Table 2.
Number of breast cancers, person-years, rates, and RRs by demographic, reproductive, and anthropometric factors.
| Breast Cancers* | Woman-Years | Crude Rate | RR** | 95% CI | |
|---|---|---|---|---|---|
| Attained Age | |||||
| 55–59 | 274 | 63,088 | 434.31 | 1.00 | Ref. |
| 60–64 | 608 | 108,640 | 559.65 | 1.36 | 1.18–1.57 |
| 65–69 | 582 | 104,433 | 557.30 | 1.44 | 1.24–1.67 |
| 70–74 | 434 | 79,134 | 548.44 | 1.48 | 1.26–1.73 |
| 75+ | 187 | 34,419 | 543.30 | 1.47 | 1.21–1.79 |
| Race | |||||
| White | 1,854 | 345,926 | 535.95 | 1.00 | Ref. |
| African-American | 89 | 19,765 | 450.29 | 1.05 | 0.84–1.32 |
| Asian/Pacific Islander | 111 | 17,230 | 644.23 | 1.14 | 0.86–1.51 |
| Other/unknown | 31 | 6,793 | 456.35 | 0.92 | 0.64–1.32 |
| Family history of breast cancer | |||||
| No | 1696 | 336,410 | 504.15 | 1.00 | Ref. |
| Yes | 389 | 53,304 | 729.78 | 1.44 | 1.29–1.60 |
| Number of Live Births | |||||
| 0 | 240 | 35,545 | 675.20 | 1.00 | Ref. |
| 1 | 160 | 28,296 | 565.45 | 0.70 | 0.55–0.89 |
| 2 | 524 | 88,510 | 592.02 | 0.76 | 0.62–0.92 |
| 3 | 526 | 96,163 | 546.99 | 0.75 | 0.62–0.91 |
| 4 | 331 | 66,673 | 496.45 | 0.72 | 0.59–0.88 |
| 5+ | 301 | 73,888 | 407.37 | 0.65 | 0.53–0.80 |
| Age at First Birth | |||||
| None | 240 | 35,545 | 675.20 | 1.00 | Ref. |
| < 20 | 267 | 62,165 | 429.50 | 0.68 | 0.53–0.86 |
| 20–24 | 901 | 181,709 | 495.85 | 0.74 | 0.59–0.91 |
| 25–29 | 471 | 80,523 | 584.93 | 0.83 | 0.66–1.03 |
| 30–34 | 148 | 20,822 | 710.79 | 1.03 | 0.81–1.31 |
| 35+ | 47 | 6,894 | 681.75 | 1.02 | 0.74–1.41 |
| Age at Menarche | |||||
| < 12 years | 457 | 76,987 | 593.61 | 1.00 | Ref. |
| 12–13 years | 1099 | 209,082 | 525.63 | 0.86 | 0.77–0.97 |
| 14–15 years | 439 | 84,595 | 518.94 | 0.85 | 0.74–0.97 |
| ≥ 16 years | 88 | 17,874 | 492.34 | 0.81 | 0.65–1.02 |
| Age at Menopause | |||||
| < 45 years | 123 | 25,254 | 487.05 | 1.00 | Ref. |
| 45–49 years | 340 | 64,113 | 530.31 | 1.07 | 0.87–1.31 |
| 50–54 years | 700 | 126,080 | 555.20 | 1.12 | 0.92–1.35 |
| 55+ years | 211 | 32,192 | 655.44 | 1.29 | 1.03–1.62 |
| Surgical menopause | 574 | 122,386 | 469.01 | 0.84 | 0.69–1.02 |
| Radiation/medication | 94 | 12,061 | 779.37 | 1.32 | 1.01–1.74 |
| Menopausal hormone therapy use | |||||
| Never | 571 | 134,329 | 425.08 | 1.00 | Ref. |
| Former | 280 | 64,773 | 432.28 | 1.02 | 0.88–1.18 |
| Current, < 5 years | 372 | 61,931 | 600.67 | 1.44 | 1.26–1.66 |
| Current, ≥ 5 years | 847 | 125,006 | 677.57 | 1.67 | 1.49–1.87 |
| Weight (kg) | |||||
| < 60 | 437 | 82,961 | 526.75 | 1.00 | Ref. |
| 60 – 64.9 | 310 | 59,068 | 524.82 | 1.03 | 0.86–1.19 |
| 65 – 69.9 | 311 | 56,091 | 554.46 | 1.18 | 0.97–1.30 |
| 70 – 74.9 | 257 | 49,325 | 521.03 | 1.08 | 0.92–1.26 |
| 75 – 79.9 | 267 | 47,072 | 567.22 | 1.21 | 1.03–1.42 |
| ≥ 80 | 486 | 91,892 | 528.88 | 1.20 | 1.04–1.38 |
| Height (m) | |||||
| < 1.60 | 527 | 101,460 | 519.42 | 1.00 | Ref. |
| 1.60 – 1.64 | 605 | 117,236 | 516.05 | 1.01 | 0.89–1.13 |
| 1.65 – 1.69 | 561 | 102,205 | 548.90 | 1.06 | 0.94–1.20 |
| ≥ 1.70 | 385 | 66,707 | 577.15 | 1.11 | 0.97–1.27 |
| BMI (kg/m2) | |||||
| < 18.5 | 25 | 5,135 | 486.85 | 0.88 | 0.59–1.32 |
| 18.5 – 24.9 | 848 | 154,447 | 549.06 | 1.00 | Ref. |
| 25 – 29 | 712 | 133,799 | 532.14 | 1.06 | 0.95–1.17 |
| 30 – 34.9 | 305 | 59,109 | 516.00 | 1.10 | 0.97–1.26 |
| ≥ 35 | 173 | 32,478 | 532.67 | 1.21 | 1.02–1.43 |
* Includes confirmed invasive cancers, confirmed in situ lesions, and self-reported cancers.
** Adjusted for attained age, screening center, age at menarche, age at menopause, family history of breast cancer, benign breast disease, height, and menopausal hormone therapy (all in categories as shown in the table), plus combined age at first birth and parity (nulliparous or first birth after 35 years, first birth before age 25, first birth 25–34 years, or unknown) and calendar time (5/31/1993 – 5/31/1995, 6/1/1995 – 5/31/1997, 6/1/1997 – 5/31/1999, 6/1/1999 – 5/31/2001, and 6/1/2001 – 5/31/2003). RRs for age at first birth and parity were adjusted for the other factor.
Not shown are unknown parity (3 breast cancers and 638 person-years), age at first birth (11 breast cancers and 2,635 person-years), age at menarche (2 breast cancers and 1,177 person-years), age at or type of menopause (43 breast cancers and 7,628 person-years), menopausal hormone therapy use (15 breast cancers and 3,676 person-years), weight (17 breast cancers and 3,304 person-years), height (7 breast cancers and 2,107 person-years), and BMI (22 breast cancers and 4,747 person-years).