Breast cancer treatment found to boost leukemia risk

Older breast cancer patients who get drugs to boost their immune systems during chemotherapy double their risk of developing leukemia later on, a new study has found.

The study, which appears in today’s issue of the Journal of the National Cancer Institute, reported that women over 65 who took growth factors had a 2% chance of being diagnosed with acute myeloid leukemia or pre-leukemia (myelodysplastic syndrome). By comparison, patients who did not take growth factors had about a 1% chance.

The researchers noted that the absolute risk remained small, and said the benefits of growth factors probably still outweighed their risks. But it is one more thing for cancer patients to take into account when deciding on a course of treatment.

“It does add a new dimension to our decision-making in this particular age group,” said Dr. Kathy Albain of Loyola University Medical Center, who was not involved in the study.

Meanwhile, the Food and Drug Administration on Tuesday approved a molecular test that predicts breast cancer recurrence by profiling the activity of 70 genes. The test, MammaPrint, has been used in Europe since 2005.

But U.S. cancer experts were less than enthusiastic.

Dr. Daniel B. Hayes, clinical director of the breast oncology program at the University of Michigan, said the test was “not very practical” because it required fresh-frozen tissue.

But more important, said Hayes and Albain, the developers of the test do not have the clinical data to tell doctors how the test should be used.

For women with early-stage breast cancer, chemotherapy has become an increasingly popular option. Numerous studies have shown it improves the odds of survival; and newer drugs have made it more tolerable, allowing many women to continue their regular activities throughout their treatment.

But experts say only a minority of patients who get chemotherapy actually benefit from it: Most are fine without it, and some will die despite it. A central goal of cancer research is to be able to predict who will benefit from toxic treatments so the rest can be spared.

One of the side effects of chemotherapy is a dangerous reduction in white blood cell counts that leaves the patient vulnerable to infections. Growth factors such as G-CSF (granulocyte colony-stimulating factor), known by the trade name Neupogen, and GM-CSF (granulocyte-macrophage colony-stimulating factor) boost the patient’s production of white blood cells.

In the new study, researchers looked at more than 5,500 breast cancer patients who were diagnosed between 1991 and 1999, and followed them until 2003. In all, 64 women were diagnosed with leukemia or pre-leukemia. But for the women who received growth factors (mainly Neupogen), the risk of getting leukemia was twice as great as for the others.

The researchers caution that they can’t prove the growth factors are the cause of the patients’ blood cancer. It’s possible that whatever led to growth factors being needed (such as dangerously low blood counts) also caused the leukemia.

Dr. Charles Bennett of Northwestern University, who was part of the research team, said there was mounting evidence that those who developed leukemia or pre-leukemia after taking growth factors might have had some predisposition.

“If the patient has an underlying genetic risk for leukemia, then this growth factor may bring it out,” Bennett said.