Thousands of cyclists began riding from Toronto to Niagara Falls, Ont., on Saturday morning as part of the 12th annual Enbridge Ride to Conquer Cancer.

The cyclists are riding more than 200 kilometres in two days in support of Toronto's Princess Margaret Cancer Centre. A total of 4,573 are taking part.

Toronto Mayor John Tory helped to kick off the event on Saturday morning, thanking doctors, nurses, scientists, volunteers and patients in their fight against the deadly disease. The event has been dubbed Canada's largest cycling fundraiser for cancer medicine.

"How lucky are we, in so many respects in this city to have so much, but including one of the top five cancer research centres in all of the world," Tory said at Exhibition Place.

"I just hope you all have a safe ride and that you keep coming back, year after year, until we beat this demon that is affecting so many people and so many families in our great city."

Mayor John Tory, wearing his fancy Raptors jacket, told the crowd: 'I just hope you all have a safe ride and that you keep coming back, year after year, until we beat this demon that is affecting so many people and so many families in our great city.' (Paul Smith/CBC)

Opening ceremonies for the ride were held simultaneously in Toronto and Niagara Falls, the starting points for the ride. In Niagara Falls, riders take an opposite route into Toronto. The ride that begins in Toronto ends in Niagara Falls on Sunday afternoon.

The cyclists were told on Saturday, before the ride began under sunny skies, that they raised a total of $19.2 million for the Princess Margaret Cancer Centre.

For Joe Miszk and daughter Julianne Miszk, the ride is important. Julianne has bone cancer in her jaw, diagnosed more than two years ago, and has undergone three "chemo injury" surgeries plus radiation treatment. She has spent time in Toronto's Hospital for Sick Children.

"It's always been an important cause to me," Joe Miszk said. "She has tremendous fight in her. This is something that we wanted to do as a family together."

The father and daughter are riding together on a pink tandem bicycle. "It's been such a moving experience. And we want to find a cure for cancer. As a parent, especially, to watch your child go through this, it's the hardest thing. So we need to find a cure."

A total of 4,573 of cyclists is riding more than 200 kilometres in two days this weekend in support of Toronto's Princess Margaret Cancer Centre. (Paul Smith/CBC)

Julianne Miszk said she is riding for a friend, Jordan, who recently died. His photo was pinned to her back.

"This is my second year riding. I'm looking forward to it, all the food, and just riding and having fun, and seeing everyone cheer me on when I get to the finish line."

Along the route, hundreds of volunteers and crew members support the riders with meals, water, snack stops, transportation of gear, portable restrooms, safety, medical services and an overnight campsite with tents, hot showers and entertainment.

Similar rides are being held throughout the summer in Quebec, Alberta and B.C.

A riderless bike was escorted through the crowd during the opening ceremonies in honour of the late Dr. Hans Messner, a pioneer of allogenic bone marrow and stem cell transplantation in Canada.

A riderless bike was escorted through the crowd during the opening ceremony in honour of the late Dr. Hans Messner, a pioneer of allogenic bone marrow and stem cell transplantation in Canada. Here are members of his family and what is called the Heme Team, staff from the Princess Margaret. (Paul Smith/CBC)

All funds raised go to support what is called "personalized cancer medicine." That includes research, advances in treatment, education and new standards of care. Personalized cancer medicine is an approach to cancer care that focuses on the unique nature of each patient.

In the past 12 years, the ride in Ontario has raised more than $213.2 million. Nationally, the ride has raised more than $436.2 million.

Princess Margaret Cancer Centre says it has the expertise to treat more than 200 types of cancers.