SALEM — It started as back pain and grew in intensity. An X-ray revealed a fractured vertebra. A blood test showed more: Alexander Meche, who was 5 at the time, had cancer — acute lymphoblastic leukemia.

"I think the most frightening thing to me was those (first) 24 hours," said his father, Mark Meche, a local architect. "We knew something was wrong but didn't know what it was."

Alexander was diagnosed on June 2, 2006. It's a date Mark and his wife, Kristin, won't forget.

More than a year and a half later, Alexander, now 7, is cancer-free. But it has been a long ordeal. He has been an inpatient at Massachusetts General Hospital in Boston and an outpatient at the hospital's pediatric cancer clinic. He has had cranial radiation and spinal taps and will be undergoing chemotherapy through next fall.

"He's mostly a trouper," his mother said. "He understands that taking your medication is not something we can negotiate — it's something we do."

When Alexander was diagnosed, the world stopped for the Meches, who have another son, Atticus, 11.

Mark Meche, a principal at Winter Street Architects, started delegating work to others. Active in several nonprofits and chairman of the board at Salem Academy Charter School, he also disengaged from many of his volunteer roles.

"I told them all, 'See you later,'" Meche said. "I turned my attention to what was really important."

Next month, Meche will run the Boston Marathon to raise money for the MGH clinic that has treated his son. He has run a marathon before and is training hard for this one, making almost daily runs from his home in Salem Willows.

He hopes to raise $26,385 for the marathon distance — 26 miles, 385 yards. It's a formidable goal, he knows, but he wants to try.

"If I come up with $15,000, that's OK, too," he said.

For the Meches, running the marathon on April 21 is a way to thank MGH.

"They saved our child's life," Kristin said. "We've always felt we were in capable and caring hands. They really care for us as a family and our child as a person."

To support the Meches' marathon goal, go to their Web site at www.PlatypusandSalamander.com.