Measurements of Breast Density: No Ratio for a Ratio

Abstract

Breast density, as visible on mammograms, is generally assessed as the occupied percentage of the breast and is a risk factor for breast cancer. Various studies have looked into the causation and alteration of relative density but the relation of a determinant with a relative measure does not allow a direct etiologic interpretation. It was our goal to compare the effects of known determinants on relative density and the absolute amounts of dense and nondense tissues. We measured the absolute and relative densities in a population of 418 postmenopausal women participating in a breast cancer screening program. The occupied surface area was calculated after manually tracing the contours of the tissues on digitized mammograms. Information on determinants was available through physical examination and questionnaires. Data were analyzed by multivariate linear regression. Age and parity were found to decrease the amount of dense tissue and the ages at menarche and menopause were found to increase it (R 2 = 13%). The amount of nondense tissue was increased by higher body mass index (BMI), age, and parity (R 2 = 43%). Relative density was affected by a combination of these factors (R 2 = 29%) with directionalities of effects that are comparable to those of dense tissue. However, the magnitudes of these effects were the resultant of the effects on dense and nondense tissues. The influence of BMI on relative density was completely due to an effect on nondense tissue. Although relative density is a relevant prognostic factor, inferences about the etiology of breast density should be made on the basis of absolute measures. (Cancer Epidemiol Biomarkers Prev 2005; 1411(11):2634

A case‐control study to assess the impact of mammographic density on breast cancer risk in women aged 40–49 at intermediate familial risk

“…Breast area of nondense tissue has been suggested as a proxy for body fat/weight. 24 In our data, absolute nondense area was negatively correlated with absolute dense area. In addition, the significance of absolute dense area as a predictor was increased after the model was adjusted for absolute nondense area.…”

“…Absolute nondense area has been shown to be correlated with weight and body fat in premenopausal women, 38 and with BMI in postmenopausal women 24 in cross-sectional studies, and with weight (and BMI) in both pre-and postmenopausal women in an age-and centre-matched case-control study. 17 Adjusting for BMI in the case-control study of Pettersson et al 23 only explained a small fraction of the association between absolute nondense area and decreased risk of breast cancer.…”

“…18,21,23 In addition, some studies have reported absolute dense area to be a better predictor of breast cancer risk than percent density. 24,25 In this article, we report on the effect of MD (measured both in relative and absolute terms) on risk of breast cancer in a case-control study of young women at moderately increased risk of breast cancer due to a family history of the disease.…”

High-Density Lipoprotein-Cholesterol, Daily Estradiol and Progesterone, and Mammographic Density Phenotypes in Premenopausal Women

“…Of note, absolute mammographic density, as compared with percent mammographic density, may be less confounded by body fat (17,18). However, it is unclear whether absolute mammographic density, compared with percent mammographic density, is a more suitable marker of breast cancer development, when studying factors such as variations in HDL-C levels, associated with metabolic syndrome (15,19,20).…”

Does Breast Size Modify the Association between Mammographic Density and Breast Cancer Risk?

“…The absolute amount of dense mammographic tissue, potentially reflecting the number of epithelial cells at risk, intuitively appears as a plausible explanation for the association between mammographic density and breast cancer risk. However, although absolute mammographic density has also been associated with breast cancer (2,3,7), percent mammographic density, that is, the ratio of the dense area to the total area of the breast as visualized by the mammogram, has been the most commonly used mammographic density measurement in relation to breast cancer risk (8). Contrary to absolute density, however, the measure of percent density does not specify the amount of dense tissue involved.…”