It is well known that breast cancer is the leading cause of death among female oncology patients. However, with the innovation of early diagnosis technology and tumor treatment technology, the survival rate of female breast cancer patients is increasing year by year. According to statistics, there were approximately 2.6 million breast cancer survivors in the UK and 560,000 in the US in 2008. Obesity is a highly prevalent health problem. According to statistics, there were approximately 500 million obese and 958 million overweight people worldwide in 2008. Obesity has been reported to be one of the major risk factors for the development of breast cancer in postmenopausal women. In addition, obesity is also strongly associated with tumor recurrence and poor prognosis in women with breast cancer. The results of numerous studies have shown that obesity is strongly associated with low survival rates in breast cancer patients. However, there is still no study on the extent of overweight in breast cancer patients and their mortality. To this end, a meta-analysis aimed at investigating the relationship between body mass index (BMI) and mortality in breast cancer patients was conducted by Professor Chan DS of Imperial College London and others and was recently published in Annals of Oncology. The study was a systematic review of 82 literature reports and a meta-analysis of 200,000 women involved in the study. Because the weight of breast cancer patients may change before and after diagnosis, the study was conducted in three different time periods: before diagnosis, up to 12 months after diagnosis, and 12 months after diagnosis, in order to more accurately analyze the relationship between BMI and total and breast cancer-specific mortality in breast cancer patients. The statistics show that there were 213,075 survivors and 41,477 deaths (including 23,182 breast cancer deaths) in the study. Compared to normal weight women with breast cancer, the combined relative risk of overall mortality was 1.41 for obese (pre-diagnosis BMI >30.0) women, 1.07 for overweight (pre-diagnosis BMI 25.0-<30.0) women, and 1.10 for underweight (pre-diagnosis BMI <18.5) women. For For obese women with breast cancer, the combined relative risk of overall mortality was 1.75 for premenopausal patients and 1.34 for postmenopausal patients. The risk of breast cancer-specific mortality increased by 17%, 18% and 29% before, up to 12 months after and after diagnosis, respectively. These results suggest that poor prognosis and poor survival in women with breast cancer are strongly associated with obesity, both before and after diagnosis. The higher the BMI of breast cancer patients, the higher the risk of death. However, further randomized clinical trials are needed to assess the effect of weight loss or no change in weight on patient mortality risk in women with breast cancer. In summary, obesity can be used as a poor prognostic indicator for women with breast cancer. Clinical oncologists can monitor patients' weight regularly during breast cancer diagnosis, treatment and follow-up in order to make an accurate assessment of patients' prognosis and survival. Lifestyle changes have been reported to potentially alleviate breast cancer patients and improve their survival rates, and breast cancer patients are advised to take care of improving their lifestyles after treatment.