Introduction
Many transplant patients don’t realize that immune suppression drugs used to prevent rejection are placing them at higher risk for cancer. The National Kidney Foundation (NKF) recently conducted a survey to assess what kidney transplant patients knew about their higher risk for cancer. The preliminary results were presented at the 2006 World Transplant Congress meeting in Boston as an abstract and oral presentation. It was reported that of the 584 patients that responded to the NKF survey, about 25% said they learned about the cancer risk only after the surgery. Two-thirds of the respondents said they wanted more information about their risk.
Role of the Immune System
The body has a complex system of recognizing its own cells and attacking foreign invaders. Key to this system is the use specific markers (human leukocyte antigens) on cells that uniquely identify them as our own. If the immune system finds something lacking these markers or have different markers, there will be an attack and an attempt to destroy them.
Immune System and Transplantation
Unless a transplanted organ comes from identical twin, it is going to have different cell markers than those of the person who receives it. This means that the recipient’s immune system will treat the transplanted organ as a foreign object to be destroyed (or rejected). Since most transplants don’t involve identical twins, powerful drugs are needed to suppress the immune system enough to prevent rejection but not so much that the body is left undefended against foreign invaders (bacteria, viruses, parasites, fungi).
Immune System and Cancer
Although the immune system is constantly on the look out for foreign invaders, sometimes it can recognize abnormal cells that are precursors to cancer. Although the immune system is not as effective against cancer as it is against foreign invaders, it does protect us to a degree. When the immune system is weakened (for whatever reason), there is a higher risk of getting cancer.
Getting Cancer After Tranplantation
People who have undergone solid organ (kidney, liver, heart, etc) transplantation and are taking immune suppressing drugs are at a higher risk of getting cancer. In fact, the third leading cause of death among long term solid organ transplant survivors is cancer. Overall there is a three- to four-fold risk of developing cancer compared to the general population. The highest risk is for skin cancer and certain types of lymphoma but there is a higher risk for many other cancers as well. Unfortunately, cancer arising in transplant patients tends to be more aggressive than those found in the general population. The average age of diagnosis is 40 years old and many can occur within in the first few years after the transplant. Risk for certain types of lymphoma is particularly high during the first year and after treatment for rejection because this is when the immune system is most suppressed.
Risk Factors for Cancer
One of the most important risk factors for post-transplant cancer is the intensity and duration of the immune system suppression. For example, heart transplant patients receive higher levels of immunosuppression than kidney transplant patients, so they are at higher risk. Because skin cancer is the number one cause of cancer in transplant patients, excessive exposure to UV is an important risk factor. Other risks include certain viral infections (EBV) and in the case of kidney failure patients, how long they have been on dialysis.
Close Follow-up and Screening
Transplant patients need to be followed closely and to receive periodic screening for cancer. In addition to basic cancer screening, it is critical that there be a monthly skin exam and a yearly evaluation by a dermatologist. Those at higher risk for skin cancer should be seen more frequently. Unfortunately, less than 15% of transplant patients visit a dermatologist for routine screening.
Prevention / Treatment
The most important methods for preventing cancer after a transplant is careful screening (donor and patient) before starting immunosuppressive drugs and avoiding excessive immune suppression. Because of the high risk of skin cancer, exposure to UV radiation should be severely restricted. Some types of cancers may respond to decreasing or stopping the immune suppression, but many do not. If a cancer does not initially respond to a decrease or change in drugs, chemotherapy and other treatments will likely be needed.
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