TORONTO, July 2 -- Last week, a colorectal surgeon at Toronto's University Health Network diagnosed cancer in three patients who, by every assumption that has shaped screening policy for a generation, were too young to have it. Two were in their thirties. One had not yet turned 30.

"Last week I saw two patients in their 30s diagnosed, and one patient in their late 20s," said Dr. Sami Chadi, the surgeon who treated them. As of July 1, the province where he practices stopped waiting for guideline committees to catch up with what he and his colleagues were already seeing in clinic. Ontario lowered its routine colorectal cancer screening age from 50 to 45, becoming the second Canadian province to do so after Prince Edward Island moved first ...