Cancer risk in patients with alopecia areata: a nationwide population‐based matched cohort study

Alopecia areata (AA) is an organ‐specific autoimmune disorder. Defective immune system related disorders are prone to increase the risk of cancer formation. However, the association among AA and variety of cancer types had never been studied. A nationwide population‐based matched cohort study was conducted to evaluate the cancer risk in patients with AA. Records from Taiwan National Health Insurance Research Database were analyzed. Cases of AA from 1997 to 2013 and cancers registered in the catastrophic illness profile from the same time period were collected. The standard incidence ratio (SIR) of each cancer was calculated. In total, 2099 cancers among 162,499 patients with AA and without prior cancers were identified. The overall cancer risks in AA patients were slightly decreased, especially among male subjects (SIR: 0.89). Refer to individual cancer, the cancer risk of nonmelanoma skin cancer (NMSC) (SIR: 0.59), upper GI cancer (SIR: 0.70), liver cancer (SIR: 0.82), uterine, and cervix cancer (SIR: 0.84) were significantly lower in patients with AA. In contrast, AA patients were inclined to have lymphoma, breast cancer, kidney, and urinary bladder cancer with the SIR of 1.55, 2.93, and 2.95, respectively. Age stratified analyses revealed female AA patients younger than 50 years old have even higher risk of breast cancer (SIR: 3.37). Further sensitivity analysis showed similar results after excluding major autoimmune disorders. Cancer risk in AA patients is organ specific, and it is not associated with the underlying autoimmune disorders in patients with AA.