Obesity and high blood sugar at diagnosis have both been shown to worsen breast cancer prognosis. Hormone receptor positive breast cancer, which has both estrogen receptor positive (ER+) and progesterone receptor positive (PR+) tumor receptor status, appears to be especially vulnerable to the harmful effects these factors. However, merely being overweight at diagnosis does not appear to worsen prognosis.
Obesity appears to contribute to worse outcomes through factors associated with excess weight, including higher circulating insulin, glucose and estrogen levels, as well as inflammation, and growth factors secreted by fat cells. It is well established that type 2 diabetes, a condition characterized by abnormally high levels of blood sugar, is a risk factor for breast cancer. The effects of systemic treatment appear to be lost more rapidly in obese breast cancer patients. Since high blood sugar is frequently found in conjunction with obesity, it is difficult to separate their influence on breast cancer prognosis. Now a new study has reported that elevated fasting blood sugar and obesity each contribute independently to significantly worse prognosis in women with hormone receptor positive breast cancer.

Latest research finds both high BMI and high blood sugar influence prognosis

The study referenced at the beginning of this news article was designed to investigate the influence of fasting blood glucose and body mass index (BMI) at diagnosis on risk of breast cancer-specific death (death as a direct result of breast cancer and not due to another cause). The study included 1,607 women in five Italian cancer registries who were diagnosed between 2003 and 2005 and followed to year-end 2008. To conduct the study, the authors divided the women into the following three fasting glucose groups: ≤84.0, 84.1-94.0, > 94.0mg/dl and also took into account whether they had type 2 diabetes. The women were also divided into three groups according to BMI: ≤ 23.4, 23.5-27.3, > 27.3kg/m2. Data was also collected according to tumor stage, ER and PR status, age, chemotherapy, and endocrine treatment (typically, aromatase inhibitors or tamoxifen). The authors analyzed the data using multiple regression models.
A majority of the women had early stage ER+/PR+ tumors, for which they received chemotherapy and/or endocrine treatment; 17% were hormone receptor negative (ER-/PR-) and only 6% had detectable metastases at diagnosis. Diabetic women tended to be older and were more likely to have high BMI, ER-/PR- disease, and detectable metastases than non-diabetic patients.
After adjusting for other variables, women with ER+/PR+ disease who had high BMI levels (defined as over 27.3kg/m2) were found to have almost three times (2.9x) the risk of breast cancer-specific death than those with normal to overweight BMI levels (23.5-27.3 kg/m2). Breast cancer-specific mortality was also found to be more than double (2.6x) in women with high fasting blood glucose (defined as over 94 mg/dl) compared to those with glucose 84.1-94.0 mg/dl. Note that 94 mg/dl is not high enough to qualify as type 2 diabetes. The authors conclude that high blood glucose and high BMI are independently associated with increased risk of breast cancer-specific death in women with ER+/PR+ disease. Detection and correction of these factors in such women might improve prognosis, according to the authors.