Lindsey Stewart, left, doing homework in 2010. She was diagnosed with brain cancer more than three years earlier but continued to get straight A's. Mary Schnack, right, was diagnosed with endometrial stromal sarcoma in 1996. It recurred repeatedly until she'd had eight cancer surgeries. (Stewart Family Photo)

When my 14-year-old niece Lindsey died last year, my friend Mary took it personally. Although separated by decades, Mary Schnack and Lindsey Stewart shared a common menace: cancer.

Lindsey was diagnosed at age 10 with medulloblastoma, brain cancer. The most common malignant brain tumor in children, it is highly invasive and often fatal. Lindsey died two months short of her 15th birthday.

Mary had been diagnosed at age 40 with endometrial stromal sarcoma. ESS is rare, difficult to treat and often recurs. The typical survival time is three years.

When Mary heard about Lindsey, she reached out. She sent gifts for birthdays, gifts for Christmas, sometimes notes from her travels. When Lindsey's church in Grinnell, Iowa, printed T-shirts emblazoned with "Fight like Lindsey" and "Lindsey's Team," Mary wanted one.

Lindsey had surgery, radiation and chemotherapy, then went into remission. She decided she'd go to medical school.

"She could have done it, too," my brother said. "She was so smart."

Doctors warned that the treatments could impair her intelligence, but Lindsey continued to get straight A's.

A year later, in sixth grade, Lindsey wrote an essay in which she described the day of her diagnosis. She hadn't wanted to go to the hospital, even though her headaches were so severe she often vomited and cried. She knew something was very wrong and she was afraid to find out what. But that Saturday in 2006, she'd started losing her balance, so her parents took her to the ER.

The doctor wanted to do a CAT scan.

"I'm not a betting kind of man," he said, "but I bet you a nickel that the CAT scan will be fine."

After the test, they wheeled Lindsey back to the room and took her parents into the hall. They were gone for what seemed like forever.

Finally, her dad came in alone.

"Where is Mom?" Lindsey asked.

He didn't answer. He just sat at her bedside, clasped his hands and began to cry.

"I knew something was wrong," Lindsey wrote, "because Dad never cries."

Slowly, he started to speak: "They said there is a tumor in the back of your head."

"What does that mean? Am I going to be OK?"

"I kept crying and saying over and over again, 'I can't do this!,'" she wrote in her essay. "At the time, I never thought I could. I calmed down and my mom and I rode in an ambulance all the way to Iowa City…. The whole way down, I kept telling my mom it was going to be OK. Little did I know how much it would affect my whole life."

A year earlier, during treatments, her mother had said, "Lindsey, you know if I had a magic wand I could wave to take this all away, I would do it. You know that, don't you?"