Investigators have found that about 40% of postmenopausal hormone receptor–positive breast cancer cases may be linked to excess body fat, according to a recent study published by Cubelos-Fernández et al in the Journal of Epidemiology & Community Health.
Background
Using the widely used measure of body mass index (BMI), it has previously been estimated that 10% of postmenopausal hormone receptor–positive breast cancer cases may be attributed to excess weight. However, BMI may not be an accurate measure of body fat, particularly among older women, because the measure doesn’t account for age, sex, or ethnicity—indicating that the real impact of obesity on breast cancer risk has likely been underestimated.
Study Methods and Results
In the recent MCC-Spain study, the investigators compared the predictive accuracy of BMI with the Clínica Universidad de Navarra–Body Adiposity Estimator (CUN-BAE)—a validated measure of body fat that considers age and sex—in 1,033 postmenopausal White female patients with breast cancer and 1,143 patients without the disease who were matched on the basis of age, sex, and geographical region. The CUN-BAE categorizes body fat into four groups: less than 35%, 35% to 39.9%, 40% to 44.9%, and 45% and above. BMI classifies weight as: less than 25 kg/m2, 25 to 29.9 kg/m2, 30 to 34.9 kg/m2, and 35 kg/m2 and above.
The current study aimed to evaluate the environmental and genetic factors associated with colorectal, breast, gastric, and prostate cancers, as well as chronic lymphocytic leukemia, among patients aged 20 to 85 years. The patients were also quizzed on potentially influential risk factors: sociodemographics, lifestyle, and personal/family medical and reproductive histories. The investigators collected dietary information through a validated semistructured 140-item Food Frequency Questionnaire and gathered information on usual alcohol intake between the ages of 30 and 40 years using a self-administered questionnaire.
The investigators found that the average BMI was just over 26 in the comparison group and just over 27 in the breast cancer group, whereas the average CUN-BAE was just under 40% and nearly 40.5%, respectively.
A reference BMI below 25 was observed in 45% of those in the comparison group and 37% of the patients in the breast cancer group. A BMI of 30 or above, signifying obesity, was observed in 20% of those in the comparison group and in just over 24% of the patients in the breast cancer group. A reference CUN-BAE below 35% was observed in 20.5% of the patients in the comparison group and in 16% of those in the breast cancer group. A CUN-BAE of 40% or above was observed in just over 46% of those in the comparison group and in 53% of the patients in the breast cancer group.
A CUN-BAE of 45% or above was associated with more than double the risk of postmenopausal breast cancer compared with a CUN-BAE of below 35%. No similar trend was observed for BMI, prompting the investigators to estimate that 23% of breast cancer cases may be attributable to excess body fat using BMI, but 38% using the CUN-BAE.
Nonetheless, these differences were only apparent among patients with hormone receptor–positive breast cancer (n = 680), for which the estimated proportions attributable to excess body fat were 20% (BMI) and 42% (CUN-BAE).
Causal factors were unable to be established from the findings because the CUN-BAE formula was calculated from a sample of sedentary individuals, and the number of breast cancer cases that weren’t hormone receptor positive was low.
Conclusions
The findings could be crucial for planning effective prevention initiatives.
“The results of our study indicate that excess body fat is a significant risk factor for hormone receptor–positive breast cancer in postmenopausal women,” the study authors underscored. “Our findings suggest that the population impact could be underestimated when using traditional BMI estimates, and that more accurate measures of body fat—such as CUN-BAE—should be considered when estimating the cancer burden attributable to obesity in postmenopausal breast cancer,” they concluded.
Disclosure: For full disclosures of the study authors, visit jech.bmj.com.
