Positive predictive value of specific mammographic findings according to reader and patient variables

Abstract

Purpose: To evaluate the risk of cancer (positive predictive value [PPV]) associated with specific findings (mass, calcifications, architectural distortion, asymmetry) in mammographic examinations with abnormal results, to determine the distribution of these findings in examinations in which the patients received a diagnosis of cancer and examinations in which the patients did not, and to analyze PPV variation according to radiologist and patient factors.

Materials and methods: HIPAA-compliant institutional review board approval was obtained. PPV of mammographic findings was evaluated in a prospective cohort of 10,262 women who underwent 10,641 screening or diagnostic mammographic examinations with abnormal results between January 1998 and December 2002 in the San Francisco Mammography Registry. The cohort was linked with the Surveillance Epidemiology and End Results program to determine cancer status among these women. PPVs were calculated for each finding and were stratified according to patient characteristics, cancer type, and radiologist reader.

Results: Cases of breast cancer (n = 1552) were identified (invasive, n = 1287; ductal carcinoma in situ, n = 270); in five, both kinds of breast cancer were recorded. Overall, of the number of interpretations, masses were most frequently noted in 56%, followed by calcifications in 29%, asymmetry in 12%, and architectural distortion in 4%. Masses, calcifications, architectural distortion, and developing asymmetry demonstrated similar PPVs in screening examinations (9.7%, 12.7%, 10.2%, and 7.4%, respectively), whereas one-view-only and focal asymmetry demonstrated lower PPVs (3.6% and 3.7%, respectively) and were a frequent reason for an abnormal result (42%). Overall, one (5%) in 20 invasive cancers was identified with asymmetry, one (6%) in 16 invasive cancers was identified with architectural distortion, one (21%) in five invasive cancers was identified with calcifications, and two (68%) in three invasive cancers were identified with a mass.

Conclusion: Five percent of invasive cancers were identified with asymmetry, and asymmetry is more weakly associated with cancer in screening examinations than are mass, calcifications, and architectural distortion.

Figure 1:

Graph shows percentage of screening mammographic examinations with specific mammographic findings among women with cancer (true-positive results) and among women without cancer (false-positive results). Asymmetry represents 26% of false-positive results and 10% of true-positive results, compared with other findings that are more prevalent in true-positive results than in false-positive results. Sample sizes (n) refer to number of mammographic examinations.

Figure 2:

Graph shows relative efficiency of each finding among all mammograms, plotting finding-specific percentage of true-positive results versus finding-specific percentage of false-positive results. The steeper the line, the more predictive the finding is of cancer. Asymmetry is the least predictive finding.

Figure 3:

Graph shows finding-specific PPV for invasive cancer among screening mammographic examinations for individual high-volume radiologist readers. Asymmetry demonstrated lowest mean (2.3%) and median (0.5%) of all findings. Both architectural distortion and asymmetry demonstrated more skewedness than mass and calcifications, as demonstrated by greater discrepancy between their median and mean.