At present, the size of the tumour is the main consideration when a surgeon is deciding whether to try to remove just the lump, or the entire breast.
Current thinking is that a tumour 2cm or less across is suitable for a "lumpectomy", in which only the tumour and a small amount of surrounding tissue is taken out.
Anything bigger than this, and the surgeon will recommend a mastectomy - total breast removal, a traumatising experience for the woman involved.
But a team of researchers led by Dr Harry Bartelink of the Netherlands Cancer Institute in Amsterdam, carried out breast-conserving operations on hundreds of women with tumours up to 5cm across, and analysed the results.
The team found there was no significant difference in the survival rate of the women with larger tumours when compared with women whose smaller tumours had been removed.
The majority of women in developed countries have their cancer diagnosed before the lump reaches this size, so the implications are enormous.
More likely to return
Dr Bartelink said: "Breast conserving therapy instead of mastectomy can therefore now be offered to the large majority of breast cancer population."
The only difference between women with large and small tumours given the same operation was that the cancer was more likely to recur after treatment.
But this had no appreciable impact on overall 10-year survival rates.
The study, published in the Journal of the National Cancer Institute, caused excitement among UK experts.
Delyth Morgan, the chief executive of Breakthrough Breast Cancer, said: "Any procedure that reduces the need for radical surgery for women with breast cancer is to be welcomed.
"But we need to see further clinical trials before we can properly evaluate the long-term effects of lumpectomies for larger tumours.
"However, it does appear to offer hope for those women with larger tumours who at present require a mastectomy."