Profits from the sale of each book will go to The Cure Starts Now Foundation, which they founded in honor of Elena. According to the Centers for Disease Control, cancer is the number one disease that kills children in the United States, more than cystic fibrosis, muscular dystrophy, asthma and AIDS combined.
Elena was diagnosed with Diffuse Intrinsic Pontine Glioma (DIPG) -- one of the most virulent forms of cancer that affects only about 200 to 300 children a year.
While Elena never knew she was dying, she was aware how devastating the disease was.
"It robs a child of one or two things a day -- rolling of the tongue, the ability to move a leg or write," her father said. "Each day, you wake and look at the body and wonder what you're losing."
Such was the case with Alexis Agin, who 18 months ago, was diagnosed with DIPG at the age of 2. She had been through months of seemingly unrelated symptoms: nightly vomiting, an apparent throat infection and acid reflux.
The Arlington, Va., girl then developed an "inverted eye" that her teachers and pediatrician thought might be innocuous, according to her father, Jonathan Agin, a 38-year-old lawyer.
But an MRI revealed cancer in her brain stem, like "sand strewn into grass and not a solid mass," he told ABCNews.com. The diagnosis came two weeks before his wife Neely found out she was pregnant with their son Gabriel, now 10 months old.
"We are still coping on a daily basis," he told ABCNews.com. "You get the news, then are essentially left without much assistance. That's when we started to research and find the best doctors."
Alexis received radiation, as did Elena -- a standard protocol for the disease -- and has since been asymptomatic, attending school and living a normal life.
The growth of the tumor has also slowed because she is part of a clinical trial of a new drug.
"She's one of lucky ones in this fight," said her father. "I try to do as much as possible with her and give her as normal life as possible, disciplining her as I would any other child. It's a difficult balance."
"Although Alexis is in progression of the disease, the fact that she has lived longer with it than most can give a margin of hope," he said.
The Agins met the Desseriches last summer and while lobbying for pediatric funding on Capitol Hill, agreed to head the Washington, D.C., chapter of their foundation.
"In my mind, while my daughter is still fighting and the treadmill is still moving, I can run on it and do all in my power to find treatments and researchers when a lot of physicians aren't because it's not worth their while."
Still, he is discouraged by the lack of funding, compared to adult cancers -- $24 million for pediatric research, compared to $520 million for breast cancer.
The brain tumors, like the ones in Elena and Alexis, are a "death sentence," with current therapies, according to Dr. Henry Friedman, co-deputy director of the Preston Robert Tisch Brain Tumor Center at Duke University.
"We have made no progress in three decades of work," he told ABCNews.com. "But with newer therapies that can produce newer outcomes, the hope of survival is always present."
These tumors cannot be removed by surgery without severing the brain stem. They resist radiation and chemotherapy treatments, said Friedman, who left pediatric for adult oncology because of frustration with poor funding.