WOMEN with a gene linked to breast cancer greatly increase their chances of contracting the disease through long-term use of the pill and hormone replacement therapy, new research has revealed.
The Europe-wide study has given new weight to the argument that hundreds of Scottish women with the gene should consider having their ovaries removed.
Previously, studies have suggested that an increased cancer risk in women can be linked to the extra amounts of the female hormone oestrogen they receive through long-term use of the pill or HRT.
But it had been assumed that women with high-risk genes suffered from a type of breast cancer that was caused by their genetic make-up rather than their exposure to oestrogen.
However, the new study, which examined more than 3,000 women with breast cancer across Europe, found that women with the breast cancer gene were, in fact, 70 per cent more likely to have been long– term users of the pill or HRT than those without the gene.
"It was clear that those with the BRCA gene mutation had greater risk if there had been long-term use of the contraceptive pill," said Professor Michael Steel, of St Andrews University's Bute Medical School and one of the report's authors.
"That risk was even more if they had the gene mutation. For the first time, we produced evidence that they are more sensitive to the effect of contraceptives and HRT than other women."
Around three in every thousand women are estimated to have the BRCA mutation – a ratio that suggests more than 800 women in Scotland have the breast cancer gene.
A total of 3,123 women across Europe who had been diagnosed with breast cancer before the age of 45 were recruited for the study.
Their family histories were examined to find out if they were likely to be carriers of the breast cancer gene. On that basis they were divided into 382 "genetic" cases and 1,333 "sporadic" cases.
The use of the pill and HRT was analysed in both groups.
Professor Steel said: "In the general population (the increased risk of breast cancer linked to the pill and HRT] has been known for quite some time.
"What we didn't know was whether that also applied to the special sub-group of women who have got inherited risk.
"The question is whether they should be advised to avoid the things that raise the risk in the general population, and the answer seems to be 'yes', at least for the oral contraceptive pill and HRT."
Prof Steel said that the study reinforced suggestions that removing women's ovaries was a good way of preventing cancer.
Some women with a high risk of getting the disease have had their ovaries removed on the basis that they arethe glands that produce oestrogen.
Prof Steel said: "There is now very good evidence that if you can demonstrate a high genetic risk, removal of the ovaries at around 40, when women have decided not to have any more children, is definitely a good way of reducing the risk. We don't understand quite why."
In the past, Prof Steel said it had been assumed that there were limited benefits in blocking oestrogen for those with high-risk genes.
"It is now clear that there is benefit from removal of the ovaries and from avoiding long-term use of hormones."
Cancer charities reacted with caution to the latest research, warning that there were benefits from the pill and HRT.
Nell Barrie, Cancer Research UK's science information officer, said: "We already know the contraceptive pill can slightly increase a woman's risk of developing breast cancer, but this risk returns to normal within 10 years of stopping the pill.
"This study suggests the pill could increase breast cancer risk in women with faulty BRCA genes by more than it does in women without these gene faults. But the results are not conclusive. It's important to note the pill can offer protection against ovarian and womb cancer. Your doctor can help you decide what's best for you."
Additional reporting: Calum Liddle and Demian Hobby
MHAIRI Sommerville has never forgotten the moment she learned she had a hereditary high risk of developing cancer. Tests of her genetic susceptibility to the disease had been prompted by the diagnosis of bowel cancer in her father the previous year.
"I actually got told over the phone and I was in shock when I heard," said Somerville, now 36, from Wishaw. "I thought 'Oh my God, I'm going to get cancer'. Everything was going through my head and I knew I was high risk, but then after sitting down and thinking over it with family I realised it was OK.
"I could prevent it and I knew I'd never be in a dangerous position because medical staff could keep checking up on me."
The initial tests were prompted by Sommerville's father being diagnosed with bowel cancer.
Sommerville's recommended course of action was the removal of her ovaries and her womb in what is termed a full hysterectomy.
Going ahead meant she had no future prospect of having children. However, the decision was made easier by the fact that she already had three children – two sons, Andrew and Dale, and a daughter Aileagh.
After the hysterectomy Sommerville made a full recovery in three months and has since returned to specialists for yearly check-ups.