Several large studies have explored the link between psoriasis and cancer, and two kinds of cancer have been implicated — squamous cell carcinoma in the skin and lymphoma, says Robert T. Brodell, MD, a professor of dermatology at the University of Mississippi Medical Center in Jackson.
Psoriasis and Squamous Cell Skin Cancer
“Several ‘big data’ studies have shown a slightly higher rate of skin cancer in patients with psoriasis,” says Dr. Brodell. These are studies that look at large groups of people to find out the frequency of certain conditions in different groups of people.
Although these types of studies can be informative, they show an association, not causation, and some relationships show up simply by chance, Brodell says. Still, people with psoriasis have been shown to have an increased risk for squamous cell cancer in most of these kinds of studies.
Squamous cell cancer is a type of skin cancer that starts in the squamous cells, which make up the middle and outer layers of the skin. It’s usually not life-threatening, but if it goes untreated it can grow large and spread to other parts of the body.
But it may not be the psoriasis or the inflammation that comes with it causing the increased risk.
“Almost all patients with psoriasis come to find out that exposure to the sun and ‘tanning’ help to control their psoriasis, and there is no question that sun exposure increases the risk of skin cancer, including squamous cell carcinoma,” says Brodell.
People with psoriasis who have spent more time in the sun may have increased rates of skin cancer for this reason, he adds.
Psoriasis and Lymphoma
Evidence suggests that psoriasis may be associated with a higher risk of lymphoma, a cancer of the immune system, says Joel M. Gelfand, MD, a professor of dermatology and of epidemiology at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia.
“The association of psoriasis and lymphoma is strongest for cutaneous T-cell lymphoma, a type of lymphoma of the skin,” says Dr. Gelfand. But the risk of lymphoma in people with psoriasis is still quite low, so they shouldn’t be alarmed, he adds.
Cutaneous T-cell lymphoma is a rare type of cancer that begins in white blood cells known as T cells or T lymphocytes. These cells help the body’s germ-fighting immune system, but in cutaneous T-cell lymphoma, the T cells attack the skin.
“If psoriasis is not responding appropriately to treatment, then a simple skin biopsy may be necessary. Additional symptoms of lymphoma include swollen glands, weight loss, fatigue, and night sweats,” says Gelfand.
Patients with these symptoms, particularly if they are persistent for weeks or months should see their medical provider, he says.
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