The study, published in The Lancet Oncology, found 12% of 2,733 women aged 18 to 40 treated for breast cancer at 127 hospitals across the UK between 2000 and 2008 had a BRCA mutation.
But the researchers said surgery may still be beneficial for these patients to reduce their risk of a new cancer developing in the longer term.
The study's author, Professor Diana Eccles, of the University of Southampton, said: "Women diagnosed with early breast cancer who carry a BRCA mutation are often offered double mastectomies soon after their diagnosis or chemotherapy treatment.
"However, our findings suggest that this surgery does not have to be immediately undertaken along with the other treatment." Fiona MacNeill, of the Royal Marsden NHS Foundation Trust, who was not involved in the research, said: "This study can reassure young women with breast cancer, particularly those with triple negative cancer or who are BRCA carriers, that breast conservation with radiotherapy is a safe option in the first decade after diagnosis and double mastectomy is not essential or mandatory at initial treatment.
"In particular, being able to give some women with triple negative breast cancer the choice to delay a risk-reducing mastectomy would allow them to take back control of a major part of their treatment and offer them more time to recover from their initial therapy." She said she was now keen to understand how women fared more than 10 years after their diagnosis.