The novelist was diagnosed with stage-four cancer in 2009 but said it was actually two years earlier that she had found the lump.
"I thought, 'I'm not dealing with this' because in my mind I decided it was benign," she told the magazine. "I've had to deal with losing my mother (to breast cancer), my husband (to prostate cancer) and my fiancé (to lung cancer) and I did not want to put pressure on everybody in the family. So I happily, happily went day by day."
Collins was afraid of seeing the doctor given her family's history.
"I know we're all told to [get checkups], but some of us are too stupid, and I was one of them," she said in the interview. "That was my choice and maybe it was a foolish one, but it was my choice. Now I want to tell people it shouldn't be their choice."