Table 2.
Breast cancer detection by ultrasound or mammography for categories of visually estimated breast density and participant age at time of screening across three annual screening rounds
| Screen characteristic | Screens with cancer | US sensitivity | Mammography sensitivity | Difference in sensitivity of US vs mammography | US but not mammography detections | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| No. cancers/ No. screens | (Incidence, %) | No. detected/ No. Cancers | (%) | No. detected/ No. Cancers | (%) | Estimate | P * | No. detected/ No. cancers | (%) | |
| Density, % | ||||||||||
| ≤25 | 1/128 | (0.8) | 0/1 | (0.0) | 0/1 | (0.0) | 0.0 | 1.00 | 0/1 | (0.0) |
| 26–40 | 17/710 | (2.4) | 9/17 | (52.9) | 11/17 | (64.7) | -11.8 | .73 | 3/17 | (17.6) |
| 41–60 | 36/2390 | (1.5) | 18/36 | (50.0) | 21/36 | (58.3) | -8.3 | .66 | 9/36 | (25.0) |
| 61–80 | 41/2890 | (1.4) | 22/41 | (53.7) | 18/41 | (43.9) | 9.8 | .54 | 14/41 | (34.1) |
| >80 | 16/1352 | (1.2) | 9/16 | (56.3) | 9/16 | (56.3) | 0.0 | 1.00 | 6/16 | (37.5) |
| P trend † | --- | --- | --- | .65 | --- | .38 | .39 | --- | --- | .11‡ |
| Unknown | 0/3 | (0) | 0/0 | (NA) | 0/0 | (NA) | NA | NA | 0/0 | (NA) |
| Age, y | ||||||||||
| <40 | 2/289 | (0.7) | 1/2 | (50.0) | 2/2 | (100) | -50.0 | 1.00 | 0/2 | (0.0) |
| 40–49 | 16/1538 | (1.0) | 8/16 | (50.0) | 7/16 | (43.8) | 6.3 | 1.00 | 6/16 | (37.5) |
| 50–69 | 79/4916 | (1.6) | 39/79 | (49.4) | 42/79 | (53.2) | -3.8 | .76 | 20/79 | (25.3) |
| >69 | 14/730 | (1.9) | 10/14 | (71.4) | 8/14 | (57.1) | 14.3 | .75 | 6/14 | (42.9) |
| P trend † | --- | --- | --- | .27 | --- | .69 | .68 | --- | --- | .68‡ |
* Two-sided Exact McNemar’s test. NA = not applicable; US = ultrasound.
† Using two-sided Wald test for the factor’s coefficient of the generalized estimating equation model accounting for possible correlation between assessments of the same patients (proc genmod, SAS, v. 9.3, Cary, NC). The test for trend was performed for the two lowest categories grouped together; conclusions remain the same with for the test for trend with presented categories.
‡ Care must be taken in interpreting P values for “US but not mammography detections” because of post hoc nature of the analyses and sparse data.