What kind of cancer is associated with Crohn's disease?

Colorectal Cancer is the Primary Malignancy Associated with Crohn's Disease

Patients with Crohn's disease involving the colon (Crohn's colitis) have an approximately 2-fold increased risk of developing colorectal cancer (CRC) compared to the general population, with the risk being roughly equivalent to that seen in ulcerative colitis. 1

Primary Cancer Risk: Colorectal Adenocarcinoma

The most well-established malignancy associated with Crohn's disease is colorectal adenocarcinoma, particularly when the disease involves the colon. 1

Magnitude of Risk

• The standardized incidence ratio for CRC in Crohn's disease ranges from 1.9 to 2.5, with a relative risk of approximately 4.5 in some meta-analyses. 1
• Cumulative cancer risk is approximately 1% at 10 years, 2% at 20 years, and 5% after more than 20 years of disease duration. 1
• The annual incidence is estimated at 0.06-0.20%. 1

Key Risk Factors for CRC Development

The following factors substantially increase cancer risk in Crohn's disease patients:

• Extensive colonic involvement: Risk is highest with pancolitis, intermediate with left-sided colitis, and minimal with isolated proctitis. 1
• Disease duration: Risk increases significantly after 8-10 years of colonic inflammation. 1
• Younger age at diagnosis: Patients diagnosed before age 30 have a standardized incidence ratio of 7.2. 1
• Primary sclerosing cholangitis (PSC): Concomitant PSC increases CRC risk 4-fold compared to Crohn's disease patients without PSC. 1
• Family history of CRC: First-degree relative with CRC doubles the risk. 1, 2
• Severity and duration of inflammation: Chronic, severe mucosal inflammation significantly elevates risk. 1

Unique Characteristics of Crohn's-Associated CRC

Colorectal cancers arising in Crohn's disease have distinct features compared to sporadic CRC:

• More advanced stage at diagnosis: Higher frequency of Duke's C (31% vs 27%) and D stage tumors (23% vs 21%). 1
• Higher histological grade: More often mucinous or signet-ring cell histology. 1
• Younger age at cancer diagnosis: Approximately 7 years younger than non-IBD CRC patients. 1
• Multifocal dysplasia: Field cancerization effect increases risk of synchronous lesions. 1

Secondary Malignancies Associated with Crohn's Disease

Small Bowel Adenocarcinoma

Crohn's disease increases the risk of small intestinal adenocarcinoma, though the absolute risk remains low. 1, 3, 4 This is particularly relevant given that small bowel involvement is common in Crohn's disease.

Anal Squamous Cell Carcinoma

Patients with Crohn's disease and chronic perianal fistulizing disease have an elevated risk of anal cancer:

• Incidence of 2.6 per 10,000 person-years in patients with perianal lesions versus 0.8 per 10,000 person-years without. 1
• Combined incidence of anal squamous cell carcinoma and adenocarcinoma is 3.8 per 10,000 person-years with long-standing perianal disease. 1
• Human papillomavirus infection is an additional risk factor. 1

Cholangiocarcinoma

Cholangiocarcinoma risk is increased 4-fold in IBD patients, predominantly driven by concomitant PSC, which increases risk more than 150-fold (5-10% lifetime risk). 1

Lymphoma

While some studies suggest increased lymphoma risk in Crohn's disease, this appears more related to immunosuppressive therapy (particularly thiopurines) rather than the disease itself. 3, 4

Clinical Surveillance Implications

For Crohn's colitis patients, colonoscopic surveillance should begin after 8 years of disease to assess extent and initiate cancer screening. 1

High-Risk Groups Requiring Intensive Surveillance

The following patients warrant annual colonoscopy:

• Concomitant PSC (from time of PSC diagnosis, continuing even after liver transplantation). 1
• Extensive colitis (pancolitis). 1
• Family history of CRC in first-degree relative. 1, 2
• Colonic strictures or bypassed segments. 1, 5

Important Caveats

• Rectal stump cancer: Patients with diverted rectal segments remain at risk and require surveillance. 5
• Delayed diagnosis: CRC detection may be delayed in Crohn's disease due to overlapping symptoms with active inflammation, often resulting in more advanced stage at diagnosis. 4, 5
• Strictures are concerning: Any colonic stricture in long-standing Crohn's colitis should be considered malignant until proven otherwise; strictureplasty is contraindicated in this setting. 1