TUESDAY, Nov. 1 (HealthDay News) -- Organ transplant recipients in the United States double their risk of developing cancer compared to the general population. And that risk is elevated for 32 different types of cancer, according to new research.

In any given year, however, the risk of developing cancer after a transplant is just 0.7 percent. And experts say the benefits of transplantation far outweigh such risk.

"People need to understand that transplantation is one of the great success stories of medicine. It's a very effective treatment for people with severe organ disease," explained the study's lead author, Dr. Eric Engels, a senior investigator in the infections and epidemiology branch of the division of cancer epidemiology and genetics at the U.S. National Cancer Institute in Rockville, Md.

"Our study is saying that this population has a unique pattern of cancer risk. Transplant recipients need to be carefully screened and followed," Engels added.

Results of the study are published in the Nov. 2 issue of the Journal of the American Medical Association.

In 2010, almost 30,000 solid-organ transplants were performed in the United States, according to background information in the article. Kidney transplants accounted for more than half of that total, followed by livers, hearts and lungs.

After transplant, the recipient must take powerful immune system-suppressing medications to prevent the new organ from being rejected.

But those medications put transplant recipients in a catch-22 situation, said Dr. Darla Granger, director of the pancreatic transplantation program at St. John Hospital and Medical Center in Detroit. "Suppressing the immune system does increase the risk of cancer. And, if you have cancer, you want a strong immune system to fight the cancer," she added.

Another issue with the immunosuppressants is cancers that are related to viruses. For example, non-Hodgkin and Hodgkin lymphomas are linked to the Epstein-Barr virus, while cervical and several other types of cancers are caused by the human papillomavirus, and some liver cancers are caused by hepatitis B or C viruses.

"We've always known that certain tumors are increased after transplantation. Certain tumors are known to be related to viruses, so when we give immunosuppressant drugs, we're decreasing the body's ability to fight off viruses," explained Dr. Lewis Teperman, chief of transplant surgery at NYU Langone Medical Center in New York City.

Not all of the cancers can be linked to immunosuppression, however. In some cases, especially with liver and lung cancers, it's possible that a tiny cancer was present in the body before transplant.

"It's hard to sort out the exact cause of cancer, but some are clearly related to being immunosuppressed," Granger said.

Engels' study reviewed data from nearly 176,000 solid organ transplants done between 1987 and 2008.

The investigators found the overall incidence of cancer was 2.1 times higher than would be expected in a non-transplant population.

The risk of non-Hodgkin lymphoma was increased more than sevenfold. The rates of lung and liver cancer were also significantly increased, but Engels said this may be due to previous cancers. For example, a treatment for some liver cancers is a liver transplant, and it's possible that some cancer cells may survive the transplant process. The risk of lung cancer was highest in those who received a lung transplant, and the risk of liver cancer appeared to be elevated only in those who received a liver transplant.

The incidence of kidney cancer was increased in all transplant recipients by almost five times, according to the study. The researchers said this might be due to the underlying disease process in people who need new kidneys, and that the immunosuppressants likely play a role for all transplant patients.

"This study raises some very good points. It suggests that screening for viruses should be done, and that we should always be trying to use less immunosuppressants. It also raises the inclination to screen transplant recipients for tumors," Teperman said.

"This is an important paper, but I think it may overstate the risk. I think the risk of cancer is elevated, but it's probably less than seen here," he added.

For someone who's had a transplant or is waiting for one, Granger noted, "decrease the risk factors you can. Don't smoke. Follow good health practices. Wear sunscreen. And, if you've had a transplant, get the screenings your doctor recommends."

More information

Learn more about post-transplant cancer from the United Network for Organ Sharing (UNOS).