Table 3a.
(1992–2011) Relative risks (RRs) with 95% confidence intervals for invasive breast cancer overall, oestrogen receptor positive (ER+) and ER negative (ER–) breast cancers by reproductive variables among nulliparous and parous women born in 1935 or later
| Exposure | Overall | ER + | ER– | P-value for homogeneity ER ± |
|---|---|---|---|---|
| Nulliparous cases (n = 5317) and parous cases (n = 40 469) | ||||
| Number of cases | n = 45 786 | n = 33 631 | n = 9123 | |
| Parity | RR (95% CI) | RR (95% CI) | RR (95% CI) | |
| Nulliparous | 1.0 (reference) | 1.0 (reference) | 1.0 (reference) | |
| Parous | 0.90 (0.88, 0.93) | 0.88 (0.85, 0.91) | 1.04 (0.98, 1.11) | |
| p-heterogeneity | <0.001 | <0.001 | 0.22 | <0.001 |
| Parous cases (n = 40 469) | ||||
| Number of cases | n = 40 469 | n = 29 738 | n = 8114 | |
| Number of live births | RR (95% CI) | RR (95% CI) | RR (95% CI) | |
| 1 | 1.0 (reference) | 1.0 (reference) | 1.0 (reference) | |
| 2 | 0.97 (0.94, 0.99) | 0.94 (0.91, 0.97) | 1.07 (1.01, 1.14) | |
| 3 | 0.88 (0.85, 0.91) | 0.87 (0.84, 0.90) | 0.95 (0.88, 1.02) | |
| 4+ | 0.75 (0.71, 0.78) | 0.71 (0.67, 0.75) | 0.87 (0.79, 0.97) | |
| p-trend | <0.001 | <0.001 | <0.001 | <0.001 |
| p-heterogeneity | <0.001 | <0.001 | <0.001 | |
| AFLB (years) | RR (95% CI) | RR (95% CI) | RR (95% CI) | |
| 12–19 | 1.01 (0.98, 1.04) | 1.00 (0.97, 1.04) | 1.07 (1.00, 1.14) | |
| 20–24 | 1.0 (reference) | 1.0 (reference) | 1.0 (reference) | |
| 25–29 | 1.09 (1.06, 1.11) | 1.10 (1.07, 1.13) | 1.04 (0.98, 1.09) | |
| 30–34 | 1.22 (1.18, 1.27) | 1.25 (1.20, 1.30) | 1.13 (1.04, 1.22) | |
| 35+ | 1.18 (1.11, 1.26) | 1.22 (1.14, 1.31) | 0.99 (0.85, 1.16) | |
| p-trend | <0.001 | <0.001 | 0.52 | <0.001 |
| p-heterogeneity | <0.001 | <0.001 | 0.015 | |
| Nulliparous cases (n = 5317) and uniparous cases (n = 7951) | ||||
| Number of cases | n = 13 268.00 | n = 9834 | n = 2498 | |
| AFLB (years) | RR (95% CI) | RR (95% CI) | RR (95% CI) | |
| 12–19 | 0.90 (0.83 0.98) | 0.88 (0.80, 0.97) | 1.03 (0.85, 1.24) | |
| 20–24 | 0.92 (0.88, 0.96) | 0.92 (0.87, 0.98) | 0.95 (0.85, 1.07) | |
| 25–29 | 0.98 (0.94, 1.03) | 1.00 (0.94, 1.05) | 1.00 (0.89, 1.11) | |
| 30–34 | 1.09 (1.03, 1.15) | 1.08 (1.02, 1.15) | 1.18 (1.04, 1.33) | |
| 35+ | 1.05 (0.97, 1.14) | 1.08 (0.99, 1.18) | 0.95 (0.79, 1.16) | |
| Nulliparous | 1.0 (reference) | 1.0 (reference) | 1.0 (reference) | |
| p-trend | <0.001 | 0.003 | 0.87 | 0.65 |
| p-heterogeneity | <0.001 | <0.001 | 0.35 | |
Cases with unknown ER status (n = 3032) were excluded from the ER-specific analyses. AFLB, age at first live birth; P-value for homogeneity is based on comparison ER± subtypes.