Women who are overweight or obese when they are diagnosed with breast cancer are at higher risk of cancer recurrence or related death than are leaner women, according to a new study to be presented to the 8th European Breast Cancer Conference (EBCC-8).

This finding held true even though the study mandated that chemotherapy dosage be adjusted for body weight, and adds further to the evidence that lifestyle factors can influence cancer prognosis, a researcher will tell the conference.

Dr. Jennifer Ligibel, a medical oncologist at the Dana-Farber Cancer Institute, Boston, USA, and an Associate Professor at Harvard Medical School, and colleagues, studied data from 1909 patients who were enrolled into a study called CALGB 9741 between 1997 and 1999.

The study was set up to investigate different dosing schedules for adjuvant chemotherapy in patients where cancer cells were found in the lymph nodes (node-positive cancer).

The presence of such cells in the lymph nodes means that there is a higher chance of cancer returning after surgery.

After extracting height and weight data from the patient records, they went on to evaluate the relationship between body mass index (BMI) with relapse-free survival (RFS) and overall survival (OS). 1.2% of the patients were underweight, 32.6% normal weight, 32.9% overweight, and 33.3% obese. 49% of patients were menopausal, 65% had oestrogen-receptor positive cancers, where the presence of oestrogen encourages the tumour to grow, and 70% received the oestrogen-receptor blocking treatment, tamoxifen.

“Several other studies have shown that being overweight or obese at the time that a woman is diagnosed with breast cancer is linked to a higher risk of recurrence. However, 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,” Dr. Ligibel will say. “We found that BMI was related to both RFS and OS; for example, the ten-year RFS of a patient who was overweight was 70%; compared with 65% for one who was obese.”

Although the link between obesity and the development of breast cancer is well known, there has been less research to date looking at its effect on cancer recurrence and survival.

“When you consider that data from 2007-8 show that 68% of US adults aged 20 years and over were overweight or obese, as compared to only 56% of the same group in 1998–1994, 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,” Dr. Ligibel will say.

The researchers intend to follow up their work by learning more about how weight-related factors could influence breast cancer outcomes. A number of studies currently underway are looking at how changing lifestyle behaviours, for example losing weight, exercising more, and eating a better diet, affects the hormones in women’s bodies that have been linked with breast cancer.

Ultimately, they say, they are interested in studying the impact of deliberate weight loss on the risk of recurrence in women with early breast cancer.

“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,” Dr. Ligibel will conclude.

Professor David Cameron, from the University of Edinburgh (Edinburgh, UK) 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.”

Source: ECCO