Mammographic Density

Figure 1 is a composite of six mammographic images of the breast. These images illustrate that the breast has a wide range of appearance on mammography, associated with differences in composition. Radiographically the breast consists mainly of two component tissues: fibroglandular tissue and fat. Fibroglandular tissue is a mixture of fibrous connective tissue (the stroma) and the functional (or glandular) epithelial cells that line the ducts of the breast (the parenchyma). The remainder of the breast is fat. In terms of X-ray attenuation, fat is more radiolucent than fibroglandular tissue; thus, regions of fat appear darker on a transilluminated radiograph of the breast. Regions of brightness associated with fibroglandular tissue are referred to as mammographic density.

The hypothesis that breast cancer risk is associated with mammographic density was presented by Wolfe in the 1970s [2,3]. Wolfe developed a qualitative scale that classified the breast as being predominately composed of fat or as belonging to one of three categories representing increased mammo-graphic density associated with either the prominence of the ductal structures or diffuse areas of density. These categories were then related to the subsequent development of breast cancer.

Each of the images in Fig. 1 was selected as representative of one of the categories of a six-category classification (SCC) scheme that is quantitative for the proportion of the breast that appears as mammographically dense tissue. The six categories in this classification range from "no density" to "extensive density." This system, which is used subjectively in reader studies [4], represents an attempt to develop a single-variable scale for characterizing mammographic density that is more quantitative than the Wolfe grades.

Table 1 summarizes the results of a nested case-control study that related breast density classified according to SCC by radiologists with cancer incidence [4]. It illustrates the structure of a study used to quantify a risk factor. The table includes odds ratios (OR) as an approximation of the relative risk (RR) of disease, across categories of mammographic density. The OR is the ratio of the odds of being a case (having developed breast cancer) to being a control in each category relative to the odds in the lowest density category. This study demonstrated that any increased mammographic density is associated with an increased chance of developing cancer. Women (aged 40-59) with the most extensive density were found to be 5.3 times more likely to have been diagnosed with cancer relative to women with an absence of density. At

FIGURE 1 Mammographic images taken in the cranial-caudal projection illustrating a six-category classification (SCC) of mammographic density. Quantification is in terms of the percentage of the area of the breast that appears as mammographically dense tissue. The categories are defined as follows: A, NONE; B, (0,10]; C, (10,25]; D, (25,50]; E, (50,75]; F, (75,100]. Note that "]" indicates that the endpoint is included with the interval. Reprinted with permission from Byng JW, Boyd NF, Fishell E, et al. The quantitative analysis of mammographic densities. Physics in Medicine and Biology 1994; 39:1629-1638.

FIGURE 1 Mammographic images taken in the cranial-caudal projection illustrating a six-category classification (SCC) of mammographic density. Quantification is in terms of the percentage of the area of the breast that appears as mammographically dense tissue. The categories are defined as follows: A, NONE; B, (0,10]; C, (10,25]; D, (25,50]; E, (50,75]; F, (75,100]. Note that "]" indicates that the endpoint is included with the interval. Reprinted with permission from Byng JW, Boyd NF, Fishell E, et al. The quantitative analysis of mammographic densities. Physics in Medicine and Biology 1994; 39:1629-1638.

TABLE 1 Distribution of case and control subjects according to mammographie density in the Canadian National Breast Screening Study: unmatched, unadjusted analysis of radiologist-estimated densities"

Proportion of breast occupied by densities (%)

TABLE 1 Distribution of case and control subjects according to mammographie density in the Canadian National Breast Screening Study: unmatched, unadjusted analysis of radiologist-estimated densities"

Proportion of breast occupied by densities (%)

Age at entry to NBSS

None

(0, 10)

(10,25)

(25,50)

(50,75)

(75, 100)

Case

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment