One in five women with breast cancer who undergo breast conserving surgery rather than a mastectomy will need a second operation, according to a major UK study.

The results, published in BMJ, confirm the findings of previous, smaller studies. It is standard for women who opt for breast conserving surgery to be informed about the risks involved in removing only part of the breast.

Around 45,000 women are diagnosed with breast cancer each year in the UK. Of these, 58 per cent chose to have only part of their breast removed rather than a mastectomy, which sees the whole breast removed.

When combined with radiotherapy, breast conserving surgery produces similar survival rates to those achieved with mastectomy alone.

But because some tumours prove hard to fully define with imaging techniques, breast conserving surgery may occasionally result in cancer cells being left behind and require a second operation.

The study examined the reoperation rates of 55,297 women who had primary breast conserving surgery in 156 NHS trusts in England between April 2005 and March 2008.

Of these women, 11,032 needed a second operation within three months. Around 40 per cent of women who had a reoperation underwent a mastectomy. And among the women who needed a second operation, and chose to have breast conserving surgery again, just one in seven needed a third operation.

Commenting on the research, Mr Ramsey Cutress, Cancer Research UK breast cancer surgeon at University of Southampton, said: "This is a very interesting and important study on a large group of UK women, and previous studies, in the UK and elsewhere, have shown similar results.

"It's standard practice to discuss the possibility of further surgery and it's important for patients to fully understand the pros and cons of this.

He said the aim of repeat operations after breast conserving surgery is to cut the chances that breast cancer will return - increasing survival.

"Rates of breast cancer recurrence are also reduced by other treatments such as radiotherapy, hormone therapy and chemotherapy where appropriate," he added.

"There's an ongoing need to better identify those at high risk of breast cancer recurrence, and to carefully select those who would benefit the most from further surgery."

Reoperation rates also varied between NHS trusts - in some Trusts reoperation rates were below 10 per cent while in others they were above 30 per cent - but the authors stress that further research is required to understand why this may be the case.

"Just over half of women diagnosed as having breast cancer in England now select breast conserving surgery as their primary treatment," the authors write.

"Cosmetic outcomes after surgery for breast cancer are an important consideration, and women should be made aware of the local rates of reoperation after primary breast conserving surgery, along with the likelihood of proceeding to mastectomy.

"In addition, breast cancer teams should do a local review of surgical technique, the definition of an adequate excision margin, imaging methods, and criteria for selecting patients.

"This may lead to an overall reduction in the reoperation rate after breast conserving surgery."

Source: CRUK