Nadia Popovici kept shifting her eyes from the hockey game to the back of Brian Hamilton’s neck.

Mr. Hamilton, an assistant equipment manager for the Vancouver Canucks, had a small mole there. It measured about two centimeters and was irregularly shaped and red-brown in color — possible characteristics of a cancerous mole, signs that Ms. Popovici had learned to spot while volunteering at hospitals as a nursing assistant. Read More