Sharon Stone Reflects on Breast Tumor Surgery: 'Don't Ever Feel Compelled Not to Get a Mammogram'

Sharon Stone is reflecting on the surgery she had to remove a large tumor in her breast, as she encouraged other women not to be afraid of testing for cancer.

While attending An Unforgettable Evening, a fundraiser for the Women's Cancer Research Fund on Thursday evening, the actress, 65, opened up to PEOPLE about how she was prepared to have her breasts removed after one of her mammograms flagged a potential problem.

Noting how she was "told that I had breast cancer, because I had a tumor that was larger than my breast — and they were sure that I couldn't possibly have that tumor without it being cancer," Stone said she later learned she did not have the illness.

"But I went into the hospital saying, 'If you open me up and it's cancer, please take my breasts, because I am not a person defined by my breasts,' " she continued.

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Stone revealed in her memoir The Beauty of Living Twice, which was released last year, that doctors had to remove benign tumors from her body in 2001 that were "gigantic, bigger than my breast alone."

Following the procedure, she shared that a plastic surgeon gave her larger breast implants without her consent when she was undergoing breast reconstruction surgery to repair her chest.

"When I was unbandaged, I discovered that I had a full cup-size bigger breasts, ones that he said 'go better with your hip size' " Stone said. "He had changed my body without my knowledge or consent."

And when Stone questioned her surgeon on her breast size, she said he told her that he "thought that I would look better with bigger, 'better' boobs."

The Basic Instinct actress, who was named an honoree at the event and received the Courage Award for her support of breast cancer research, told PEOPLE that she also had another surgery to remove tissue from her breast.

"And that might seem funny coming from me since you've all seen them. But let me tell you something else — you've seen them since the surgery, and you don't know it," she explained.

"So don't ever feel compelled not to get a mammogram, not to get a blood test, not to get surgery, because it doesn't matter," Stone added. "I'm standing here telling you I had one and a half and more tissue of my breast removed, and none of you even knew it."

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During her speech at the event on Thursday evening, Stone praised her hair stylist, who had done her hair for the night after undergoing her first round of chemotherapy to treat breast cancer. She asked every woman who "had or is dealing with breast cancer" in the room to "stand up" and be "brave" in supporting breast cancer research.

"We've been there. We've done that, and we've walked away without our breasts. Some of us have walked away without our friends, our moms, our sisters, our daughters, our wives. I can tell you, my kids' godparents died from [the] BRCA gene. I've lost a lot of friends to this. I don't want to lose anymore," she said.