Table 2.
Mammographic features in tumor and nontumor side in cases and control subjects
| Mammographic features | Cases (n = 433) | Control subjects (n = 1732) | p Valuea |
|---|---|---|---|
| Percentage mammographic density on tumor side, median (IQR) | 23.0 (6.1–44.1) | 12.2 (2.4–32.8) | 4.0 × 10−10 |
| Percentage mammographic density on nontumor side, median (IQR) | 21.7 (5.1–43.4) | 12.5 (2.7–33.2) | 2.5 × 10−7 |
| Tumor vs. nontumor side, percentage mammographic density | 1.1 (7.8) | – | 3.4 × 10−3 |
| Number of microcalcifications on tumor side, mean (SD) | 6.1 (15.3) | 2.6 (13.1) | 4.0 × 10−20 |
| Number of microcalcifications on nontumor side, mean (SD) | 3.4 (13.0) | 2.6 (12.2) | 0.03 |
| Tumor vs. nontumor side, microcalcifications | 2.7 (17.9) | – | 1.9 × 10−3 |
| Number of masses on tumor side, mean (SD) | 0.77 (0.92) | 0.56 (0.76) | 8.4 × 10−6 |
| Number of masses on nontumor side, mean (SD) | 0.51 (0.75) | 0.55 (0.78) | 0.39 |
| Tumor vs. nontumor side, masses | 0.26 (1.1) | – | 9.2 × 10−3 |
| Individual absolute difference between breastsb | |||
| Percentage mammographic density, mean (SD) | 3.8 (4.0) | 3.1 (3.7) | 1.7 × 10−6 |
| Microcalcifications, mean (SD) | 2.9 (6.1) | 1.6 (5.7) | 4.0 × 10−16 |
| Number of masses, mean (SD) | 0.33 (0.42) | 0.28 (0.40) | 0.02 |
a p Values of median values were calculated with Wilcoxon rank-sum test. p Values of means were calculated with Student’s t test. Mediolateral oblique and craniocaudal view mammograms are used. The individual microcalcifications are within calcification cluster(s)
bAbsolute difference between the two breasts was calculated as the standard deviation SD of density of the left and right breasts for each woman