The sad news announced last week 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. Roberts’s 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 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, occurring in 1 to 2 percent of cancer patients, typically those who have had breast cancer or lymphoma.

Paul Tsongas, former US senator from Massachusetts and one-time presidential hopeful, died of MDS in 1997, more than a decade after his diagnosis with non-Hodgkin’s lymphoma.

MDS is 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, but success rates are a little higher in children and younger adults in good physical condition such as Roberts.