Caitlin Rosenberg, left, donated bone marrow to sister Brooke when Brooke had blood cancer. They’ll wear Super Sisters capes in the Race for Every Child 5K. (Marvin Joseph/The Washington Post)

Sometimes, out of something bad, something good happens.

Brooke Rosenberg seems like any other 5-year-old girl. She’s happy, she smiles a lot and she jumps around as she talks, her bright blond hair shining in the sun. She likes the color pink, and she loves to tap dance. “If they have Olympic tap dancing, I want to be in that,” she said recently when asked what she wants to be when she grows up.

Brooke also really loves her big sister, Caitlin, who is 8. Caitlin looks out for her little sister, said the girls’ mom, Heather Rosenberg, and they play together. “We like to ride bikes. We like to play with Polly Pockets,” Caitlin said. But the two sisters, who live in Winchester and go to Greenwood Mill Elementary School, share a bond that runs even deeper than bikes and dolls.

Three years ago, Caitlin saved Brooke’s life.

Getting sick

Brooke was playing on the playground at school one day when her dad noticed she had a rash on her stomach and chest. Brooke was taken to the doctor later that day and had her blood tested to see if it was healthy. It wasn’t, and Brooke’s family learned that Brooke had a type of blood cancer called leukemia.

“Brooke had cancer,” Caitlin said, sitting on a shady wall in a park in Washington recently.

“And it hurt very bad, but I beat cancer,” Brooke said, sitting next to her big sister.

Brooke beat cancer because Caitlin was able to give Brooke some of her healthy bone marrow, which is a substance inside everyone’s bones where blood is made. Brooke first had to go through three months of chemotherapy, which is a treatment doctors use to kill the cancer. Then she was ready to get her sister’s healthy bone marrow.

Doctors gave Caitlin medicine that made her sleep and then took some of her bone marrow from the back of her hip bones. (Bone marrow grows back.) Caitlin said she felt like she was giving her sister energy to fight the cancer. When she woke up, Caitlin had bandages on her back. But she immediately asked to see her sister.

Feeling good today

The doctors won’t consider Brooke completely cancer-free for two more years, but today Brooke doesn’t remember much about being sick, the 41 / 2 months in the hospital or the day in November when she received Caitlin’s bone marrow.

“It feels really good once you’ve gone through with it,” Caitlin said about donating her bone marrow to her sister.

On Saturday, October 5, the girls will participate in the first Race for Every Child 5K and kids dash, an event that will benefit the Children’s National Medical Center in Washington, where the bone marrow transplant was done. The girls will be wearing pink capes with silver writing that says “Super Sisters” as they run and walk both the dash and the 5K.

It will be Caitlin’s second race. In 2011, she participated in Ashburn’s Journey 4 a Cure 5K, which raised money for kids cancer research.

“It’s really fun, and kids from the hospital need medicine to help them get better,” Caitlin said.

Caitlin and Brooke’s mom and dad will participate in the race, too.

“They have fun together,” their mom said. “They have a special bond that truly goes beyond what we could have hoped for.”

Have fun and help: The Race for Every Child 5K

What: Race for Every Child 5K run/walk and kids 100-yard dash. Event will include kid activities, including face painters, balloon artists, fun exercise activities and a magician.

Where: Freedom Plaza, 1455 Pennsylvania Avenue NW

When: Saturday, October 5. 7 a.m. to 8:15 a.m. packet pick up; 8:30 run/walk; 9:30 a.m. kids dash.

How much: $45 for age 11 and older. Kids ages 3 to 10 can run the dash for $10 and then walk or run with a family member who is participating in the 5K. Kids age 2 and younger in strollers are free. Register until October 3 by having a parent go to

Moira E. McLaughlin