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Table 1 Baseline characteristics of participants based on birth cohort group

From: Differential patterns of reproductive and lifestyle risk factors for breast cancer according to birth cohorts among women in China, Japan and Korea

 

Total N (%)

 ≤ 1920s N (%)

1930s N (%)

1940s N (%)

 ≥ 1950s N (%)

P value

 

311,955

71,689 (23.0)

92,643 (29.7)

80,775 (25.9)

66,848 (21.4)

 

Breast cancer cases

4581 (1.5)

707 (1.0)

1279 (1.4)

1385 (1.8)

1210 (1.8)

 < 0.001

Baseline year (min–max)

1993–2015

1993–2007

1993–2013

1993–2014

1993–2015

 < 0.001

Follow-up duration (years, mean ± SD)

16.5 ± 6.6

15.4 ± 8.4

17.1 ± 6.4

17.8 ± 5.8

15.4 ± 4.9

 < 0.001

Follow-up duration among breast cancer cases (years, mean ± SD)

10.2 ± 6.6

11.7 ± 8.5

10.4 ± 6.6

10.4 ± 6.3

8.9 ± 5.3

 < 0.001

Age at baseline (years, mean)

54.2 ± 10.7

65.3 ± 9.3

57.7 ± 7.2

48.8 ± 7.0

4401 ± 5.3

 < 0.001

Age at baseline among breast cancer cases (years, mean)

51.7 ± 9.3

60.9 ± 9.8

57.3 ± 7.6

48.8 ± 6.3

44.0 ± 3.8

 < 0.001

Age at diagnosis of breast cancer cases (years, mean)

61.9 ± 10.4

72.6 ± 9.1

67.6 ± 8.3

59.2 ± 7.6

52.8 ± 6.0

 < 0.001

Menopausal status

     

 < 0.001

Premenopausal

103,195 (33.1)

4206 (5.9)

7960 (8.6)

40,040 (49.6)

50,989 (76.3)

 

Postmenopausal

194,390 (62.3)

66,276 (92.5)

81,975 (88.5)

35,031 (43.4)

11,108 (16.6)

 

 Unknown

14,370 (4.6)

1207 (1.7)

2708 (1.68)

5704 (7.6)

4751 (7.1)

 

Age at menarche

     

 < 0.001

  < 13 years

19,766 (6.3)

2074 (2.9)

3451 (3.7)

7777 (9.6)

6464 (9.7)

 

 13–14 years

102,516 (32.9)

16,314 (22.8)

25,509 (27,5)

34,057 (42.2)

26,636 (39,9)

 

 15–16 years

107,179 (34.4)

26,198 (36.5)

34,547 (37.3)

24,411 (30.2)

22,023 (32.9)

 

 17 + years

55,673 (17.8)

16,306 (22.8)

21,726 (23.5)

9641 (11.9)

8000 (12.0)

 

 Missing

26,821 (8.6)

10,797 (15,1)

7410 (8,0)

4889 (6,1)

3725 (8.6)

 

Age at menopausea

     

 < 0.001

  < 45 years

28,040 (14.4)

7633 (11.5)

10,080 (12.3)

6745 (19.3)

3582 (32.3)

 

 45–49 years

61,684 (31.7)

17,886 (27.0)

26,928 (32.9)

13,631 (38.9)

3239 (29.2)

 

 50–54 years

74,612 (38.4)

25,241 (38.1)

34,748 (42.4)

11,581 (33.1)

3042 (27.4)

 

 55 + years

8711 (4.5)

3588 (5.4)

3680 (4.5)

1112 (3.2)

331 (3.0)

 

 Missing

21,343 (11.0)

11,928 (18.0)

6539 (8.0)

1962 (5.6)

914 (8.2)

 

Parity

     

 < 0.001

 Nulliparous

290,865 (93.2)

63,542 (88.6)

87,281 (94,2)

76,141 (94.3)

63,910 (96.6)

 

 Parous

21,090 (6.8)

8147 (11.4)

5362 (5.8)

4634 (5.7)

2947 (4.4)

 

Number of children

     

 < 0.001

 0

12,601 (4.0)

3201 (4.5)

3460 (3.7)

2993 (3.7)

2947 (4.4)

 

 1–2

148,522 [47, 61]

13,915 (19.4)

36,444 (39.3)

44,686 (55.3)

53,477 (80.0)

 

 3–4

93,958 [30, 1]

23,267(32.5)

36,507 (39.4)

24,684 (30.6)

9500 (14.2)

 

 5 + 

26,601 (8.5)

12,180 (17.0)

9934 (10.7)

3830 (4.7)

657 (1.0)

 

 Missing

30,273 (9.7)

19,126 (26,7)

6298 (6.8)

4582 (5.7)

267 (0.4)

 

Age at first delivery (%)

     

 < 0.001

  ≤ 20 years

28,979 (9.3)

9027 (12.6)

12,580 (13.6)

5582 (6.9)

1790 (2.7)

 

 21–25 years

146,015 (46.8)

35,408 (49.4)

47,325 (51.1)

42,575 (52.7)

20,707 (31.0)

 

 26–30 years

90,182 (28.9)

13,411 (18.7)

21,087 (22.8)

22,275 (27.6)

33,409 (49.98)

 

  > 30 years

18,275 (5.9)

3000 (4.2)

3955 (4.3)

4227 (5.2)

7093 (10.6)

 

 Nulliparous

21,090 (6.8)

8147 (11.4)

5362 (5.7)

2947 (4.4)

21,090 (6.8)

 

Breastfeeding among parous

     

 < 0.001

 Yes

103,181 (35.5)

14,744 (23.2)

36,073 (41.3)

30,419 (40.0)

21,945 (34.3)

 

 No

15,828 (5.4)

860 (1.4)

4084 (4.7)

6403 (8.4)

4481 (7.0)

 

 Missing

171,856 (59.1)

47,938 (75.4)

47,124 (54.0)

39,319 (51,6)

37,475 (58.7)

 

Smoking status

     

 < 0.001

 Never

264,230 (84.7)

53,881 (75.2)

77,561 (83.7)

70,847 (87.7)

61,941 (92.7)

 

 Ever

23,058 (7.4)

6842 (9.5)

6555 (7.1)

5945 (7.4)

3716 (5.6)

 

 Missing

24,667 (7.9)

10,966 (15.3)

8527 (9.2)

3983 (4.9)

1191 (1.8)

 

Alcohol drinking

     

 < 0.001

 Non-drinkerb

208,535 (66.9)

48,200 (67.2)

60,066 (64.8)

50,061 (62.0)

50,208 (75.1)

 

 Current drinker

53,682 (17.2)

11,320 (15.8)

14,304 (15.4)

16,074 (19.9)

11,984 (17.9)

 

 Missing

49,738 (15.9)

12,169 (17.0)

18,273 (19.7)

14,640 (18,1)

4656 (7.0)

 
  1. aThe result regarding menopause age was based on the analysis of post-menopausal women
  2. bThe non-drinker category of alcohol consumption included both participants who never drank alcohol and ex-drinkers
  3. P value comparisons across class categories are based on the chi-square test for categorical variables; P values for continuous variables are based on ANOVA
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Breast Cancer Research

ISSN: 1465-542X

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