Table 2. Breast cancers and tumour characteristics at different reading strategies.
| Reading strategy | Single radiologist reading | Radiologist double-reading | Single radiologist reading and radiographer double-reading with referral of all positive readings | Radiologist double-reading followed by radiologist review of positive cases at radiographer double-reading | Double-reading by radiologists and radiographers with referral of all positive readings |
|---|---|---|---|---|---|
| Referral rate, % (95% CI) | 1.24 (1.17–1.31) | 1.36 (1.30–1.43) | 1.96 (1.87–2.04) | 1.48 (1.41–1.55) | 2.04 (1.95–2.12) |
| Mammographic abnormality, no. (%) | 1315 | 1448 | 2076 | 1570 | 2161 |
| Density | 877 (66.7) | 967 (66.8) | 1386 (66.8) | 1041 (66.3) | 1448 (67.0) |
| Microcalcifications | 257 (19.5) | 289 (20.0) | 447 (21.5) | 331 (21.1) | 464 (21.5) |
| Density with microcalcifications | 106 (8.1) | 114 (7.9) | 140 (6.7) | 116 (7.4) | 145 (6.7) |
| Architectural distortion | 44 (3.3) | 47 (3.2) | 62 (3.0) | 51 (3.2) | 64 (3.0) |
| Breast parenchyma asymmetry | 31 (2.4) | 31 (2.1) | 41 (2.0) | 31 (2.0) | 40 (1.9) |
| Breast cancers, no. | 492 | 528 | 579 | 564 | 592 |
| CDR, per 1,000 women (95% CI) | 4.64 (4.23–5.05) | 4.98 (4.55–5.40) | 5.46 (5.01–5.90) | 5.32 (4.88–5.75) | 5.58 (5.13–6.03) |
| Sensitivity, % (95% CI) | 63.9 (60.5–67.3) | 68.6 (65.3–71.9) | 75.2 (72.1–78.2) | 73.2 (70.1–76.4) | 76.9 (73.9–79.9) |
| Specificity, % (95% CI) | 99.2 (99.2–99.3) | 99.1 (99.1–99.2) | 98.6 (98.5–98.7) | 99.0 (99.0–99.1) | 98.5 (98.4–98.6) |
| PPV of referral, % (95% CI) | 37.4 (34.8–40.0) | 36.5 (34.0–38.9) | 27.9 (26.0–29.8) | 35.9 (33.6–38.3) | 27.4 (25.5–29.3) |
| Type of breast cancer, no. (%) | |||||
| DCIS | 80 (16.3) | 90 (17.0) | NA | 98 (17.4) | NA |
| Invasive | 412 (83.7) | 438 (83.0) | NA | 466 (82.6) | NA |
| T1a–c | 321 (77.9) | 342 (78.1) | NA | 366 (78.5) | NA |
| T2 | 88 (21.4) | 93 (21.2) | NA | 96 (20.6) | NA |
| Unknown | 3 (0.7) | 3 (0.7) | NA | 4 (0.9) | NA |
CI=confidence interval; CDR=cancer detection rate; DCIS=ductal carcinoma in situ; PPV=positive predictive value.
NA: several cancers were diagnosed as interval cancers or detected at subsequent screening. Consequently, exact tumour stages of these cancers at the time of the index screening examination are not available.