The breast cancer risk for British Asian women has increased, a study carried out in Leicester suggests.
Historically women from this ethnic group have had a lower risk of the disease than white British women, the University of Sheffield team said.
But they found breast cancer incidence had risen in recent years for South Asian women.
Experts said lifestyle factors such as obesity, or more coming forward for screening could explain the change.
The researchers, who are presenting their work to the National Cancer Intelligence Network Conference in Brighton on Friday, looked at census and cancer data for 135,000 women from different ethnic backgrounds from 2000-2009.
Between 2000-2004, South Asian women were found to have a 45% cent lower rate of breast cancer compared with white women.
But by the 2005-2009 period, rates of breast cancer among South Asian women had increased significantly and had risen to be 8% higher than white women, whose rates had not changed significantly.
Dr Matthew Day, of the University of Sheffield who led the study, said: "Historically South Asian women, and women in lower socio-economic groups, have been considered at lower risk of developing breast cancer.
"Based on our study in Leicester, this should no longer be considered the case."
He added: "The exact causes behind this change are not clear cut, they could relate to increases in screening uptake among these groups of women, which have in the past been shown to be lower than in other groups.
"Or they could be due to changes in lifestyle factors, like having fewer children and having them later in life, increased use of oral contraceptives, and increased smoking and alcohol intake - factors linked to increased breast cancer risk across the board."
Dr Mick Peake, clinical lead at Public Health England's National Cancer Intelligence Network, said: "The results of the Leicester study should assist public health services to both plan for, and respond to, the changing risk profile of breast cancer in the population, particularly with regards to Asian women who for a long time have been another group whose attendance rate for screening has been low.
"At the individual level, if women are concerned about breast cancer, they should speak to their GP."
Dr Hannah Bridges, of the charity Breakthrough Breast Cancer, says: "More research needs to be done to see if this trend is also true for South Asian women across the UK and to understand the reasons behind this potential change."