"It is the basic human biology of the breast maturation process through pregnancy that is the basis for the link between abortion and breast cancer," said Lanfranchi, president of the Breast Cancer Prevention Institute in the United States, clinical assistant professor of surgery at the Robert Wood Johnson Medical School and surgical co-director of the Sanofi-aventis Breast Care Centre at Steeplechase Cancer Centre in New Jersey.

Speaking at the University of St. Michael's College, Lanfranchi explained that during the first half of a woman's pregnancy, the volume of the breasts double in size up until about 20 weeks.

"So by 20 weeks, she's got 100-per-cent more breast tissue than she had to start with," she said. "But what type of tissue does she have? It's those immature cells and lobules where cancers form that she's made a lot more of."

But after a full-term pregnancy of 40 weeks or one that goes past 32 weeks, cancer risk is lowered as 85 per cent of the tissue has been changed into cancer-resistant type lobules, she said.

"After an induced abortion, you've left your breasts with more places for cancer to start," she said, since the pregnancy was terminated before the lobules could become cancer-resistant. "If a woman chooses to end her pregnancy with an induced abortion, she will necessarily have an increased risk of breast cancer because she denied herself the benefit of that full-term pregnancy."

Lanfranchi cited studies going as far back as 1957 supporting the abortion-breast cancer link, including studies from the United States, China, Turkey and Iran.

And in addition to a full-term pregnancy lowering a woman's risk of breast cancer, for each additional pregnancy, risk is lowered by another 10 per cent.     Women who have children at a younger age are even more protected, she said.

"A woman who has a full-term pregnancy at 18 has a 50- to 75-per-cent lower risk of getting breast cancer than if she waits to be 35," Lanfranchi said. "For every year a woman delays a full-term pregnancy after she reaches the age of 20, her risk of pre-menopausal breast cancer goes up five per cent per year and post-menopausal breast cancer by three per cent."

For more information on The Breast Cancer Prevention Institute, see www.bcpinstitute.org.