Obesity and breast cancer

Obesity is associated with a poorer prognosis in women with hormone receptor positive breast cancer. From a study published July 2014 in the journal Maturitas.

It is widely accepted that women who are obese are at increased risk of various cancers, notably breast and uterine cancer. This may in part be because fat tissue produces oestrogen and higher production of oestrogens may ‘fuel’ some cancers. But more recently it has been shown that other factors produced by fat may play a role in cancer development, and possibly cancer progression.

Whereas many studies have shown higher rates of breast cancer in obese women, the impact of obesity on breast cancer survival is less clear.

The Woman’s Health Research Program at Monash University has looked at this in the Bupa Health and Wellbeing After Breast Cancer Study (the Bupa Study). This study involved 1,683 Victorian women with breast cancer, followed from diagnosis for 6 years. Of the 1,199 women with hormone receptor positive breast cancer,

  • 44% were of normal body weight (body mass index (BMI) 18.5 to less than 25kg/m2),
  • 31% were overweight (BMI 25 to less than 30kg/m2) and
  • 21% were obese (BMI 30 to less than 40kg/m2),

reflecting the increasing prevalence of obesity in Australian women.

Women that were overweight did not have an increased rate of recurrence and/or death from breast cancer than normal weight women at 6 years from diagnosis after taking into account age, stage of cancer at diagnosis and treatment given (chemotherapy, radiotherapy and endocrine therapy).

But, being obese at diagnosis was associated with a 70% greater risk of recurrence and/or death from breast cancer, after other factors were taken into account. For women with early breast cancer at diagnosis (stage I disease), being obese was associated with a threefold greater risk of recurrence and/or death from breast cancer.

These findings show that the link between obesity and breast cancer recurrence is not simply due to obese women having greater estrogen production by a greater fat mass. The findings support the hypothesis that obesity-associated insulin resistance and /or other factors produced in fat play an important role in the relationship between obesity and a poorer breast cancer prognosis.

What do our findings mean for women with breast cancer?

Many women choose to make lifestyle changes after being diagnosed with breast cancer. Obesity is something women can change, and women with breast cancer are receptive to life style changes that will enhance their survival. Our study findings indicate that weight reduction for obese women should be part of their overall breast cancer treatment plan, not just to enhance quality of life, but to improve their prognosis.

Robinson PJ, Bell RJ, Davis SR. Obesity is associated with a poorer prognosis in women with hormone receptor positive breast cancer. Maturitas. 2014 Nov;79(3):279-86. doi: 10.1016/j.maturitas.2014.07.004. Epub 2014 Jul 18.

Disclaimer: The above information is a general guide and was accurate at the time of production of this page. This information is designed to complement, not replace, the advice of your health professional.