The Midnight in Paris star talked with Anderson Cooper on his show Anderson, and said that she had to keep the health scare private because she was advised to.
"I was contracted to go into a movie at that time, Little Black Book, with Brittany Murphy, who I miss very much," said the 63-year-old Oscar winner.
"My doctors at the time, they had to get insurance approval and all of that, so I was very quiet about it. I had to go back to work right away."
The actress, who stars on Harry's Law, went on to reveal that she underwent chemotherapy treatments by herself.
"I guess it's something I felt I had to face on my own," she elaborated. "Nobody else really knows what you're going through except another cancer patient. Even though your family is supportive and surrounds you."
However, Bates confessed: "If I go through it again, I think I would be a lot more open about it."
The Primary Colours star added: "I admire people who have been open like Melissa Etheridge and women I see walking around facing it without wigs and all of that stuff.
"I think I would be more courageous next time."