TORONTO — Quebec can expect to see higher rates of breast cancer among women who carry gene mutations known to increase the risk of that form of cancer, because women in that province who are screened for the genes are less likely to take preventive actions, a new study reports.

Women from Quebec who test positive for either the BRCA1 or BRCA2 gene mutations are less likely than women from Ontario or Western Canada to have surgery to remove their breasts or their ovaries, according to the study. These surgeries are proven to substantially reduce a mutation carrier's very high risk of developing breast or ovarian cancers.

"It is concerning to us. And it's concerning to me when I'm looking at women, especially in Quebec," said lead author Kelly Metcalfe, a professor in the faculty of nursing at the University of Toronto.

"This is going to translate into more cancers in Quebec than in B.C."

The study, published Tuesday in the journal Open Medicine, followed up 672 women who had screened positive for one or the other of the gene mutations at genetic testing centres in Vancouver, Edmonton, Saskatoon, Winnipeg, Toronto, London, Hamilton and Montreal. The followup questionnaire was administered, on average, about four years after the genetic screening took place.

It's been about a decade since doctors have been able to screen women for these gene mutations, which are associated with staggeringly high rates of breast and ovarian cancers running through families. The authors wanted to see what women and their caregivers were doing with the information gleaned through the screening process.

"Really, the benefit of genetic testing is that we're able to let women know that they're at a very high risk of developing the disease and ultimately we hope that they do something about it so that they don't get cancer. Because really, that's the benefit of genetic testing," Metcalfe said.

Women with these mutations have an 87 per cent lifetime risk of developing breast cancer and a 40 per cent lifetime risk of developing ovarian cancer if they take no steps to reduce those risks.

Surgically removing both breasts lowers the breast cancer risk for these women by about 95 per cent. And mutation carriers under the age of 40 who have both ovaries removed lower their risk of breast cancer by about 50 per cent. As well, there may be benefits associated with taking the drugs tamoxifen or raloxifene or undergoing regular breast cancer screening using MRI rather than mammography.

Of the original group, 342 women were still breast cancer-free when the followup took place. Of that group, 21 per cent had undergone surgery to remove their breasts. (Some had the surgery before undergoing genetic testing, based on high rates of breast cancer in their families.)

Fifty-four per cent of the entire group had had surgery to remove their ovaries. But 46 per cent of the women who didn't have breast cancer - the group of 342 - had taken no preventive action.

Rates were not uniform across the country.

Two-thirds of the women from Quebec had taken no preventive steps. In contrast, a third of the women in Western Canada and Ontario had taken no action.

The biggest difference occurred in prophylactic (protective) mastectomies - 46 per cent of the women from Western Canada had the surgery compared to 22 per cent in Ontario and only eight per cent in Quebec.

When it came to surgery to remove ovaries, 67 per cent of the women from Western Canada had the procedure, followed by 61 per cent in Ontario and 39 per cent in Quebec.

Metcalfe said this study could not reveal why rates varied across the country - whether, for instance, women in different regions had different views about these emotionally difficult surgeries or whether the advice they were getting from their doctors varied.

"We don't know why it is. It could be that they don't have access. It could be that they're not being followed after they're given their results so they go home with their results and that's the end of it. It could be something cultural. We don't know what it is yet," Metcalfe said.

"That's what we have to do next. We have to determine why these discrepancies exist before we can ensure that all women are having equal access and they're getting the same type of information during counselling."