Data indicate that psoriasis is one of the most common immune-mediated disorders, affecting approximately 0.5% to 11.4% of adults worldwide and significantly impacting patient’s quality of life. Other research suggests that colorectal cancer (CRC) is one of the leading causes of cancer-related mortality and the fourth most commonly diagnosed cancer in both men and women worldwide (900,000 deaths and 1.8 million new cases annually according to the WHO). With psoriasis and CRC both related to immune-mediated chronic inflammation and interleukin-17 shown to be involved in the pathogenesis of psoriasis and initiation of CRC, it has been hypothesized that patients with psoriasis are at increased risk for comorbid CRC. However, the relationship between the two conditions remains unclear.

A Systematic Review & Meta-analysis

To appraise the evidence on the relationship between psoriasis and CRC, Ching-Chi Chi, MD, MMS, DPhil, FAAD, and colleagues conducted a systematic review and meta-analysis of observational studies that examined this association, publishing their results in the Journal of the American Academy of Dermatology. “We searched MEDLINE and Embase on March 24, 2020 for relevant studies,” explains Dr. Chi. Included studies provided data on the risk for CRC and had a case group of patients with psoriasis and a control group of patients without psoriasis. Nine cohort studies with more than 10.5 million subjects were included.

“The Newcastle-Ottawa scale was used to evaluate the risk of bias of included studies, and we conducted random-effects model meta-analysis and subgroup analysis based on gender,” notes Dr. Chi. When relevant data were available, the study team conducted meta-analysis on the risk for colon cancer and rectal cancer, as CRC is composed of both. Meta-analyses were only conducted when there were at least three included studies for a given outcome, with the researchers applying the random-effects model due to the expectation of clinical heterogeneity across the included studies.

Significantly Increased Colorectal Cancer Risk

Eight studies that provided data for the meta-analysis demonstrated an increased risk for CRC in patients with psoriasis (Table). “We found a significantly increased risk for CRC in patients with psoriasis upon meta-analysis, with patients with psoriasis having a 16% greater risk for CRC than the general population,” says Dr. Chi. “Subgroup analysis for rectal and colon cancer provided similar results.” Five studies providing data on risk for colon cancer found significantly increased risks among patients with psoriasis when compared with controls (HR, 1.14; 95% CI, 1.05-1.24). Three studies reporting data on rectal cancer risk found an increased, but not significantly increased, risk among patients with psoriasis when compared with controls (HR, 1.18; 95% CI, 0.99-1.41). No statistical heterogeneity was seen across the eight, five, or three studies in each of these meta-analyses.

“Subgroups analysis based on gender found significantly increased risk for CRC in female patients with psoriasis across five included studies (HR, 1.41; 95% CI, 1.16-1.72) but not in male patients with psoriasis across five included studies (HR, 1.18; 95% CI, 0.92-1.50),” notes Dr. Chi.  

Looking Ahead

While the cohort studies in the meta-analysis and other reviews indicate that patients with psoriasis have an increased risk for colorectal cancer, “the pathogenesis between psoriasis and CRC remains ambiguous,” says Dr. Chi. “More studies are warranted to confirm if psoriasis and CRC share genetic susceptibility, molecular defect and microbiota imbalance.” In the meantime—with patients with early stage colorectal cancer initially exhibiting no symptoms, the possible fatal risk of late-stage colorectal cancer, and evidence that early CRC diagnosis improves survival—he suggests that gastroenterology consultation and detailed colonoscopy examination are indicated for patients with psoriasis who present with bowel symptoms.