When Kate Gwynn was diagnosed with breast cancer in her early 30s, the oncologist did everything he could to save her breast. In the end he told Gwynn she could opt for a lumpectomy and follow-up radiotherapy, and that her long-term prognosis would be as good as if she had a mastectomy. But Gwynn, 33, weighed up the pros and cons and decided to go for breast removal anyway - which, a US consultant said this week, is what many women are choosing to do.

Dr Robert Kuske, of Arizona oncology services, says many women with breast cancer are put off less radical, breast-conserving surgery by the long and extensive course of radiotherapy that is usually also required. He says that as many as 80% of women with breast cancer are candidates for breast-conserving surgery - but that the inconvenience of six or seven weeks of radiotherapy, plus fears of irradiation of other body tissue, is extremely off-putting.

For Gwynn, radiotherapy was a lesser factor - the decision to have a mastectomy was largely an emotional one. "I felt my breast wasn't part of me any more," she says. "Once I knew there was cancer there, I didn't want it to be part of my body.

"My consultant started talking about other options, but I didn't want them. Once my breast was gone I could see the light at the end of the tunnel - that was the start of my recovery. You've only got one life, and I wanted to do everything I could to preserve mine."

The irony is that large-scale studies now show that long-term survival rates are just as good for many women with breast cancer whether they have a mastectomy or a lumpectomy plus radiotherapy. But, says Liz Cheesman, helpline manager at Breast Cancer Care, it is a mistake to think that survival rates are the only factor. "There are so many emotions involved. Some women feel very strongly that they just want their breast to be gone," she says. "I've spoken to people who have said they had to fight for a mastectomy when their consultant was in favour of less radical treatment.

"For other women, the reasons for choosing a mastectomy are practical. Radiotherapy can involve daily treatments at a hospital that might be a 50-mile round trip from your home, for six weeks or more; and one of the side-effects is tiredness. Other women worry about the wait they might have to get the radiotherapy - there is a shortage of radiotherapists and some people have to wait 16 to 20 weeks.

"With another group, the deciding factor is that with a mastectomy, it's clear-cut what will be involved. With a lumpectomy there's always the possibility of needing another operation, because they might not get all the tissue they need in the initial operation."

Breast cancer specialist Professor Trevor Powles, of the Parkside hospital in south London, says the picture in the UK is different from that in the US - here, he says, around 30% of women with breast cancer have a mastectomy, compared to around 60% in the US. The UK's multi-disciplinary approach to cancer care, he says, means it's easier for patients here to get a more comprehensive idea of treatment options at an earlier stage of their illness. "Whether or not a woman needs a mastectomy depends on the extent of the cancer and on its position in the breast. And more women can be prevented from having a mastectomy if they are given chemotherapy before surgery," he says.

He stresses, though, that he is talking about invasive breast cancer. Paradoxically, some women who are diagnosed with pre-invasive breast cancer, though it isn't such a serious disease, do require a mastectomy. "This cancer, which is also known as ductal carcinoma in situ, may be seen throughout the breast, which means a mastectomy is necessary," he says. The only consolation is that in these cases the long-term prognosis is excellent.

Oncologist Professor David Dodwell, of Leeds Teaching Hospitals Trust, says it is difficult to predict what a woman will decide to do when faced with different treatment options for breast cancer. He agrees that for some it comes down to a belief - whatever the studies say - that removing the breast tissue will make recurrence less likely, but he points out that this is a slippery-slope argument. "If a woman takes this attitude, what's to stop her thinking: should I keep the other breast? You can set off a train of unnecessary mutilation."

The other point he makes is that even a mastectomy cannot remove every trace of breast tissue - there is always the possibility of a recurrence of cancer in the chest wall, even after breast removal. "But for most women, breast cancer is a disease of one breast. When it's treated, the most likely outcome is that it's gone and it will never come back," he stresses.

Meanwhile, Kuske, in Arizona, is trialling a new form of radiotherapy called brachytherapy which would cut treatment time down to four to five days and confine its effects to 1-2cm of breast tissue. It involves placing a tiny radioactive seed inside the breast next to the cancer-containing tissue and, though it is still early days, the initial results look good.

· Breast Cancer Care helpline: 0808 8006000. Breakthrough breast cancer information line: 08080 100200.