What is stage 0 breast cancer? Tina Knowles, recently diagnosed and treated, said she'd never heard of it—and she's not alone

Tina Knowles is certainly not alone in not knowing about stage 0 cancer—though it’s something that accounts for about 20% of all new breast cancer diagnoses, including those of Wanda Sykes, Elle Macpherson, Vanessa Bell Calloway, and, most recently, actress Danielle Fishel. Here's what you should know about this earliest form of breast cancer.