A spokesman for the Ride to Conquer Cancer, known as B.C.'s largest cyclist fundraiser, has confirmed the rider was killed shortly after 10 a.m. PT near Arlington, about 80 kilometres north of Seattle.
Snohomish County, south of Mount Vernon in Washington State.
"All who are associated with The Ride to Conquer Cancer have been deeply saddened by this news and our thoughts and prayers are with family and friends of the rider," said Doug Nelson, president and CEO of the BC Cancer Foundation.
The rider's identity and details on how he died has not yet been released.
Steve Sxwithultxw is riding in the event and said he heard a teenage boy was struck head-on by a car.
"What I've heard is that the young boy was riding with his uncle," he told CBC News.
"It was a particularly narrow road ... apparently someone's tire was clipped ... which sent the young boy into oncoming traffic."
Sxwithultxw said a member of his riding group, the First Nations Cancer Warriors, is a medical doctor who tried to help resuscitate the victim.
"He was pretty shaken up about it," Sxwithultxw said. "He says there's nothing that could have been done. He was pretty much already gone even though they worked on him. Emergency vehicles came upon the scene quite quickly, but unfortunately he was deceased."
On Saturday, more than 2,600 cyclists set off from Surrey's Cloverdale Fairgrounds on a 200-kilometre trek to Seattle.
- Read more about the Ride to Conquer Cancer
Since the event began in 2008, more than $50 million has been raised, making it the largest cycling fundraiser in the province's history.
This year, participants raised $10.4 million to support research at the BC cancer Agency.
More to come
Also on HuffPost