Time is running out for 10-year-old Aden Knar.
"We're at last call," said his dad, Mike Knar.
The family has tried in vain to find a bone marrow donor for Aden, whose acute lymphoblastic leukemia went into remission for five years before returning in November.
Aden has been fighting blood cancer for two-thirds of his life, and his chances of survival are not good without a bone marrow transplant. The grueling but life-saving procedure essentially strips the body of its entire blood system and replaces it with that of another person's.
But doctors have told Aden's parents that he has a "weird DNA strand," his father said, which "doesn't happen that often for a child."
Aden's genes make finding a perfect match tough. None of his four older siblings fit. No suitable donors have surfaced on a worldwide registry of about 20 million people, and umbilical cord blood also has not yielded a match.
But the Knars know it's not impossible for someone with the right genes to turn up, and they still have hope.
That's why there's a third bone marrow donor drive this weekend, at Falcon Virtual Academy, where Aden has attended since kindergarten and is now a third-grader.
The drive will be held from 10 a.m. to 2 p.m. Saturday at the school, 6113 Constitution Ave., just east of Powers Boulevard.
The process takes about 15 minutes, said Dianna Hemphill, spokeswoman for Bonfils Blood Center of Denver, which is conducting the drive.
Would-be donors must be between 18 and 44 years old and in good health. After filling out a health questionnaire, candidates' mouths are swabbed for cells. The sample is then sent to the national registry and searched for a match.
About 12,000 people are waiting for a bone marrow transplant each year, 20 percent of whom are children, said Christian Snyder, director of the Colorado marrow donor program.
"We're usually able to fulfill about half of those," he said.
"It's kind of their last hope," Hemphill said. "They're already in dire circumstances when they get to this point."
People who match can donate their cells in two ways: either a fairly effortless procedure similar to a blood draw or a day-surgery method. The donor's body then regenerates the cells that are removed.
"It's a simple process, and you can save someone's life," Hemphill said.
Aden was diagnosed with cancer at age 4 and underwent extensive chemotherapy to gain remission. But one day in November, he told someone at the school that his legs were hurting.
That signaled the beginning of the relapse, said Jodi Fletcher, assistant principal.
"We were so excited; he was making such incredible progress," she said.
The first donor drive held at the school in January brought 250 participants, two of whom were matches for other people on the registry, but not Aden, Fletcher said.
The second drive held in February at several locations around town drew 118 people.
Aden, who Fletcher says is a "sweet boy" and best described as "quiet and quirky," has won the hearts of the school's 496 students.
Student Council members will hold a bake sale during Saturday's donor drive and other fundraisers to collect money to buy Aden a new recliner.
"It's just taking care of our own," Fletcher said. "Colorado Springs is a big city but a small community. We're trying to do everything we can. The outlook is grim."
Aden is again receiving chemotherapy at Children's Hospital Colorado in Aurora, which has eroded the quality of his life, said his dad, who co-owns SOCO Radio with his wife, Lori.
The treatment has taken a toll on Aden's small body. In February, he had heart failure. He has also weathered an E. coli infection, septic shock and pulmonary edema in recent months.
"It's a really horrible situation," Knar said. "It's brutal and shocking and hard to realize we can't do much. We're hoping for a good turnout on Saturday."