The most comprehensive study ever on the link between organ donations and cancer is arming physicians with new data that could help make the procedures safer.
Organ transplant patients get new kidneys, livers and lungs that save their lives, but they face a heightened risk of cancer because drugs that prevent the rejection of new organs also weaken the immune system.
Most patients, like Jessica Protasio of Columbia, go through with transplants because the immediate risk of dying from failing organs outweighs the long-term risk of cancer.
"My option at the time was to live or die," said Protasio, who received a liver transplant in March at the University of Maryland Medical Center.
But the research from the National Cancer Institute in Rockville could lead to safer medications and procedures.
The study looked at more than 175,000 transplant patients and found they were twice as likely to get cancer as the general population. Researchers found more than 30 cancers that were more common in transplant patients than in the rest of the population.
"One of our goals is to understand why cancer develops and increase our knowledge of what causes it to occur so that we can make transplant safer," said Eric A. Engels, the lead researcher on the study.
Past studies, more narrowly defined and smaller in size, probably didn't account as accurately for less common cancers. They might look at one group of patients, such as kidney transplant patients, and have far fewer examples. Most of the studies look at kidney transplants, which are the most common.
The NCI study, published in the Journal of the American Medical Association, used data from the Scientific Registry of Transplant Recipients, which tracks every organ transplant in the country. Researchers compared the information to 13 state databases that tracked cancer cases.
"This quantifies it better, which is really important," said Dr. Dorry Segev, the director of clinical research and transplant surgery at the Johns Hopkins School of Medicine, who has seen the study. "This opens the door for a lot of important questions to be answered with regards to who the patients are that are at risk and when the risk seems to emerge so we can do screening then."
The NCI study reinforced much of what had been found in smaller studies. Transplant patients are most likely to get cancers caused by viruses, which are able to break through the body's weakened immune system.
The most common cancers were non-Hodgkin lymphoma, which affects the immune system, and cancers of the lung, liver and kidney. These cancers made up 43 percent of all cancers in organ transplant patients, compared with 21 percent in the general population.
Doctors don't want to scare patients away from transplants, but use the research to better treat patients.
"It's not so common it means people should not get transplants," Engels said. "In the great majority of cases people never get cancer."
Engels said there are many theories about why cancer risk increases for transplant recipients.
The most common issue is the drugs that weaken the immune system, also seen in HIV patients. Studies have shown that HIV patients are two to 10 times more likely to get some cancers.
But from simply looking at the databases, Engels and the other researchers couldn't tell whether other factors contributed. Perhaps the very disease that created the need for a transplant predisposed the person to cancer. So the patient might have gotten cancer even without a transplant.
The NCI study found that lung cancers were most often found in the remaining original lung. Research has shown that cancers found in the first six months after a transplant could be "delayed reports of cancer found in the [removed] lung," according to the study.
Dr. Jonathan Bromberg, head of the Division of Transplantation at the University of Maryland Medical Center, applauded the new research. But he said it would have been even better if it had compared transplant patients to those who have the disease but did not receive transplants.
"If you have chronic kidney disease, if you are on dialysis, you have a higher chance of getting cancer," Bromberg said.