Table 1.
Association between ever breastfeeding and breast cancer risk by receptor status
| Receptor status | No. of studies | Relative risk/odds ratio (95% CI) | I2 statistics (%) | P for heterogeneity |
|---|---|---|---|---|
| ER−/PR− | ||||
| Cohort | 7 | 0.84 (0.72–0.97) | 50 | 0.06 |
| Adjusteda | 3 | 0.88 (0.74–1.06) | 42 | 0.18 |
| Only parous women | 6 | 0.88 (0.76–1.02) | 39 | 0.15 |
| Adjusteda, only parous | 3 | 0.88 (0.74–1.06) | 42 | 0.18 |
| Case–control | 13 | 0.76 (0.67–0.86) | 59 | 0.004 |
| Adjusteda | 5 | 0.89 (0.80–0.99) | 0 | 0.83 |
| Only parous women | 9 | 0.77 (0.65–0.91) | 55 | 0.02 |
| Adjusteda, only parous | 3 | 0.91 (0.79–1.04) | 0 | 0.94 |
| All, adjusteda | 8 | 0.89 (0.82–0.97) | 0 | 0.66 |
| All, only parous women | 15 | 0.81 (0.73–0.91) | 51 | 0.01 |
| All, adjusteda, only parous | 6 | 0.90 (0.82–0.99) | 0 | 0.61 |
| Triple negative | ||||
| Cohort | 3 | 0.73 (0.62–0.87) | 0 | 0.43 |
| Adjusteda | 1 | 0.81 (0.62–1.04) | – | – |
| Only parous women | 2 | 0.76 (0.53–1.08) | 15 | 0.28 |
| Adjusteda, only parous | 1 | 0.81 (0.62–1.04) | – | – |
| Case–control | 9 | 0.73 (0.64–0.84) | 12 | 0.34 |
| Adjusteda | 2 | 0.75 (0.61–0.93) | 0 | 0.67 |
| Only parous women | 7 | 0.71 (0.59–0.85) | 26 | 0.23 |
| Adjusteda, only parous | 2 | 0.75 (0.61–0.93) | 0 | 0.67 |
| All, adjusteda | 3 | 0.78 (0.66–0.91) | 0 | 0.83 |
| All, only parous women | 9 | 0.72 (0.63–0.84) | 17 | 0.29 |
| All, adjusteda, only parous | 3 | 0.78 (0.66–0.91) | 0 | 0.83 |
| ER+/PR+ | ||||
| Cohort | 4 | 1.00 (0.90–1.10) | 54 | 0.09 |
| Adjusteda | 2 | 1.06 (0.98–1.15) | 0 | 0.55 |
| Only parous women | 4 | 1.00 (0.90–1.10) | 54 | 0.09 |
| Adjusteda, only parous | 2 | 1.06 (0.98–1.15) | 0 | 0.55 |
| Case–control | 7 | 0.86 (0.79–0.92) | 36 | 0.15 |
| Adjusteda | 4 | 0.88 (0.78–0.99) | 43 | 0.16 |
| Only parous women | 4 | 0.80 (0.75–0.86) | 0 | 0.84 |
| Adjusteda, only parous | 2 | 0.82 (0.73–0.91) | 0 | 0.47 |
| All, adjusteda | 6 | 0.95 (0.85–1.06) | 68 | 0.008 |
| All, only parous women | 8 | 0.89 (0.80–0.99) | 77 | <0.001 |
| All, adjusteda, only parous | 4 | 0.94 (0.79–1.12) | 80 | 0.002 |
| ER+ and/or PR+ | ||||
| Cohort | 7 | 0.97 (0.88–1.07) | 78 | <0.001 |
| Adjusteda | 3 | 1.04 (0.98–1.10) | 0 | 0.56 |
| Only parous women | 5 | 1.00 (0.92–1.09) | 43 | 0.14 |
| Adjusteda, only parous | 2 | 1.04 (0.95–1.14) | 15 | 0.28 |
| Case–control | 18 | 0.82 (0.76–0.89) | 69 | <0.001 |
| Adjusteda | 5 | 0.88 (0.76–1.02) | 72 | 0.006 |
| Only parous women | 12 | 0.83 (0.74–0.92) | 70 | <0.001 |
| Adjusteda, only parous | 3 | 0.89 (0.71–1.11) | 75 | 0.02 |
| All, adjusteda | 8 | 0.95 (0.87–1.05) | 75 | <0.001 |
| All, only parous women | 17 | 0.88 (0.81–0.97) | 78 | <0.001 |
| All, adjusteda, only parous | 5 | 0.97 (0.85–1.11) | 77 | 0.002 |
aResults adjusted at least for age, body mass index, parity, and family history of breast cancer.
ER, estrogen receptor; ER−/PR−, negative for both ER and PR; ER+/PR+, positive for both ER and PR; ER+ and/or PR+, positive for either estrogen or progesterone receptor or both; PR, progesterone receptor.