LEWISTON — Five hundred more bikers, walkers and runners signed on for the Dempsey Challenge in the past week, event organizer Aimee Arsenault said Friday.

That brought the total to 3,700 and counting. About 4,100 people rode, ran and walked in the event last year.

“We’re hoping for lots of on-site registrants,” Arsenault said.

The challenge, headlined by actor Patrick Dempsey, is the primary fundraising event for the Patrick Dempsey Center for Cancer Hope & Healing. Participants raised $1.2 million in 2010.

Arsenault shared eight things to know before this weekend’s challenge:

* Race headquarters is Simard-Payne Memorial Park.

It’s the site for the start of Saturday’s 10K run/walk (8 a.m.) and 5K run/walk (8:20 a.m.) and Sunday’s bike events (7:30 a.m., riders released in waves).

* Festival in the Park.

With bands, vendors, health screenings and the Prevent Cancer Super Colon, the free festival is running both days.

* Parking is free in Lewiston’s public garages for the weekend.

* It’s a green event.

That means no cups for water at rest stops; festival scraps are being composted; and Nike will have a Reuse-a-Shoe box to collect old sneakers to be ground up for reuse as athletic surfaces, such as playgrounds.

* Local roads will be closed for the 5K and 10K but not for the cycling.

Cyclists and drivers will have to be careful. Drivers also will have to find alternate routes around the Lewiston and Auburn downtowns, the Bernard Lown Peace Bridge and part of Route 136 between 8 and 9:30 Saturday morning.

The Lown bridge will also close between 7 and 8 a.m. Sunday, according to Lewiston police.

* Rest stops could be the best places for Dempsey photo ops.

Dempsey is riding the 50-mile course Sunday with professional cyclists (see below) and they plan to stop at four rest stops throughout the ride: Thos. Moser Cabinetmakers on Wright’s Landing in Auburn; Harvest Hill Farms’ Bakery on Bakerstown Road in Poland; Elm Street School in Mechanic Falls; then back to Thos. Moser.

* There will be more cycling pros than in past years.

Riding with Dempsey: professional racers Levi Leipheimer (biking the Dempsey Challenge for the second time), Tom Danielson, Coryn Rivera and Kristin McGrath, and retired professionals Davis Phinney and Connie Carpenter Phinney.

* The cancer survivor’s walk has moved to Saturday this year.

The free walk for cancer survivors, family members and caregivers starts at 10 a.m. It’s open to the public, no registration necessary and is only a “ceremonial mile” (less than an actual mile).

Dempsey and a bagpiper will lead the way.

“We’ve adjusted the route a little bit just so that folks can walk across the (challenge) finish line and feel what that feels like,” Arsenault said. “We have some folks who are undergoing chemo or have colostomy bags or are in wheelchairs. It’s really powerful for them to cross the finish line, symbolically and literally.”

For more information: dempseychallenge.org.

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