LEWISTON – Patrick Dempsey hopes to draw thousands of people onto bicycles with an annual 100-mile trek though Androscoggin and Cumberland counties, beginning and ending here in Lewiston.

The trek and a 5 kilometer walk/run – “The Dempsey Challenge: A Journey for Hope” – are planned for Oct. 3 and 4, 2009.

On Monday, the movie actor and star of TV’s “Grey’s Anatomy” announced the event at Central Maine Medical Center and promised to cycle the trek’s entire route.

“I’ve never done 100 miles in a single day,” said Dempsey, who grew up in Turner and Buckfield. But he’s already begun training near his southern California home, where he rides a regular 25-mile route.

The October event is aimed at getting people moving and raising money for the cancer center that bears his name.

“I wanted to do something that is true to me,” said Dempsey, who has been an active cyclist for about three years. “It’s promoting health and taking care of your body.”

Dempsey plans to use his celebrity to invite the world’s most famous cyclist – Lance Armstrong – to join the ride.

“We will extend an invitation to him and hopefully he’ll come,” he said. “He’s done a lot for cycling and cancer, so it would be a wonderful thing to have him there.”

Dempsey also hopes to bring along several professional racers.

Proceeds from the trek, the walk/run and other events will go to the Patrick Dempsey Center for Cancer Hope and Healing, which began operations in April.

Dempsey established the center as a way of reaching out to cancer patients and their families and meeting needs not met in the traditional hospital setting.

Since it started at Central Maine Medical Center with an initial $250,000 donation from Dempsey, the center has had 2,100 contacts with patients and their care-givers. The center’s help line has also responded to more than 1,400 calls.

“We’ve been at this for only eight months,” said Peter Chalke, Central Maine Health Care’s president. Yet the center offers support groups, counseling, yoga, massage and even transportation.

The center has also drawn some big contributors.

The Avon Corp. has awarded the center with a $500,000 grant; the Tallen-Kane Foundation awarded it $25,000.

And a cocktail party fundraiser to be held late Monday with Dempsey was expected to raise another $36,000.

The bike tour is being managed in part by Medalist Sports of Atlanta, an international company that runs several high-profile sports events, including some of Armstrong’s LiveStrong Foundation bicycle treks.

According to the center’s Web site, www.dempseycenter.org, the October event will also include a “Champions of Hope” banquet and, for special donors, a chance to ride with the actor during the trek.

Dempsey said he was drawn to create the center as he watched cancer strike his own family. His mother has twice beaten ovarian cancer and is in remission following a third diagnosis.

“There’s no cancer-free,” said Mary Dempsey, the actor’s sister and a coordinator with the cancer center. “There is just living a healthy, vibrant life.”

The 5k walk/run was added to the event in part for their mom, who walks every day.

“It’s a part of her life,” said Patrick Dempsey, who insisted that the exercise is almost as much about a sense of well-being as it is about physical fitness.

He’d ride more than he does if time permitted, he said.

“I get rid of a lot of the anxieties and frustrations that come up,” he said.

Of course, unlike the rest of us, he is sometimes trailed by photographers when he goes for a ride. He doesn’t let them bother him, he said.

“If I worried about them, I’d never leave my house,” he said.