Table 3.
Age-adjusted and multivariable-adjusted risk of breast cancer by levels of lobular involution and parenchymal pattern of mammographic breast density*
| Characteristic | No. of women (%) | No. of women with breast cancer | No. of person-years of follow-up | Age adjusted† | Multivariable adjusted§ | Multivariable adjusted‖ | |||
| HR (95% CI) | Ptrend‡ | HR (95% CI) | Ptrend‡ | HR (95% CI) | Ptrend‡ | ||||
| Involution¶ | <.001 | .002 | .002 | ||||||
| Complete | 641 (24.0) | 28 | 7975 | 1.00# | 1.00# | 1.00# | |||
| Partial | 1666 (62.5) | 120 | 22 503 | 2.10 (1.37 to 3.23) | 1.62 (1.03 to 2.53) | 1.61 (1.03 to 2.53) | |||
| None | 359 (13.5) | 24 | 4895 | 2.96 (1.59 to 5.51) | 2.62 (1.40 to 4.92) | 2.62 (1.39 to 4.94) | |||
| Parenchymal pattern** | .002 | .018 | .022 | ||||||
| N1 | 555 (20.8) | 23 | 7255 | 1.00# | 1.00# | 1.00# | |||
| P1 | 378 (14.2) | 19 | 4779 | 1.19 (0.65 to 2.18) | 1.22 (0.66 to 2.24) | 1.23 (0.67 to 2.26) | |||
| P2 | 642 (24.1) | 56 | 8580 | 2.08 (1.28 to 3.37) | 1.96 (1.20 to 3.21) | 1.96 (1.20 to 3.21) | |||
| DY | 1091 (40.9) | 74 | 14 758 | 1.92 (1.19 to 3.10) | 1.70 (1.05 to 2.77) | 1.67 (1.03 to 2.73) | |||
Nested cohort study of women with benign breast disease (BBD) diagnosed between January 1, 1985, and December 31, 1991 at the Mayo Clinic. All analyses were done using the Cox proportional hazards model. CI = confidence interval; HR = hazard ratio.
Age-adjusted univariate analysis.
Ptrend values were calculated using two-sided Wald test for trend.
Multivariable analysis adjusting for age, BBD histology, body mass index (BMI), parity, menopause status, and family history.
Multivariable analysis adjusting for age, BBD histology, BMI, parity, menopause status and family history, and parenchymal pattern (for lobular involution) or lobular involution (for parenchymal pattern).
Extent of lobular involution was classified as none (0% lobules involuted), partial (1%–74% lobules involuted), and complete (≥75% lobules involuted).
Referent category in the Cox proportional hazards model.
Wolfe parenchymal pattern: N1—nondense, no ducts visible; P1—ductal prominence occupying less than a fourth of the breast; P2—prominent ductal pattern occupying more than a fourth of the breast; DY—homogenous, plaque-like areas of extreme density.