Image caption The procedure involves grafting fat harvested from the patient by liposuction

Senior plastic surgeons have issued a warning over a breast enlargement procedure being offered by private UK clinics.

The British Association of Aesthetic Plastic Surgeons (BAAPS) say "stem-cell breast augmentations" are unproven and should not be offered commercially.

The warning came at the group's annual conference in Birmingham.

One Harley Street clinic offering the surgery responded by saying they were "confident" the treatment was safe.

Research 'hijacked'

The surgery involves using fat harvested from the patient's stomach or thighs via liposuction and using it to build up the breast.

Prior to transplantation, around half of of the fat is processed to enrich the stem-cell content - naturally occurring regenerative cells found within the fat.

The hope is that this enrichment process can improve the prospects for the fat graft.

The same technology is being used in reconstructive surgery where "cell-enriched fat grafting" is now being offered in several centres around the world to reconstruct breasts following cancer surgery.

Trials are currently under way at NHS centres in London, Glasgow, Swansea, Norwich and North Tyneside.

But BAAPS believes more clinical testing needs to be done to establish its safety before it is used commercially on healthy women.

We have to make sure whatever treatment we offer for breast augmentation is safe in the long-term Eva Weiler-Mithoff, Consultant plastic surgeon

"To think that this unproven research is hijacked and used in the commercial sector is really an appalling thought," former BAAPS president and consultant plastic surgeon Adam Searle told the BBC. "Not least when it's being utilised by inadequately trained practitioners."

Private London clinics, The Harley Street Skin Clinic and The Private Clinic of Harley Street, have been advertising stem-cell breast augmentations for some time. The latter says they will have treated some 200 patients by the end of this year.

In a statement, Dr Valentina Petrone of the The Private Clinic, said the views of BAAPS were welcome, but insisted the surgery was safe and every precaution was taken.

"The Private Clinic, is confident in respect to the safety of this treatment. Furthermore ongoing studies reassures us even more. We have strict patient selection criteria and clinical protocols in place.

"We, of course, look forward to completion of studies and any other findings as they become available over time and will, if necessary, adapt our protocols accordingly."

Cancer concern

The BAAPS warning came the same week new clinical data on cell-enriched fat grafting was presented to an conference in Nottingham.

Eva Weiler-Mithoff, a consultant surgeon at Canniesburn Plastic Surgery Unit in Glasgow, presented details of a 12-month trial to a meeting of the Oncoplastic Reconstructive Breast Surgery group.

The trial involved around 70 patients in seven centres in four countries. The data is yet to undergo peer review and was sponsored by Cytori Therapeutics, the US makers of a machine which can enrich the fat.

Media playback is unsupported on your device Media caption Consultant plastic surgeon Eva Weiler-Mithoff discusses the findings of a 12-month clinical trial

Ms Weiler-Mithoff told the BBC the procedure appears to be effective in cancer patients in filling in defects in the breast and in improving the appearance and feel of the breast. Nor were there any serious side-effects or recurrence of breast cancer to date.

"Traditional fat-grafting (in breast reconstructive surgery) does not work terribly well because there is not enough circulation to support the survival of the fat graft," she said.

"We know if we augment the fat graft with the naturally occurring regenerative cells in fat tissues we can improve the circulation around the fat graft and the survival of the fat graft."

But she said longer-term results were needed - at least five to10 years of data - before the technique could be deemed safe for use in cosmetic surgery.

"We still don't have enough long-term outcome data to say it's safe in the sense that it doesn't encourage the cancer to come back or new breast cancer to develop," she said.

"Because breast cancer is such a common disease we have to make sure whatever treatment we offer for breast augmentation is safe in the long-term."

A previous Japanese study involving 40 Japanese women undergoing cosmetic stem-cell breast augmentation also deemed the procedure to be effective, but also called for additional study.