Psoriasis patients have a heightened risk of malignant lymphoma

LONDON - Patients with psoriasis are more likely than the general population to receive a diagnosis of malignant lymphoma, a large Danish study has found.

Malignant lymphomas are known to occur more frequently among patients with chronic inflammatory and autoimmune diseases, such as Sjögren's syndrome and rheumatoid arthritis, but whether the risk of lymphoma is greater in psoriasis has been a subject of controversy; some, but not all, studies have found an increased risk, and data from larger studies are limited.

Results from one of the largest studies to date, which quantifies the five-year risk of new-onset Hodgkin lymphoma (HL), non-Hodgkin lymphoma (NHL) [excluding cutaneous T-cell lymphoma (CTCL)] and cutaneous T-cell lymphoma (CTCL) in patients with psoriasis, were presented at the Psoriasis: From Gene to Clinic International Congress in London on Thursday 30th November.

The study included data on all patients aged ≥ 18 years who had been coded as having psoriasis between 2008 through 2012 or who were receiving treatment with a topical vitamin D derivative – the standard first line treatment for psoriasis in Denmark and which is not used to treatment any other conditions. A total of 58 138 patients with psoriasis were identified and their data were compared against 4 303 731 general population controls to determine incidence rates (IRs) per 10 000 person-years and calculate hazard ratios (HRs) using Cox regression analysis for Hodgkin lymphoma, non-Hodgkin lymphoma and cutaneous T-cell lymphoma.

The researchers found that incidence rates for Hodgkin lymphoma, non-Hodgkin lymphoma and cutaneous T-cell lymphoma were higher among patients with psoriasis compared with the general population; in Hodgkin lymphoma the incidence rate in psoriasis patients was 1.02 compared with 0.45 the general population (95% CI 0.70–1.47), in non-Hodgkin lymphoma it was 4.04 compared with 2.68 (95% CI 3.36–4.87) and in cutaneous T-cell lymphoma it was 0.44 compared with 0.10 (95% CI 0.25–0.77).

Calculation of adjusted hazard ratios revealed that there was a significant associations between psoriasis and Hodgkin lymphoma (1.50, 95% CI 1.01–2.23) but not non-Hodgkin lymphoma (1.02, 95% CI 0.84–1.24) or cutaneous T-cell lymphoma (1.66, 95% CI 0.88–3.13).

However, when patients were stratified by disease severity, with psoriasis patients receiving systemic therapy deemed to have severe disease and others categorised as having mild disease, adjusted hazard ratios were found to be significant for mild psoriasis and Hodgkin lymphoma (2.08, 95% CI 1.38–3.15), and for severe psoriasis and non-Hodgkin lymphoma (1.64, 95% CI 1.12–2.40) and cutaneous T-cell lymphoma (13.63, 95% CI 6.72–27.64).

Presenting the research at the congress, Maria Kamstrup, from the Department of Dermatology and Allergy, Herlev and Gentofte Hospital, Hellerup, Denmark said: “We found that patients with severe psoriasis have an increased risk of non-Hodgkin lymphoma, especially cutaneous T-cell lymphoma compared to the general population, and patients with mild psoriasis had a slightly increased risk of Hodgkin lymphoma compared to the general public.”

The high occurrence of cutaneous T-cell lymphoma associated with psoriasis seen has also been reported by other studies, she explained. A large population-based study using a general practice research database in the UK found an 11 fold increase risk of cutaneous T-cell lymphoma in severe psoriasis¹ and a Danish cohort study found a 15 fold increase risk of mycosis fungoides - the most common form of cutaneous T-cell lymphoma - in psoriasis patients discharge from the hospital, she said.

“A partial explanation for this might be that cutaneous T-cell lymphoma is misdiagnosed as psoriasis and can also be mistaken for atopic dermatitis due to similarities in the skin manifestation,” she explained, adding that non-specific histology findings on investigation often delay diagnosis of cutaneous T-cell lymphoma.

REFERENCES:

Psoriasis and risk of malignant lymphoma: a population-based cohort study. M. Kamstrup, L. Skov, C. Zachariae, J. Thyssen and A. Egeberg.  FC01. Psoriasis: From Gene to Clinic International Congress, London, Nov. 30, 2017. (page 56)

1. Gelfand JM, Shin DB, Neimann AL, Wang X, Margolis DJ, Troxel AB. The Risk of Lymphoma in Patients with Psoriasis. Journal of Investigative Dermatology 2006; 126 (10): 2194-2201.  https://doi.org/10.1038/sj.jid.5700410