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Table 2 Multivariable-adjusteda hazard ratios (HRs) and 95% confidence intervals for breast cancer overall and by ER status in relation to parity and breastfeeding: Nurses’ Health Study (1976–2012) and Nurses’ Health Study II (1989–2013)

From: Parity, breastfeeding, and breast cancer risk by hormone receptor status and molecular phenotype: results from the Nurses’ Health Studies

 

All

ER+

ER−

Phet by

 

Cases

PY

HR (95% CI)

Cases

PY

HR (95% CI)

Cases

PY

HR (95% CI)

subtype

Parous

 Nulliparous

1498

742,502

1 (ref.)

979

742,976

1 (ref.)

209

743,672

1 (ref.)

 

 Parous

10,954

4,540,107

0.84 (0.80–0.89)

7256

4,543,555

0.82 (0.77–0.88)

1769

4,548,669

0.98 (0.84–1.13)

0.03

Breastfeeding

 Never breastfed (parous + nulliparous)

5101

2,100,966

1 (ref.)

3271

2,102,676

1 (ref.)

835

2,104,928

1 (ref.)

 

 Ever breastfed

7351

3,181,643

0.94 (0.91–0.98)

4964

3,183,855

0.99 (0.94–1.04)

1143

3,187,412

0.83 (0.75–0.92)

0.002

 ≤ 6 months

3242

1,255,908

0.93 (0.88–0.97)

2177

1,256,886

0.96 (0.90–1.01)

517

1,258,482

0.84 (0.75–0.95)

 

 7–11 months

1203

535,074

0.96 (0.90–1.03)

819

535,428

1.03 (0.95–1.11)

180

535,998

0.81 (0.68–0.95)

 

 ≥ 12 months

2906

1,390,661

0.96 (0.91–1.01)

1968

1,391,541

1.02 (0.96–1.09)

446

1,392,932

0.83 (0.73–0.94)

 
   

Ptrend = 0.72

  

Ptrend = 0.22

  

Ptrend = 0.05

0.02

Parity/breastfeeding

 Nulliparous

1498

742,502

1 (ref.)

979

742,976

1 (ref.)

209

743,672

1 (ref.)

 

 Parous women, never breastfed

3603

1,358,464

0.88 (0.83–0.94)

2292

1,359,700

0.83 (0.77–0.90)

626

1,361,257

1.11 (0.94–1.31)

< 0.001b

 1 child

518

210,088

0.92 (0.83–1.02)

332

210,263

0.88 (0.78–1.00)

91

210,483

1.15 (0.90–1.48)

0.002c

 2 children

1386

516,819

0.93 (0.86–1.00)

870

517,287

0.86 (0.78–0.94)

250

517,868

1.20 (0.99–1.45)

 

 ≥ 3 children

1699

631,558

0.81 (0.76–0.87)

1090

632,150

0.77 (0.70–0.84)

285

632,906

1.03 (0.85–1.25)

 

 Parous women, ever breastfed

7351

3,181,643

0.83 (0.78–0.88)

4964

3,183,855

0.82 (0.76–0.88)

1143

3,187,412

0.92 (0.79–1.08)

 

 1 child

666

313,938

0.95 (0.86–1.04)

437

314,149

0.93 (0.83–1.04)

97

314,457

0.97 (0.76–1.23)

 

 2 children

2493

1,166,539

0.85 (0.79–0.91)

1694

1,167,283

0.85 (0.78–0.92)

362

1,168,492

0.87 (0.73–1.03)

 

 ≥3 children

4192

1,701,166

0.79 (0.74–0.84)

2833

1,702,423

0.78 (0.72–0.84)

684

1,704,463

0.95 (0.81–1.12)

 

Among parous women

 Parityd

  1 child

1184

524,026

1 (ref.)

769

524,412

1 (ref.)

188

524,940

1 (ref.)

 

  2 children

3879

1,683,357

1.02 (0.95–1.09)

2564

1,684,570

1.02 (0.94–1.11)

612

1,686,360

1.02 (0.86–1.21)

 

  3 children

3165

1,259,779

1.03 (0.96–1.10)

2120

1,260,791

1.03 (0.94–1.13)

502

1,262,311

1.06 (0.88–1.27)

 

  ≥ 4 children

2726

1,072,945

0.92 (0.85–1.00)

1803

1,073,782

0.91 (0.82–1.00)

467

1,075,059

1.08 (0.89–1.31)

 
   

Ptrend = 0.0001

  

Ptrend = 0.0001

  

Ptrend = 0.43

0.02

 Breastfeedingd

  Never breastfed

3603

1,358,464

1 (ref.)

2292

1,359,700

1 (ref.)

626

1,361,257

1 (ref.)

 

  Ever breastfed

7351

3,181,643

0.95 (0.91–0.99)

4964

3,183,855

0.99 (0.94–1.05)

1143

3,187,412

0.82 (0.74–0.91)

< 0.001

  ≤ 6 months

3242

1,255,908

0.93 (0.89–0.98)

2177

1,256,886

0.96 (0.91–1.02)

517

1,258,482

0.84 (0.75–0.95)

 

  7–11 months

1203

535,074

0.95 (0.89–1.02)

819

535,428

1.02 (0.94–1.10)

180

535,998

0.79 (0.67–0.94)

 

  ≥ 12 months

2906

1,390,661

0.97 (0.92–1.02)

1968

1,391,541

1.04 (0.97–1.11)

446

1,392,932

0.80 (0.70–0.92)

 
   

Ptrend, incl never = 0.70

  

Ptrend, incl never = 0.05(+)

  

Ptrend, incl never = 0.02

0.002

   

Ptrend, among ever = 0.10

  

Ptrend, among ever = 0.02(+)

  

Ptrend, among ever = 0.35

 
  1. aAdjusted for age, height (< 1.60, 1.60 to < 1.65, 1.65 to < 1.70, 1.70 to < 1.75, 1.75+ meters), BMI at age 18 (< 20, 20–21.9, 22–23.9, 24–26.9, 27+ kg/m2), weight change since age 18 (continuous, kg), age at menarche (< 12, 12, 13, 14, 15+ years), menopausal status (premenopausal, postmenopausal or unknown), age at natural menopause (continuous), HT use (never, past, current E only, current E + P, current other), alcohol consumption (non-drinker, < 5, 5–10, 10–15, 15+ g/day), total physical activity (< 3, 3–9, 9–18, 18–27, 27+ MET-h/day), family history of breast cancer (yes/no), history of benign breast disease (yes/no)
  2. bPhet for nulliparous and parous ever vs. never breastfed
  3. cPhet for nulliparous and number of children by ever vs. never breastfed
  4. dAmong parous women only, additionally adjusted for age at first birth (continuous, years), and parity and breastfeeding mutually adjusted
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Breast Cancer Research

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