SCOTTSDALE, ARIZ. – Psoriasis of all severities was linked to a 3.5-fold increase in risk of cutaneous T-cell lymphoma, and severe psoriasis upped the associated risk of Hodgkin lymphoma by about 2.5 times, in a large, longitudinal, population-based cohort study.
Psoriasis also was tied to a smaller but statistically significant increase in the risk of non-Hodgkin lymphoma, said Zelma Chiesa Fuxench, MD, of the department of dermatology, the University of Pennsylvania, Philadelphia. Overall, lymphoma risk was highest in people with severe psoriasis, independent of traditional risk factors and exposure to immunosuppressive medications, Dr. Fuxench said at the annual meeting of the Society for Investigative Dermatology.
Psoriasis affects more than 125 million people worldwide, and severe cases are a major cause of cancer-related mortality. “Prior studies have suggested an increased risk of lymphoma in psoriasis patients, but it is unclear if this due to chronic inflammation, exposure to immunosuppressive therapies, or a combination of both factors,” Dr. Fuxench said.
To further explore these links, she and her associates analyzed electronic medical records from THIN (The Health Information Network), which includes about 12 million patients across the United Kingdom. Adults with psoriasis were matched to up to five nonpsoriatic controls based on date and clinic location. Patients who needed systemic medications or phototherapy were categorized as having severe psoriasis. The final dataset included more than 12,000 such patients, as well as 184,000 patients with mild psoriasis and more than 965,000 patients without psoriasis.
Psoriasis patients were younger and more likely to be overweight, male, and smoke and drink alcohol than patients without psoriasis, Dr. Fuxench said. Almost 80% of patients with severe disease had received systemic therapies, most often methotrexate (70% of systemic treatments) or cyclosporine (10%), while only 1% had received biologics.
Patients with severe psoriasis were more likely to be diagnosed with Hodgkin disease, non-Hodgkin lymphoma, and cutaneous T-cell lymphoma than were patients with mild psoriasis or controls. Over a median follow-up of 5.3 years, 34 patients with severe psoriasis were diagnosed with any type of lymphoma, for an incidence of 5.2 cases per 10,000 person-years (95% confidence interval, 3.7-7.3). In contrast, incidence rates for patients with mild psoriasis and controls were 3.3 and 3.2 cases per 10,000 person-years, respectively, Dr. Fuxench said.
In the multivariable analysis, patients with psoriasis were about 18% more likely to develop any type of lymphoma than were controls, an association that reached statistical significance (adjusted hazard ratio, 1.18; 95% CI, 1.06-1.31). Mild psoriasis increased lymphoma risk by 14%, and severe psoriasis upped it by about 83%, and both associations were statistically significant.
The increase in risk of non-Hodgkin lymphoma was 13% greater with mild psoriasis and 56% greater with severe disease, compared with controls, and these associations also reached statistical significance. Mild psoriasis was not linked to Hodgkin lymphoma, but patients with severe psoriasis were about 250% more likely to develop it than controls, with a trend toward statistical significance (aHR, 2.54; 95% CI, 0.94-6.87).
Finally, severe psoriasis was linked to a more than ninefold increase in risk of cutaneous T-cell lymphoma (aHR, 9.3; 95% CI, 4.1-21.4), while mild psoriasis was linked to about a threefold increase in risk.
“These results were robust in multiple sensitivity analyses, including analyses that excluded patients with rheumatoid arthritis, psoriatic arthritis, or a history of exposure to methotrexate, cyclosporine, or biologics,” Dr. Fuxench said. Future studies should explore the effect of treatment timing and selection on cancer risk, she added. “For those of us who care for these patients, we are increasingly using systemic agents that selectively target the immune system, and these questions will arise in clinics.”
The study’s design made it possible to pinpoint dates of diagnosis more effectively than investigators could estimate disease duration or confirm whether patients initially diagnosed with psoriasis actually had cutaneous T-cell lymphoma, Dr. Fuxench noted. “Ideally, we could have another cohort study of incident psoriasis with prospective follow-up, but lymphoma is so rare that there is currently not enough power [in the THIN database] to determine associations.”
The study was funded by grants from the National Institutes of Health and the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Dr. Fuxench disclosed unrestricted research funding from Pfizer outside the submitted work.