Dec. 4, 2002. 05:44 AM

Faulty gene, birth control pill increase cancer risk
One in 200 carry mutation Risk greater for women under 30

TANYA TALAGA
MEDICAL REPORTER

Young women who carry a faulty gene that puts them at risk of breast cancer should avoid prolonged use of the birth control pill, a new study suggests.

Women who carry mutations in the BRCA1 gene may be at higher risk of early onset breast cancer if they've used the pill for five years or more, according to research from Dr. Steven Narod, chair of breast cancer research at Sunnybrook and Women's College Health Sciences Centre.

Women carrying BRCA1 or BRCA2 genetic mutations are at a 50 to 80 per cent risk of developing breast cancer.

About one in 200 Canadian women carry one of these mutations. However, if you are a Jewish woman, your chances of carrying a mutation are about one in 50.

Among carriers of BRCA1, women using the pill for five or more years have a 33 per cent increase in their risk of early onset breast cancer, compared to women who never used the pill, Narod found.

The research compared cancer history and contraceptive use for about 2,600 women from 11 countries who carry gene mutations.

That number was split between women who have the disease and those who don't.

Narod's research points to an elevated risk of disease for women using the pill before age 30, women who were diagnosed with breast cancer before age 40 and those who first used the pill before 1975.

"Under the age of 25, I'd probably think of another form of contraception," said Narod. His findings only apply to women carrying the mutations.

Ashley, a 20-year-old Toronto-area woman, is a BRCA1 carrier with a family history of the disease. She's a new mother who doesn't want her last name used because of her carrier status. She says knowing she carries the faulty gene makes her feel proactive about her health.

"Knowing I've got the gene, I can help prevent the disease," she said. She watches her diet, conducts regular breast self-exams and avoids the pill. "If I didn't know, I wouldn't think about those things."

There isn't a definite explanation as to why women under 30 are at greater risk once they take the pill, but it was what the research showed.

It is believed the risk factors of breast cancer can change with age.

In an interesting twist, if women who are carriers use the pill after 30, their risk seems to diminish, the study notes. Narod adds that women who are in this age group and who are gene carriers may want to take the pill in an attempt to reduce their risk of ovarian cancer.

Marjie Cohn Zacks, director of communications for the Ontario Chapter of the Canadian Breast Cancer Foundation, said it is important to note the study is only relevant to women who carry the mutation, not the general population. "Women who have the mutations need to discuss it with their doctors."

Cohn Zacks added that Narod's study is further evidence that there is a great need to seriously review all of the "practices that increase the exposure to hormones over a woman's lifetime."

Narod is one of Canada's leading genetic researchers. He is credited with helping to discover BRCA1 and BRCA2, two gene mutations that point to a greater hereditary risk of breast and ovarian cancer.

Use of the pill doesn't seem to be associated with an increased risk of breast cancer in BRCA2 carriers, but more study is needed to confirm these findings, Narod says.

The research is published in today's issue of the Journal of the National Cancer Institute.