The results are in line with earlier studies, and the current review found a link with bladder cancer and lung cancer.
Patients with psoriasis appear to have a slightly increased risk of cancer, particularly keratinocyte cancer and lymphomas, according to a systematic review and meta-analysis published in JAMA Dermatology.
However, psoriatic arthritis was not associated with an increased risk.
Overall, the review found that the prevalence of cancer in patients with psoriasis was 4.78% (95% CI, 4.02%-5.59%), with an incidence rate (IR) of 11.75 per 1000 person-years and a risk ratio (RR) of 1.21.
As with a similar meta-analysis published in 2013, this review, which examined 112 studies, showed a similar link between psoriasis and cancer. The 2013 study found an association between psoriasis and cancer excluding keratinocyte cancer, keratinocyte cancer, and some solid cancers, including respiratory tract and urinary tract cancer. Besides the link with skin-related cancer, the current study found a link with bladder cancer and lung cancer. The authors noted that their analysis is larger, with twice as many studies, newer trials, and over 2 million patients. “Given that our results align with those of the older analysis, the notion of an association is supported,” the authors wrote.
The cancers with the highest apparent risk for patients with psoriasis are keratinocyte cancer (RR, 2.28; CI, 1.73-3.01), lymphomas (RR, 1.56; 95% CI, 1.37-1.78), lung cancer (RR, 1.26; 95% CI, 1.13-1.40), and bladder cancer (RR, 1.12; 95% CI, 1.04-1.19).
There was no increased risk found for patients with psoriasis who are treated with biologic agents.
The overall prevalence of keratinocyte cancer in patients with psoriasis was 2.55%, with an IR of 4.35 and an RR of 2.28. Results could be explained by patients with psoriasis having a high exposure to sunlight and psoralen-UV-A (PUVA) treatments. Many patients with psoriasis often spend more time in the sun and have been treated with UV-B irradiation and tar, 2 factors known to increase the risk of developing keratinocyte cancer.
However, a previous study from Denmark that adjusted for cofounders, including PUVA treatments, still found a small but significant increased risk, indicating that other factors may play a role. The authors note that, “Patients with psoriasis see dermatologists more frequently than the general population and therefore, more keratinocyte cancers may be detected.”
Prevalence for developing all types of lymphomas was found to be 0.25%, with an IR of 0.39 and an RR of 1.56. There was a significantly higher prevalence for developing non-Hodgkin lymphoma (0.30.%) than for Hodgkin lymphoma (0.04%). The differences in IR and RR came at 0.35 and 1.48 for non-Hodgkin lymphoma and 0.35 and 1.87 for Hodgkin lymphoma.
Elevation in risk for lymphoma in part can be explained by an increased risk of cutaneous T-cell lymphoma (CTCL) in patients with psoriasis. Four of the reviews included studies did a separate analysis on CTCL and non-Hodgkin lymphoma excluding CTCL, all of which found the risk of CTCL to be highly increased for patients with severe psoriasis. Another explanation is that persistent immune activation in these patients could lead to the development of a dominant T-cell clone.
Certain lifestyle factors, like smoking and alcohol consumption often associated with patients with psoriasis, may also contribute to increased cancer risk, according to several studies. For example, Brouchli et al found an increased risk of cancer (excluding keratinocyte cancer) when adjusting for body mass index (BMI), smoking, and benign tumors.
“Given that the effect sizes diminish when adjusting for certain lifestyle factors, it is evident that these lifestyle factors are associated with the increased risk of cancer observed in patients with psoriasis,” the authors wrote, noting, however, that lifestyle factors cannot fully explain the link because the risk persist even after accounting for them.
The authors urge more doctors to be aware of increased cancer risks for their patients with psoriasis, “especially for lymphomas, as immunogenic treatment might be associated with exacerbations.”
The review stresses that evidence on increased risk for psoriatic arthritis is limited and further studies should be conducted.
Vaengebjerg S, Scov L, Egeberg A, Loft ND. Prevalence, incidence, and risk of cancer in patients with psoriasis and psoriatic arthritis [published online February 19, 2020]. JAMA Dermatol. doi: 10.1001/jamadermatol.2020.0024.