients were not corrected for co-administration of 5ASA preparations which may also have a protective role in this setting.

There also appears to be an increased risk of certain non-colorectal malignancies amongst IBD patients. In the same cohort of patients from the CESAME study, prospective data suggested a 20-fold increased risk of small bowel adenocarcinoma and suggestion of an increased risk of skin and cervical malignancy (Beaugerie et al., 2009c). In a database of over 27,000 UC patients from Sweden, the standardised incidence ratio (SIR) for all cancers was 1.46 with increased risk of malignancy of the liver, small bowel (carcinoid), prostate and breast (Hemminki et al., 2008). In a recent review of malignancies associated with thiopurine therapy, Smith et al concluded that these drugs did not increase the risk of cervical dysplasia, colonic cancer or solid organ tumours in IBD patients (Smith et al., 2010). A retrospective cohort study of over 50,000 IBD patients from the US suggested an increased risk of non-melanomatous skin cancer and that this risk was highest in patients treated with thiopurines (Odds Ratio 4.27) and biological therapies (Odds Ratio 2.18) (Long et al., 2010).

Many of these studies have also shown an increased risk of lymphoma and this will be discussed further in this chapter.
