In lab tests of cultured cells, they found that a drug used by transplant recipients called azathioprine made cells more sensitive to UVA light. The researchers did not perform their tests on humans.
However, studies have found that a type of skin cancer called squamous cell carcinoma is 50 to 250 times more common among transplant patients. "Twenty years after transplant, between 60% and 90% of patients are affected," write Peter Karran, PhD, and colleagues in Science.
Karran works at Clare Hall Laboratories, which is part of Cancer Research U.K.'s London Research Institute.
About Squamous Cell Carcinomas
They often appear on parts of the body that get sun exposure, including the face, ear, neck, lip, and the back of the hands, says the ACS.
That's also true for organ transplant patients, note Karran's team. "Sunlight plus the duration of treatment with immunosuppressive drugs are acknowledged risk factors" for squamous cell carcinomas, the researchers write.
Sunlight consists of two types of harmful rays -- UVA rays and UVB rays. The UVB rays are the sun's burning rays and are the primary cause of sunburn and skin cancer. UVA rays penetrate deeper layers of the skin. These rays also contribute to sunburns and skin cancer.
According to the American Academy of Dermatology, both UVA and UVB rays can cause suppression of the immune system, which helps to protect against the development and spread of skin cancer.
Azathioprine has been commonly used to suppress the immune systems of organ transplant recipients, write Karran and colleagues.
The researchers found that a form of azathioprine built up in the DNA of the cells they tested. That buildup apparently led to increased sensitivity to UVA light, paving the way for DNA changes that could lead to cancer.
"These findings may partly explain the prevalence of skin cancer in long-term survivors of organ transplantation," the researchers write.
Karran's team doesn't make any recommendations about the use of azathioprine.