London: Obese women treated for breast cancer are 30 percent more likely to suffer a relapse than slimmer ones, a new study has claimed.
Researchers from New York found that extra body fat may cause hormonal changes and inflammation that may drive some cases to spread and recur, despite treatment, the Daily Mail reported.
The study found that there was a stepwise relationship between increasing body mass index and poor outcomes only in women with hormone receptor-positive breast cancer, the most common type of breast cancer.
Previously, it has been suggested that a greater risk of the disease returning in heavier women might be due to under-treatment with chemotherapy drugs.
It was feared they may have been receiving doses aimed at slimmer sufferers because their body size had not been taken into account.
The latest study of almost 7,000 female patients was led by Dr Joseph Sparano, of the Albert Einstein College of Medicine`s Montefiore Medical Center, in New York.
"We found that obesity at diagnosis is associated with about a 30 per cent higher risk of recurrence and a nearly 50 per cent higher risk of death, despite optimal treatment," he said.
"Treatment aimed at interfering with hormonal changes and inflammation caused by obesity may help reduce the risk of recurrence," he was quoted as saying by the paper.
The study compared the health outcomes of obese and overweight patients with others who took part in three trials sponsored by the National Cancer Institute.
Participants had to have normal heart, kidney, liver, and bone marrow function, excluding patients with other significant health problems.
Researchers were able to disentangle the influence of obesity from other factors.
The study found that increasing BMI, the relationship between weight and height significantly increased women`s risk of cancer recurrence and early death.
This was despite optimal treatment including chemotherapy and hormonal therapy.
Sparano said it was `biologically plausible` that increasing weight leads to greater risk of recurrence via higher insulin levels.
It was uncertain if losing weight after diagnosis could cut the risk of recurrence, but some studies suggest it reduces insulin levels, which "might be effective", he added.
The study was published in CANCER, a journal of the American Cancer Society.