Table 4.
Associations of percent mammographic breast density (PD) with breast cancer risk in a subgroup of women with atypical hyperplasia
| Characteristic | No. Women | Person Years | Observed Events | Expected Events | SIR (95% CI) | p-valuea |
|---|---|---|---|---|---|---|
| Overall | 212 | 2469 | 32 | 10.15 | 3.15 (2.16, 4.45) | |
| Percent Density | 0.76 | |||||
| 0-10% | 59 | 688 | 8 | 3.15 | 2.54 (1.10, 5.00) | |
| 11-25% | 69 | 777 | 12 | 3.20 | 3.75 (1.94, 6.55) | |
| 26-50% | 76 | 900 | 10 | 3.41 | 2.94 (1.41, 5.40) | |
| 51 + % | 8 | 104 | 2 | 0.40 | 4.98 (0.60, 17.92) |
Standardized incidence ratios and corresponding 95% confidence intervals, comparing the observed number of breast cancer events to those expected based on incidence rates from Iowa SEER data
Analyses account for the effects of age and calendar period
a P-value, test of heterogeneity in SIRs