LEWISTON — In just two years, a bicycle ride launched by the actor who plays Dr. McDreamy on “Grey’s Anatomy” has evolved into a festival of bicycling, running, walking, food and entertainment.

Nine big-name cyclists are expected to ride in the third annual Dempsey Challenge, the primary fundraiser for the Central Maine Medical Center’s Patrick Dempsey Center for Cancer Hope & Healing.

Dempsey, who was born in Lewiston and grew up in nearby Turner and Buckfield, was spurred to action by the experience of his 77-year-old mother’s battle with ovarian cancer in 1997. His mother, Amanda, has experienced several recurrences but she’s healthy and volunteers at the cancer center.

Today’s festivities focused on running and walking.

Sunday’s events will focus on cycling, with Dempsey leading riders on a 50-mile ride. Other rides were scheduled for 10, 25, 70 and 100 miles.

An avid cyclist, Dempsey will be joined by Connie Carpenter-Phinney and her husband, Davis Phinney, as well as Tour de France veterans Levi Leipheimer and six other pro cyclists. Both Phinneys and Carpenter-Phinney won medals in the 1984 Los Angeles Olympics.

It’s not a race. None of the events are timed, so the goal is to put the focus on the cause, not competition, said event manager Aimee Arsenault.

About 3,700 participants pre-registered, and another 300 were expected to sign up, Arsenault said.

She said the event was on track to meet or exceed last year’s fundraising of $1.2 million.