Robin Roberts has been diagnosed with MDS, a rare blood disorder, and will go on an extended medical leave Friday in preparation for a bone marrow transplant. Dr. Gail Roboz, who is helping Robin prepare her for her bone marrow transplant, appeared on " Good Morning America" today to discuss the medical road ahead. In the coming weeks, Dr. Roboz will help monitor Robin's health and progress.

Dr. Roboz answered some of questions the "GMA" staff and fans had about Robin's treatment, procedure and recovery process. Read her edited answers below.

What has Robin gone through to prepare for her bone marrow transplant?

Robin has received two cycles of a chemotherapy drug. You don't lose your hair, it doesn't make you sick. What it does is change the ways cells are dividing in the hope of improving the blood count and boostingthe level in the marrow. The concept here is to restore normal blood forming and marrow prior to transplant.

Why can't she just continue with that rebuilding form of chemotherapy instead of having the bone marrow transplant?

I hear this lot from patients who respond well to the medication and don't understand why they have to go through the rest of the treatment. But this chemo is not curative; it's reparative.

These types of medications can improve blood cells forming but it is temporary, measured in months or a year, rather than curative. [The vast majority of patients are unable to go through the rigors of stem cell replantation or don't have a donor available and need ongoing treatment for MDS].

A young patient like Robin wants to do more than improve. They want a cure.

What happens next?

Next for Robin is a chemo blast to prepare for the bone marrow transplant. Myeloablative chemo is different from what she has received so far. It lasts 10 days and will destroy her immune system, which is why she must be in isolation during that period.

Myelo means marrow and myeloablation [or myeloablative chemo] is designed to wipe out what is in the bone marrow before a bone marrow transplant. It will really wipe out her immune system so that it doesn't try to destroy the new cells that come in from her sister.

Even after the myeloablation, Robin's system still knows that the cells coming in aren't hers. Even though she has a perfect match, it would still attack those cells.

If we hit it just right, we will prevent any symptoms of graph vs. host disease [a rejection of the bone marrow transplant].

To find out more about bone marrow donation and sign up for a registration kit from the Be the Match Registry, click HERE.

How will she feel? What is happening?

She'll be tired, nauseous. But this is not the transplant procedure itself. This is not painful or hard to go through. After that's done, your body has a wiped out immune system. Sally Ann's cells will be trying to set up shop to set up an immune system and marrow to fight off infection. It takes time. You're completely vulnerable to infection and need to be on antibacterial, antifungals, and antibiotics. Your body is colonized with germs and even exposure from years ago can be dormant in your system.

The day a patient receives a bone marrow transplant is often called "Day Zero." What are the benchmarks in Robin's progress from there?

Days 0 - 30: The first 30 days are when the new cells are setting up shop and getting ready to regenerate. So many of my patients ask me, when the catheter is placed in her chest for the transplant, 'How do these cells know where to go? How do they find the bone marrow?' These cells have homing signals to help them find where they need to go and start growing and creating an environment for themselves.

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"Early recovery" is when the bone marrow is taking hold, and blood is being created normally.

[Until her donated cells engraft and] she starts making blood cells and platelets on her own, she's completely dependent on platelet and blood transfusions. It's about filling in for what your system can't do. It can't fight infections. The medications have to fight everything that's out there. You can't make cells or platelets, so you'll have transfusions. You can't eat, so we give you something to keep you nourished.

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This is a tough time in the treatment. There are mouth sores, weight loss, diarrhea, food doesn't taste good, there's hair loss.

What will her hospital set-up be like during this period?

The team is there the whole time, monitoring how you're feeling, what your experiencing, constantly. It's not the "intensive care unit" but its intensive care.

What will you be looking for and monitoring in the first 30 days?

We need to get through that period of wiped-out blood counts. We'll start to see white blood cells, red blood cells and platelets growing on their own. That's the evidence that the graph is working. That's when we breathe our initial sigh of relief. She'll need fewer transfusions, fewer medications, she'll be getting out of the hospital [after 30 days]. At that point, she'll still be on significant meds to regulate her immune system, but she'll be recovering at that point.

Talk about Days 30 to 100.

Starting at that 30 Day mark, she'll have bone marrow evaluations to see that it's growing normally.

In the days that follow - until the 100 day benchmark - we're seeing problems getting solved. She'll get off the meds, she won't feel as tired or as gross as you do when you're on so many pills. She'll start liking to eat again. She'll have to remind herself what she likes to do. You're separated from all that stuff for so long, you have to slowly reintroduce yourself to what you used to do.

Will she want visitors?

Probably not every day. It's a day to day thing. Well-wishers have to understand that the patient drives what's best for them. Sometimes it's best to let someone sleep.

When does she go home? If all goes well, Robin will go home after 30 days.

When she goes home she won't be feeling like herself, but we hope she'll be able to do some exercises, read and focus. It's important not to put a time stamp on anything. People are variable. Especially the way people are micromanaged in this process. You can't be worried if you're slower than others.

When will she feel like herself again?

Transplant is an individual experience. …We can't tell you how and when someone will feel better. Some people say they didn't feel 100% for a year. Others are ready to go back out much earlier.

What happens after the 100 Day Mark?

We have to watch patients super-closely for 100 days. We don't trust anything for the first 100 days. After that, we're happy. With cancer patients, we use five years as a benchmark to a cure. When someone has had a marrow transplant, we'll be watching her for life, to see if she's having symptoms.

How will you monitor when Robin will be able to come back to work?

We'll need to see high blood counts that don't require transfusions. She must be totally off antibiotics. Feeling sharp. There's an extra high bar for her because she has a harder job than most. She needs to have her system all up and running - marrow, immune system, nutrition - everything that was wiped out in chemotherapy has to be restored.

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