Obesity is associated with a larger tumor size at the time of breast cancer diagnosis compared with women of normal weight . The poor prognosis of breast cancer in obese women may reflect delayed diagnosis, as it may not be physically possible to detect small tumors in the large breasts of obese women, and there are data to suggest a preponderance of impalpable breast cancers in obese women .
Markers of aggressive tumors
Breast tumors in obese women are more likely to possess markers of high cellular proliferation, such as a high S-phase fraction, high histological grade, and high mitotic cell count, compared with those in thinner women . In addition, obesity is associated with an increased risk of invasive but not noninvasive cancer, suggesting that metabolic abnormalities accompanying obesity may activate proliferation, leading to the invasive phenotype .
Weight gain of 10 kg after the age of 18 years is associated with a twofold increase in the risk of developing breast cancer, which is more likely to be stage II than first breast cancers in women of normal weight . The incidence of axillary lymph node involvement increases with body weight and BMI, particularly in women with estrogen receptor (ER)-positive tumors . Obese women with ER-positive tumors have been found to have a 66% chance of nodal involvement, which is twice as high as that in thinner women (33%) [39,40].
Hormone receptor status
The association between obesity and hormone receptor status in breast cancer is complex.
However, studies have reported that obesity is more frequently associated with tumors that are ER- and progesterone receptor-negative .
Amtul R Carmichael, MD
Russells Hall Hospital, Dudley, UK