The sad news announced today by Good Morning America host Robin Roberts that she’s battling a rare blood disorder similar to leukemia highlights the very real risks of cancer treatments. (Her heart-breaking interview posted above shows how tough it is to battle health problems while in the public eye.) Roberts’ condition, called myelodysplastic syndrome (MDS), is a pre-leukemia thought to be triggered by chemotherapy drugs given to her five years ago for breast cancer.

“It’s unfortunately something that happens typically five to seven years after treatment, but I’ve seen cases where it occurs 20 years later,” said Dr. David Steensma, an oncologist who treats MDS patients at the Dana Farber Cancer Institute. Both chemotherapy and radiation treatments can irreversibly damage the DNA of bone marrow cells, leading to a rise in new cancers.

Thankfully, the condition is uncommon, occuring in 1 to 2 percent of cancer patients, typically those who have had breast cancer or lymphoma.

Advertisement - Continue Reading Below

Former Massachusetts Senator Paul Tsongas—who ran unsuccessfully for president in 1992—died of MDS in 1997, developing it more than a decade after his diagnosis with non-Hodgkin’s lymphoma. The astronomer Carl Sagan also succumbed to it, as did writers Susan Sontag and Roald Dahl after their cancer treatments.

Unfortunately, MDS is really tough to treat—requiring chemotherapy and a stem cell transplant—with a low cure rate. Steensma tells me that only about 20 percent of patients are cured with the transplant: about 20 to 30 percent die of complications resulting from the transplant and the rest from MDS that’s resistant to treatment. Children and younger adults such as the 51-year-old Roberts have better cure rates, in the 30 to 40 percent range, Steensma added.

There’s no way to predict which cancer patients will develop MDS, and looking for common genetic patterns has been a goal of researchers for some time. Doctors aren’t able to determine how much genetic damage chemotherapy has wrought on individual patients, Steensma said, which also could help determine MDS risk and perhaps help in detecting it earlier.

Some progress has been made, however, in modifying treatments to lower the risk of this leukemia. When harsh chemotherapy treatments were first introduced for Hodgkin’s disease in the 1970s, doctors were thrilled that they finally had a cure for the cancer but dismayed that 4 to 5 percent of patients wound up developing MDS years later. Over the past 20 years, Steensma said, treatments shifted to a new regimen of gentler drugs that have the same cure rate but have lowered the rate of MDS to about 1 to 2 percent.

That still leaves the unsettling problem of using chemotherapy drugs to treat MDS, when those drugs may have caused the MDS in the first place. “It’s a Catch-22,” Steensma admitted, “and there’s certainly a risk of getting it again from the treatment, but it’s the only option patients have.”

Cancer patients also need to keep in mind that chemotherapy drugs are far more likely to cure them than present life-threatening side effects. But they should be told about this possibility when weighing the decision about whether or not to undergo certain treatments.