Breast cancer is more likely to kill obese women than those of normal weight, research suggests.
Breast cancer can spread
US researchers from the Fox Chase Cancer Center in Philadelphia examined data on more than 2,000 patients with early stage breast cancer.
They found obese patients were more likely to die from the disease, despite it being picked up early.
The research was presented at a meeting of the American Society for Therapeutic Radiology and Oncology.
The study also showed that breast cancer was more likely to spread to other parts of the body if the patient was obese.
Of the 2,010 patients, 452 were classed as of normal weight, 857 were overweight and 701 were obese.
The five-year survival rates for both normal weight and overweight patients was 92%, falling to 88% among those who were obese.
Lead researcher Penny Anderson said: "Our results show a statistically significant difference between obese women and the other groups.
"Because the prevalence of obesity increases with age, as does the risk of breast cancer, interventions that enhance weight control may have a substantial effect on breast cancer outcome."
Diet a factor
Antonia Bunnin, of the charity Breakthrough, said: "We already know that obesity after the menopause increases a woman's risk of developing breast cancer.
"This latest study adds to a growing body of evidence showing that obesity may also increase the risk of dying from the disease.
"Unlike many of the other established risk factors for the disease, obesity is, potentially, something we can change.
"Breakthrough Breast Cancer recommends that all women maintain a healthy weight by eating a healthy diet and regular exercise."
Previous research has shown that people who are obese are more likely to develop a range of cancers.
However, the impact of obesity on outcome is more unclear.
Earlier this year a British conference of cancer experts heard that food and drink caused as many as 80,000 cases of cancer each year in the UK.
A third of the cases could be blamed on obesity and over-consumption of alcohol, according to experts.
But the remaining two-thirds are linked to diet aspects which are as yet largely unknown, the Cancer Research UK conference was told.
Richard Sullivan from Cancer Research UK said: "This is an important study. It adds further weight to the evidence the we already have that obesity is a risk factor to take seriously for cancer."
But he said more research would be needed because the study was relatively small.