Table 4.
Multivariable adjusted* odds ratio (OR) and 95% confidence interval (CI) for triple negative and luminal A breast cancer associated with reproductive history by age
| Younger (age 35–44 years) | Older (age 45–64 years) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| No. controls |
No. triple negative |
No. luminal A |
OR (95% CI) of triple negative |
OR (95% CI) of luminal A |
No. controls | No. triple negative |
No. luminal A |
OR (95% CI) of triple negative |
OR (95% CI) of luminal A |
|
| Number of full-term pregnancies | ||||||||||
| Never pregnant | 70 | 19 | 26 | Reference | Reference | 106 | 9 | 57 | Reference | Reference |
| 1 | 140 | 24 | 40 | 0.62 (0.31–1.23) | 0.81 (0.45–1.45) | 174 | 31 | 69 | 1.77 (0.80–3.91) | 0.80 (0.52–1.25) |
| 2 | 219 | 50 | 64 | 0.89 (0.48–1.64) | 0.84 (0.49–1.45) | 355 | 56 | 123 | 1.70 (0.81–3.58) | 0.68 (0.46–1.01) |
| 3 | 127 | 29 | 30 | 0.89 (0.45–1.74) | 0.67 (0.36–1.25) | 264 | 27 | 85 | 1.15 (0.51–2.55) | 0.66 (0.43–1.00) |
| ≥4 | 76 | 16 | 15 | 0.76 (0.35–1.67) | 0.56 (0.26–1.17) | 326 | 47 | 89 | 1.48 (0.68–3.21) | 0.56 (0.36–0.86) |
| Trend p-value | 0.87 | 0.09 | 0.77 | 0.006 | ||||||
| Test for homogeneity of trends P-value | 0.16 | 0.15 | ||||||||
| Only non-full-term pregnancy |
89 | 16 | 22 | 0.62 (0.29–1.30) | 0.66 (0.34–1.27) | 69 | 11 | 25 | 1.61 (0.63–4.13) | 0.67 (0.38–1.19) |
| Age at first full-term pregnancy†, years | ||||||||||
| ≤19 | 163 | 31 | 33 | Reference | Reference | 420 | 72 | 106 | Reference | Reference |
| 20–24 | 154 | 39 | 51 | 1.40 (0.80–2.43) | 1.61 (0.96–2.69) | 460 | 52 | 144 | 0.73 (0.48–1.11) | 1.10 (0.81–1.51) |
| 25–29 | 129 | 25 | 41 | 1.14 (0.59–2.20) | 1.50 (0.84–2.68) | 150 | 20 | 83 | 0.91 (0.50–1.65) | 1.95 (1.31–2.90) |
| ≥30 | 116 | 24 | 24 | 1.43 (0.66–3.09) | 0.92 (0.45–1.90) | 89 | 17 | 33 | 1.41 (0.71–2.80) | 1.22 (0.71–2.09) |
| Trend p-value | 0.48 | 0.95 | 0.66 | 0.04 | ||||||
| Test for homogeneity of trends P-value | 0.58 | 0.35 | ||||||||
| Duration of breastfeeding†, months | ||||||||||
| Never | 180 | 46 | 60 | Reference | Reference | 532 | 85 | 180 | Reference | Reference |
| <1 | 61 | 14 | 14 | 0.83 (0.41–1.67) | 0.66 (0.34–1.31) | 141 | 24 | 51 | 1.11 (0.67–1.84) | 1.04 (0.71–1.52) |
| 1–6 | 144 | 28 | 36 | 0.63 (0.36–1.11) | 0.61 (0.37–1.02) | 190 | 26 | 56 | 0.86 (0.53–1.41) | 0.73 (0.51–1.04) |
| 7–23 | 123 | 20 | 31 | 0.45 (0.24–0.87) | 0.60 (0.34–1.05) | 179 | 16 | 60 | 0.60 (0.34–1.07) | 0.86 (0.60–1.23) |
| ≥24 | 54 | 11 | 8 | 0.55 (0.24–1.28) | 0.35 (0.15–0.86) | 77 | 10 | 19 | 0.82 (0.39–1.72) | 0.69 (0.40–1.21) |
| Trend p-value | 0.02 | 0.01 | 0.14 | 0.09 | ||||||
| Test for homogeneity of trends P-value | 0.97 | 0.80 | ||||||||
Note: Triple negative = ER−/PR−/HER2−, Luminal A = ER+ or PR+ plus HER2−.
*
Adjusted for study site, race, education, age, family history of breast cancer, age at menarche, menopausal status, body mass index.
†
Also adjusted for parity and mutually adjusted for age at first full-term pregnancy and duration of breastfeeding among parous women.