Observational studies demonstrate a strong association between obesity and both risk for breast cancer and prognosis in early stage breast cancer.
In a metaanalysis of more than 210,000 women with early stage breast cancer, the rate of breast cancer specific mortality was 35% higher in women with obesity at the time of diagnosis, than in women of normal weight.
A higher BMI at the time of diagnosis of breast cancer is predictive of a worse disease free and overall survival after correction for variables.
Weight change affects prognosis with greater weight change after diagnosis associated with higher rates recurrence, and all-cause mortality.
A metaanalysis found a 37% lower rate of breast cancer, specific mortality, and a 42% lower rate of all-cause mortality in breast cancer patients who had higher versus lower levels of physical activity after diagnosis, with an inverse dose response relationship.
There are beneficial effects of energy balance, interventions on outcomes, such as physical functioning, physical fitness, body composition, bone health, sleep, and quality of life in addition to reduction in fatigue, depression/anxiety, pain, and physiological, biomarkers of inflammation and insulin metabolism in breast cancer patients.
There is not a significant association between obesity and outcomes in metastatic breast cancer.
Body competition may be more strongly linked to outcomes, than weight or BMI alone.
Body weight comprises adipose and lean muscle tissue: Both have a significant effect on metabolism, inflammation, and immune regulation that could affect both the patient and tumor microenvironment.
Low muscle mass is repeatedly and significantly associated with worse survival and increased dose limiting toxicity in advanced cancers.
The evidence does not support a significant association between obesity and outcomes in metastatic breast cancer.