Six years ago, Suzanne Singletary traveled to central Florida to spend Christmas with her family.

She had a small cough, so she stopped at a local pharmacy to get some medication. 

“When I pulled into the parking lot, I coughed up a thin piece of blood the size of a strand of hair,” says Suzanne, 70, of Shell Point Beach, Florida. “It shook me up, though I didn’t tell my family. I didn’t want to spoil their Christmas...