Psoriasis is a common condition of the skin resulting in redness, scaling, and itching. Sometimes it can be so severe that it prevents people from enjoying simple daily activities.

In difficult cases of psoriasis, powerful treatments are necessary to keep the disease under control. But those treatments have consequences. Among them is an increased risk of developing squamous cell cancers of the skin.

Squamous cell cancers are the most common form of skin cancer. For many years, a type of treatment using light, called PUVA, has been used to treat severe cases of psoriasis.

More recently, patients with severe psoriasis have been given a drug called cyclosporine, which is used most often in patients with organ transplants to prevent transplant rejection. This drug, which suppresses the body's immune system, is known to increase the risk of cancers in transplant patients.

What happens when cyclosporine is given to patients with psoriasis, whose prior treatments, such as PUVA, are known to also cause cancer? Could it make a difficult situation even worse by increasing even further the risk that the psoriasis patients already face?

The answer is yes. Psoriasis patients using cyclosporine have a dramatic increase in the number of squamous cell cancers of the skin.

In a study reported in The Lancet, (Vol. 358, No. 9287: 1042-1045), Isabelle Marcil, MD, and Robert Stern, MD, from the department of dermatology at Beth Israel Deaconess Medical Center in Boston, Mass., followed 1,380 patients who had received PUVA therapy from 1975 through 1976. A total of 844 patients were available to be part of the present study. Of that group, 31 patients had received cyclosporine treatment between 1975 and 1998.

When the researchers compared the psoriasis patients who received cyclosporine to those who did not, they found that any use of cyclosporine increased the risk of developing squamous cell skin cancer about three times. If the drug was taken for more than three months the risk was increased four times.

If a patient had received over 200 PUVA treatments in addition to cyclosporine the risk was nine times that of individuals who had received less than 200 PUVA treatments and no cyclosporine.

Compared to people without psoriasis, patients with psoriasis who took cyclosporine for more than three months and had PUVA treatment had an incidence of squamous cell skin cancer that was more than 100 times the general population.

According to the authors, there is apparently a significant increased risk for developing skin cancers with some medications given to patients with psoriasis — if those patients have previously been exposed to potentially cancer-causing agents.

In this study, the risk was increased primarily in those patients who had received over 200 PUVA treatments in addition to cyclosporine. Prior treatment with methotrexate, another drug commonly used in treating more advanced psoriasis, did not have the same effect.

The authors conclude, "In view of the magnitude of risk we recorded with restricted use of cyclosporine, we believe it prudent to assess carefully the carcinogenic potential of other immunosuppressive treatments for patients with severe psoriasis. Only then can the long-term safety of these agents for this chronic disease be established."

As always, the authors remind us, the risk of the treatment must be balanced against the effectiveness of the drug, as well as possibly the consideration of newer immunosuppressive drugs.