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

Introduction: Studies have reported higher cancer risk in individuals with psoriasis, a chronic inflammatory autoimmune disease; however, adjustment for potential confounders was lacking.

Methods: 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).

Results: 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.

Conclusion: The observed association between psoriasis and colon cancer may reflect inflammatory or unidentified processes.