Association between psoriasis and incident cancer: the Iowa's Women's Health Study

Studies have reported higher cancer risk in individuals with psoriasis, a chronic inflammatory autoimmune disease; however, adjustment for potential confounders was lacking. We examined the association of psoriasis with cancer incidence in 32,910 women after age 65 in the IWHS cohort linked to Medicare. Psoriasis was defined as: 2+ psoriasis claims from any Medicare file during 1991-2004 or 1+ psoriasis claim from a dermatologist (n = 719). Severe psoriasis was defined as 4+ psoriasis claims from a dermatologist in any year (n = 121). Cox proportional hazards regression, with psoriasis as a time-dependent variable was conducted to calculate hazard ratios (HR) and 95% confidence intervals (CI) of total (n = 6,488), breast (n = 2,066), lung (n = 742), and colon cancers (n = 947). With age-adjustment, psoriasis (yes vs. no) was associated with increased risk of lung 1.9 (95% CI: 1.2-3.0), colon 1.6 (95% CI: 1.1-2.5), and total cancer 1.2 (95% CI, 1.0-1.4). After further adjustment for smoking, body mass index, education, physical activity, and hormone therapy use, only the association for colon cancer remained statistically significant (HR = 1.6, 95% CI: 1.0-2.4) and was stronger for severe psoriasis. The observed association between psoriasis and colon cancer may reflect inflammatory or unidentified processes.