"If the risk [of developing breast cancer] is high enough, doubling the risk of blood clots, many times, is worth trying to take the medication," Blackwell said. "It should be a discussion between every woman and her physician, and every woman should know her own individual risk factors for breast cancer."
When Robins, a BBC reporter, was on tamoxifen, she said first her periods became long but not heavy. Then she had two episodes of extreme dizziness and abdominal pain that prompted her to see her gynecologist for a dilation and curettage procedure. That same night, Robins became ill and lost her reproductive organs in the emergency hysterectomy, which sent her into early menopause.
To help Robins deal with the hot flashes, her doctors prescribed hormone replacement therapy, which was later linked to breast cancer in 2002, when researchers halted a trial of 160,000 women because so many of them developed aggressive breast cancer.
"Why run another risk of breast cancer when the whole reason I needed tamoxifen was to prevent breast cancer?" she said, adding that she often believes her existing cysts should have excluded her from the trial. "It was quite hard to have to endure, especially if you think it wasn't necessary actually."
Robins said her surgeon at the Royal Marsden in London knew she was part of the tamoxifen trial, but she can't remember whether he made the connection that the drug caused her cyst to rupture.
"However, something or somebody compelled me to ask whether I had been taking tamoxifen as opposed to the placebo," she said. Some trial participants took a placebo and others took tamoxifen, but they weren't told which was which. Upon hearing Robins' story, researchers told her she was taking tamoxifen.
Robins said she has not developed breast cancer. "I would just say [tamoxifen] is not a universal panacea," she said.