Bone marrow transplants for curing cancer can themselves cause cancer many years later, a study found.
The reason appears to be the high doses of radiation that are a crucial part of marrow transplants.
Bone marrow transplants are widely used to treat leukemia and other blood cancers. Typically, doctors give high doses of chemotherapy and radiation to kill diseased bone marrow, then replace it with marrow from a donor.
The treatment can often cure these cancers. However, doctors were unsure how often the treatment prompts the growth of other cancers that emerge years later.
In the latest study, Rochelle E. Curtis and colleagues from the National Cancer Institute followed up on almost 20,000 people who received transplants from 1964 to 1992. They published their results in today's New England Journal of Medicine.
During the follow-up, the patients developed 80 new cases of non-blood tumors, while 30 would have been expected in this group.
The risk rose as time went by and was eight-times higher than expected 10 years after the transplants. By 15 years after the treatment, 7 percent had developed new cancers.
Despite the hazard, the researchers said marrow transplantation is a worthwhile treatment.