Psoriasis is a chronic inflammatory disease that affects about 3% of the population. Over the past decade, more attention has been placed on the relationship between psoriasis and other medical comorbidities. Because of this, patients often wonder if there is an increased risk of malignancy in adults with psoriasis. Theoretically, there are several factors that may promote malignancies in patients with psoriasis. The persistent immune activation associated with psoriasis may promote a pro-malignancy state. Patients with psoriasis have higher rates of tobacco use, alcohol use, and obesity,1,2 which may increase their risk of developing certain types of malignancy.
Finally, some psoriasis treatments, including UV exposure from phototherapy and immunosuppressive medications, may put people at an increased risk of cancer. Because of this, it is important for dermatologists to understand the real-world relationship between psoriasis and malignancy. This article focuses on the baseline risk of malignancy, risks associated with treatments for psoriasis, and management strategies for patients with psoriasis and a history of malignancy.
Baseline Risk of Malignancy in Psoriasis
A meta-analysis of 6 studies found an increased risk in the development of any malignancy, excluding keratinocyte carcinomas, in psoriasis patients compared with the general population (standard incidence ratio [SIR], 1.16; 95% CI, 1.07-1.25); however, many of the studies included in this meta-analysis did not adjust for other malignancy risk factors, including smoking or alcohol use.3 Subsequently, a study using US-based claims data, with 5 years of follow-up, found a 20% increased rate of any malignancy, excluding keratinocyte carcinomas, in psoriasis patients, after controlling for age and sex, compared with the general population.4 The results of these 2 studies were confirmed by a population-based cohort study of patients in The Health Improvement Network (THIN), a primary care medical records database in the United Kingdom (UK). This study found a small, but significant risk of cancer in psoriasis patients compared with the general population, after controlling from age, body mass index, smoking, and alcohol use (hazard ratio [HR], 1.06; 95% CI 1.02-1.09).5
This increased risk of malignancy appears to be driven, in part, by increased rates of lymphoma. Several studies have confirmed an increased risk of lymphoproliferative malignancies in patients with psoriasis,4-7 with the strongest risk association between severe psoriasis and Hodgkin lymphoma.5,7 The data for other specific types of cancer is less robust and the results are conflicting. Additionally, multiple studies have confirmed an increased risk of keratinocyte carcinomas in patients with psoriasis, with the highest rates in patients with a history of phototherapy treatment.3-5 The data for melanoma, however, is conflicting. A meta-analysis failed to find a statistically significant increased risk, but the population-based cohort study from the UK did report an elevated risk of melanoma, after controlling for age and sex (HR, 1.15; 95% CI, 1.02-1.30).5
Skin Cancer Risk Associated With Phototherapy
There is a well-established link between oral psoralen–UV-A (PUVA) phototherapy, and cutaneous squamous cell carcinoma (SCC). This data comes from a prospective cohort of patients established by Stern and colleagues in 1975, treated with PUVA and subsequently followed for more than 30 years.8 The final paper was published with 30 years of follow-up and found a dose-response, increased risk of SCC in patients who received more than 150 treatments, and this risk persisted for at least 15 years after treatment cessation.9,10 About 7% of patients who received 200 PUVA treatments and more than 50% of patients who received at least 400 treatments developed at least 1 SCC during the follow-up period.10 Additionally, one-third of patients exposed to at least 200 treatments developed at least 1 basal cell carcinoma.10 A delayed risk of melanoma, beginning 15 years after starting PUVA treatment, was also seen in patients who received more than 200 PUVA treatments.11
While UV radiation is a well-documented risk factor for the development of skin cancer,12 there is little information, and no prospective studies, evaluating the use of therapeutic narrowband UV-B phototherapy and the development of keratinocyte carcinomas. A study of 1908 Scottish patients treated with narrowband UV-B who were followed for a median duration of 4 years found no increased risk of SCC or melanoma, but a small, but significant increase in basal cell carcinoma was detected (standardized rate ratio, 213; 95% CI, 102-391).13
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