Oscar-winning actress Angelina Jolie's decision to have her ovaries and fallopian tubes removed will reduce her risk for ovarian cancer, but won't eliminate it entirely, says a Canadian oncologist.

Jolie announced Tuesday that she had undergone the preventative surgery after learning from her doctors that blood tests had revealed possible early signs of ovarian cancer.

The news worried Jolie since cancer of the ovaries killed her mother and her grandmother. As well, genetic tests two years ago revealed that Jolie carried a mutation of her BRCA1 gene that gave her an estimated 87 per cent risk of breast cancer and a 50 per cent risk of ovarian cancer.

Dr. Maureen Turner, head of medical oncology at Sunnybrook's Odette Cancer Centre in Toronto, says by having the surgery now, Jolie has cut her ovarian cancer risk from 50 per cent to about five per cent.

"And that's because the lining of the abdomen, called the peritoneum, is made up of the same cells as those that cover the ovaries and the fallopian tubes," Turner explained.

"So you can't remove all risk, but you can remove as much as possible."

'So much clarity'

Jolie underwent a preventive double mastectomy in early 2013. In a column in The New York Times Tuesday, the actress said she had always planned to have surgery to also remove her fallopian tubes and ovaries – called a salpingo-oophorectomy – but thought she could wait.

The blood test results two weeks ago left her worried that cancer might have already begun to grow.

"I went through what I imagine thousands of other women have felt. I told myself to stay calm, to be strong, and that I had no reason to think I wouldn’t live to see my children grow up and to meet my grandchildren," she wrote.

"…The beautiful thing about such moments in life is that there is so much clarity. You know what you live for and what matters."

To Jolie's relief, tests showed there were no tumours on her ovaries. But she decided it was time to go ahead with the surgery.

She is now taking hormone replacements to help her ease her transition into menopause.

"I feel feminine, and grounded in the choices I am making for myself and my family. I know my children will never have to say, 'Mom died of ovarian cancer,'" wrote Jolie, who has six children: Maddox, 13, Pax, 11 and Zahara 10, Shiloh, eight, and six-year-old twins Knox and Vivienne.

'Angelina Effect'

After Jolie published an op-ed about her double mastectomy in 2013, Canadian researchers noted a distinct "Angelina effect," with hundreds of women at risk of hereditary breast cancer going to their doctors to have their own genetic testing done.

At the Odette Centre alone, the number of women referred for genetic counselling increasing by 90 per cent in the six months after Jolie's story was published. What' more, the vast majority were women who were at highest risk for the genetic mutation and thus those who would benefit most from testing.

When celebrities come forward with revelations about their medical choices, they often create confusion among the public, but Turner says that has not been the case with Jolie's discussion of her cancer risk.

"In this case, it has been a very important public service that she has undertaken," she said.

Jolie wrote in her piece that, for young women considering the preventive surgery she had, there are procedures in which women can remove their fallopian tubes but still keep their ovaries.

"I hope they can be aware of that," Jolie wrote.

"It is not easy to make these decisions. But it is possible to take control and tackle head-on any health issue. You can seek advice, learn about the options and make choices that are right for you. Knowledge is power."