Five years after treatment for breast cancer, "Good Morning America" ​​co-host Robin Roberts has a new health battle on his hands.

Roberts said Monday she started chemotherapy for the treatment of MDS, or MDS, blood and bone marrow disease, known as preleukemia. It is expected to receive a bone marrow transplant sometime this fall.

Her older sister, Sally Ann Roberts, an anchor for WWL-TV in New Orleans, is considered ideal to donate marrow, and said that she would do.

"My doctors tell me that I will beat this, and I know it's true," Roberts, 51, said on the show Monday.

Sally Ann Roberts said she was grateful to her brain is her sister can use and that it can help in its treatment.

"I'm so thankful that I did meet her, because there are a lot of people are dying for the match and no one in his family who are eligible," said Sally Ann Roberts.

She said that her family is now encouraging all to sign up to be donors.

"The wonderful thing about the donor that it takes so little," said Sally Ann Roberts. "I will go through physical and when ... Doctors believe this time I'll be prepared with some injection of the brain from the blood, and then just go through something like dialysis. I can miss weeks of work, if it's a lot."

Robin Roberts also hopes that the attention to her diagnosis will encourage people to donate bone marrow, which can help someone with this disease.

It has developed MDS as a result of treatment for breast cancer - a way to pass is so unusual, it only affects a few hundred people a year, said Dr. Richard Besser, medical correspondent for ABC.

The prognosis for many patients with MDS is very heavy, but it is mainly due to an illness affecting people over 60 years of age, Besser said. Between Roberts to be young and healthy, and is already in a good donor's sister, said Besser things look promising for her.

Roberts contributed to "Good Morning America" ​​since 1995, and was named co-anchor in 2005. Former Southeastern Louisiana basketball star has worked at ESPN for 15 years.

She had blood tests which revealed MDS feeling tired or more tired than even the one who had to get up to 7 o'clock in the morning show each weekday to be expected, Besser said.

She learned of her diagnosis on the same day that "Good Morning America" ​​beat "Today" for a week in the ranking for the first time in more than 16 years, Roberts said. On the day of some of her bone marrow was removed for testing, Roberts knew she landed an interview with President Barack Obama when the president showed his support for gay marriage.

"The combination of landing the biggest interview of my career, and with a drill in the back reminds me that God gives us what we can handle, and that it helps to have a good sense of humor when we run smack of misfortune in life," she said.

First lady Michelle Obama, via Twitter, told Roberts that "Barack and I have you in our prayers. We believe in you and thank you for your understanding and hope for others."

Roberts will take some random weekend on "Good Morning America," according to its response to treatment. She may need to take a few months away from the show soon after bone marrow transplantation. Currently, her team of colleagues, George Stephanopoulos, Josh Elliot, Lara Spencer, and Sam Champion chooses the slack for her, with a few co-hosts, as Elizabeth Vargas joining.

"GMA" runs on a surge rating in recent months, more and more to compete with the "Today" show than it was a few years.