Overweight women 'are more likely to relapse and die from breast cancer'
13:56 GMT, 23 March 2012
Risk factor: Carrying extra weight increases the chances of breast cancer returning, according to new research
Women who are overweight or obese when diagnosed with breast cancer are more likely to suffer relapse and die from the disease than lean women, say researchers.
A new study which found a link between increasing body size and worse outcomes has ruled out under-treatment with chemotherapy drugs as a possible cause.
It showed a 17 per cent increase in the risk of the disease coming back after initial treatment and the risk of death in obese women compared with those of healthy weight.
There was an eight per cent extra risk for overweight patients compared with leaner women.
US researchers believe higher insulin levels in fat women may be responsible for the difference in outlook compared to women of a healthy weight.
They say further investigation is needed to determine whether losing weight after treatment might improve the chances of survival.
The findings were presented at the 8th European Breast Cancer Conference (EBCC-8) in Vienna.
Dr Jennifer Ligibel, oncologist at Harvard Medical School, and colleagues, studied data from 1,909 patients who were enrolled into a study between 1997 and 1999.
The study was set up to investigate different doses of chemotherapy in patients where cancer cells were found in the lymph nodes, which means there is a higher chance of cancer returning after surgery.
Previously, it has been suggested that worse outcomes in overweight and obese women might be due to them receiving insufficient drugs because their body size had not been taken into account and they were getting doses designed for thinner women.
Using height and weight data from the patient records, the researchers analysed the relationship between body mass index (BMI) with relapse-free survival and overall survival after 11 years.
Overall, one-third of patients were of a healthy weight, one-third overweight and one-third obese, with one per cent underweight.
Dr Ligibel said lifestyle interventions could one day become a standard part of breast cancer care
Dr Ligibel found body mass index – the relationship between weight and height – was linked to recurrence and death rates.
Overall, a woman of healthy weight had a 77 per cent chance of surviving for 10 years, compared with a 70 per cent chance of survival for overweight and obese women diagnosed with breast cancer.
Around 29 per cent of women of healthy weight relapsed in the 10 years after diagnosis, compared with 34 per cent of overweight patients and 35 per cent of obese patients.
The study found a 1.5 per cent increase in risk for every one unit increase in BMI, resulting in an eight per cent higher risk for an overweight woman compared with a healthy weight woman.
The extra risk was at least 17 per cent for an obese patient.
Dr Ligibel said: 'Questions have been raised in the past whether obese women were receiving relatively lower doses of chemotherapy due to their weight.
'Our study mandated that each patient received a chemotherapy dose adjusted to her weight, so these results suggest that treatment factors are not responsible for the differences in recurrence rates seen in heavier women.'
In the UK around two-thirds of women are overweight or obese – a similar proportion to the US.
'You can see the way the problem is growing. That is why we think it is a matter of urgency to find out as much about the relationship between obesity and cancer as we can' said Dr Ligibel.
She said the increased risk might be due to higher insulin levels that occur naturally in fat women.
'Obesity is a modifiable factor, and although there is not yet enough evidence to say with certainty that losing weight or exercising more regularly will decrease the risk of breast cancer recurrence, there are consistent links between lifestyle factors such as diet, weight and physical activity patterns and breast cancer prognosis.
'If future studies show that making changes in lifestyle behaviours for women with early breast cancer will improve survival rates, then lifestyle interventions may one day become a standard part of breast cancer care' she added.
Professor David Cameron, from Edinburgh University and chair of EBCC-8 said: 'Whilst these are important findings for women with breast cancer, we need to recognise that the reason overweight women have poorer outcomes is not clear.
'There are a lot of health reasons why overweight women should try and get back to a normal weight, but this is not always easy, and as the authors acknowledge, we don't yet know that losing weight after a breast cancer diagnosis will make a difference.'
Dr Sarah Rawlings, Head of Policy at Breakthrough Breast Cancer, says: 'We already know there is a link between being overweight and risk of breast cancer. This study strongly suggests that being overweight at the time of diagnosis increases a woman’s risk of recurrence.
'We now need to prove whether losing weight after a breast cancer diagnosis can improve women’s outcome so we can help them at that point. Maintaining a healthy weight throughout life can help to reduce the risk of many diseases and improve general health.'