The fear of harm, may have unnecessarily prevented some women from getting the full range of therapeutic care

Dr Lori Pierce, University of Michigan

It was thought that having these mutations, to the BRCA1 and BRCA2 genes, could make healthy cells less able to repair any damage caused by radiotherapy.

In addition, women carrying the genes, it was feared, might be more prone to side-effects such as pain, shortness of breath and fibrosis - the formation of scar-like tissue.

However, a study carried out by the University of Michigan Cancer Centre has concluded that women with the genes have no extra chance of either cancer recurrence, or these side-effects.

The team, led by oncologist Dr Lori Pierce, looked at 71 women with either of the gene mutations, and compared them to 213 women who had had similar diagnoses, surgical procedures and other treatments.

Five years later, the proportion of women in the "faulty gene" group whose cancer had returned was no higher than that in the group of genetically normal women.

Dr Pierce said: "With five years of follow up data in hand, we see no increased incidence of skin fibrosis, pain, shortness of breath or other side effects, which suggests that the DNA repair mechanisms are intact in BRCA1 and 2 mutation carriers.

'Fear of harm'

"The fear of harm, based on laboratory findings that the BRCA gene is linked to the cell's own repair system, may have unnecessarily prevented some women from getting the full range of therapeutic care."

Only approximately 5% of breast cancers are thought to be due to BRCA 1 or 2.

Dr Ross Sibson, director of cancer studies at the Clatterbridge Centre for Oncology in Merseyside, said that UK practice was to give radiotherapy where appropriate to everyone, regardless of faulty genes - unless concrete proof emerged that this could be harmful.

He said: "You could argue that the gene could be either an advantage or a disadvantage.

"Either the cancer cell could be so sensitive that it was unable to cope with a large amount of damage from radiotherapy - or that healthy cells are more likely to then grow abnormally if given a large amount or radiation.

"I think that in the absence of evidence to the contrary, while doctors would probably be more circumspect about giving radiotherapy to women with the gene, I doubt they would do anything different."