McKenna Wetzel, a playful girl who loved selling lemonade on the corner near her Huntington Beach home, was 7 when a tumor was discovered growing deep in her brain.

It's still growing in a laboratory at Stanford — the last living part of a girl who died two summers ago, and the part that killed her.

"You could take that petri dish," her mother, Kristine Wetzel, said, "I could slam it against the wall and I could kill those cells. But we couldn't kill them while they were in her."

Inoperable while McKenna was alive, the tumor is sustained in 2 million-cell batches in California, England, Australia and beyond by researchers who see it as one of the best hopes of finding a cure for the cancer.

Wetzel and her husband, Dave, created the McKenna Claire Foundation, which has raised nearly $500,000 to propagate donated tumor cells from their daughter and other children who have died. They hope the research they're funding will save the next set of kids stricken with the cancer that killed McKenna.

"There's so much you can't control with this disease and there's so much, especially at the end, that's devastating and out of your control. You watch your child lose the ability to speak, to move, to see, to hear, to swallow, to breathe," Kristine Wetzel said. "I wanted my daughter's death to have a purpose."

McKenna Claire Wetzel was told she had diffuse intrinsic pontine glioma, or DIPG, in January 2011. The rare cancer that weaves through a critical part of the brain is treatable in adults but considered a death sentence in children.

The family was buoyed by the promise of clinical trials, including one with Stanford researcher Dr. Michelle Monje, but none of the leads materialized.

The second-grader kept going to school at Eader Elementary. Classmates would stay inside with McKenna, who was struggling with her balance and needed help simply getting around, a family friend said. McKenna's friends came to her house every Tuesday night, and nearly 1,000 ­people attended a block party that raised about $50,000 meant to help pay for treatment, her mother said.

The Wetzels wanted McKenna to have as normal a life as possible, so they told her and her sister, Jordan, that they were trying to make McKenna feel better, not save her from a deadly disease.

'She knew'

"But she knew," Wetzel said. "She only cried one time that I know of. She was up in her room and I asked her, what's wrong? She said, 'You don't want to know, Mommy.' Then she wouldn't talk about it."

McKenna had begun to feel the effects of the tumor again, her mother said, after a couple of good months after radiation. ­Ultimately, their "last stand" against the cancer, as Wetzel put it, was to donate McKenna's brain tissue.

McKenna died in July 2011, just six months after her diagnosis. A lab tech flew down from Stanford to pick up the tumor. Today, tumors from McKenna and five other children who died of DIPG are tended by Anitha Pannuswami, a laboratory manager at Monje's lab at Stanford.

Monje's lab is one of a few in the world that harvest DIPG cancer cells so they can be bombed with drugs or implanted into mice for further study. The lines of cell ­replicas are key because little is known about DIPG.

McKenna, almost 8 when she died at home in her bed, was older than much of the in-depth research on the cancer. "We're very poor at treating it," Monje said. "Part of why that's true is that we haven't been able to study it well in the laboratory."

Monje's group established the first DIPG cell line in 2009 to better understand the biology and growth of the tumors, as well as how they react to drugs. "One of the tricks of this tumor, we're finding, is that no one thing is going to work. You have to have some kind of hypothesis-driven way to combine therapies," she said.

Available for research

Hired last year, Pannuswami grows the cells full time and ships them in ice to any researcher in the world who wants to study DIPG.

A small constellation of DIPG foundations named for sick or departed children lights the landscape of pediatric cancer funding. This one casts an uncommonly long shadow.

The McKenna Claire Foundation, formed soon after McKenna's death, has raised more than $400,000 in one year, trustees say, more than half of it through donations solicited from corporate-owned Chevron stations throughout Southern California in May 2012. This May, that program is expanding throughout California.

"That's the amazing part of how exponentially this has grown," said board member Darin Woinarowicz, a credit union executive who has set up other foundation boards.

Sponsoring the widespread replication of the cancer that killed McKenna brings anguish and a great deal of effort for Kristine Wetzel, a history teacher and Teacher of the Year at Tustin's Hillview High School, and Dave, who works for an auto-parts dealer.

"It is painful to the point where giving up is an everyday thought," Dave Wetzel said. "There's nothing we can do that will ever fill the void."