Obesity is associated with lower survival rates in women with ER positive HER2 negative breast cancer

The present study examined the association between obesity and survival rates by breast cancer subtypes. They found that survival rates were lower in obese patients, particularly in women whose tumors were hormone receptor positive and HER2 negative.

Obesity is defined as a Body Mass Index or BMI (weight divided by the square of height) of 30kg/m² and above. Obesity has been associated with worse prognosis (course of a disease) in breast cancer patients, but the relation between BMI and prognosis by tumor subtype has not been previously evaluated. Tumor subtype is defined by the presence of proteins called hormone receptors, which determine the tumors’ sensitivity to hormonal therapy. These include estrogen (ER), progesterone (PR) and HER2 receptors.     

Overall survival is defined as the percentage of patients in a study who are alive for a given period of time after diagnosis. Cancer-free survival refers to the percentage of patients who live free of the disease (without recurrence) for the same period of time. This study examined the relation between BMI and these survival rates. Rates were evaluated in subgroups, based on hormone receptors.

In this study, the authors looked at three different trials that evaluated postoperative chemotherapy. These trials included overall 6885 patients with operable breast cancer. About 37% were obese (BMI>30kg/m2), 32% were overweight (BMI=25-29.9kg/m2) and about 31% had normal weight (BMI=18.5-24.9kg/m2).

The study shows that, compared to non-obese, in obese and overweight women cancer-free survival and overall survival rate were reduced by 17% and 23% respectively. In patients with ER/PR-positive and HER2-negative cancer, obese patients had a 31% lower cancer-free survival and a 46% lower survival rate.
 

In summary, this study confirms the connection between obesity and inferior prognosis in breast cancer patients. Obese women with operable ER/PR positive, HER2-negative breast cancer were identified as a high-risk subgroup, as their prognosis is more affected by BMI.

However, future studies should test if weight loss after breast cancer diagnosis reduces the risks associated with obesity.