A new study published in February 2020 in the journal JAMA Dermatology reports that there is a 21% increased risk of cancer in patients with psoriasis, but not with psoriatic arthritis alone.
What is psoriasis?
Psoriasis is a chronic inflammatory disease that affects the skin and the joints, mediated by the T immune cells. The skin cells typically travel from the basal layer of the epidermis, where they are generated to the most superficial layer. By the time they reach the top layer, they have differentiated completely and are dead skin cells or keratinocytes, filled with the skin protein called keratin.
However, in psoriasis, the basal cells speed up on their journey to the top layer, and as a result, they reach it in an immature state, pushing the mature keratinocytes off. The skin, therefore, appears red, tender, cracked, and peeling.
Earlier studies have found that patients with psoriasis are at an increased risk of cancer compared to people without the condition or the general population. Psoriasis is also associated with smoking and drinking; two factors also linked to cancer risk. It is already known that lymphomas and keratinocyte cancers are present at a higher rate in patients with psoriasis.
Psoriasis on elbow. Closeup. Image Credit: Hriana / Shutterstock
Secondly, several new biologic drugs have been introduced for the treatment of psoriasis, but biologic agents have a risk of cancer. However, whether these agents confer a risk of cancer independent of the disease itself is an unanswered question.
The current study is a systematic review and meta-analysis to find the risk of cancer in two conditions, namely, psoriasis and psoriatic arthritis, in addition to the risk of specific cancers. The researchers also aimed at finding the risk of cancer in psoriasis patients who are on biologic agents rather than conventional drugs.
The researchers looked at 112 studies in which over 2 million patients with psoriasis or psoriatic arthritis were involved, and in which cancer outcomes were reported. They analyzed the risk of cancer overall, and certain cancers specifically.
The study showed an almost 4.8% prevalence of cancer in psoriasis patients, with an incidence rate (IR) of nearly 11.8 per 1000 person-years. If keratinocyte cancer is excluded, the prevalence and IR are 4% and 7.6, respectively.
Eight studies showed a higher and two studies at a lower risk of cancer in psoriasis patients. The overall risk was 20% higher, or 14% higher after excluding keratinocyte cancer.
Keratinocyte cancer occurred in 2.5% of patients with psoriasis, with an IR of 4.4. The risk for this cancer was more than 2.28 times higher in psoriasis patients compared to others. For melanoma, lymphoma, and non-Hodgkin lymphoma, the risk was 13%, 56%, and 48% higher, respectively. For Hodgkin lymphoma, the risk was 87% higher.
Concerning breast cancer and colorectal cancer, the risk was not higher in these patients. However, psoriasis patients were at a 26% higher risk of lung cancer.
Overall, there was no significant change in the risk of cancer for patients on biological agents, nor when keratinocyte cancer or lymphomas were considered. The same was the case with psoriatic arthritis as well, except for breast cancer, which was significantly higher in three studies.
The current study includes over twice the number of studies as the last comprehensive review in 2013, including newer studies with a more significant number of participants. Yet the findings remain the same overall, supporting the existence of an association between psoriasis and cancer, but not psoriatic arthritis.
Keratinocyte cancer is linked to sunlight exposure, and the risk is significantly increased in patients with psoriasis who are on PUVA therapy, involving exposure to ultraviolet rays. The highest risk is for squamous cell carcinoma. Other factors that have been suggested are more extended periods spent in the sunlight and treatment with UVB irradiation and with coaltar, which are both risk factors for keratinocyte cancer.
The increased risk of lymphoma may be due to the higher risk of cutaneous T-cell lymphoma, which is markedly more common in people with severe psoriasis. This might be due to chronic activation of the immune system, the authors speculate.
Lifestyle factors like alcohol and smoking are also linked to the higher risk of psoriasis and also of cancer in these patients. However, other factors are also involved, and these need to be identified.
With many different types of cancer occurring at a higher rate in patients with psoriasis, it is essential that doctors who treat such patients be aware that such risks exist. Especially in the case of lymphomas, any therapy for psoriasis which activates the immune system could also result in increased lymphoma activity. More research is required to assess the risk with the use of biologic agents and in psoriatic arthritis.
Vaengebjerg S, Skov L, Egeberg A, Loft ND. Prevalence, Incidence, and Risk of Cancer in Patients With Psoriasis and Psoriatic Arthritis: A Systematic Review and Meta-analysis. JAMA Dermatol. Published online February 19, 2020. doi:10.1001/jamadermatol.2020.0024