Table 3 Risk ratios of ER-positive and ER-negative contralateral breast cancer associated with different aspects of tamoxifen use

ER-positive CBC^b

  Never

525 (63)

692 (62)

1.0 (referent)

  Ever

303 (37)

421 (38)

0.75 (0.58–0.96)

 Duration of tamoxifen use

  Never

525 (63)

692 (62)

1.0 (referent)

  <54 months

142 (17)

198 (18)

0.84 (0.61–1.15)

  ≥54 months

117 (14)

149 (13)

0.80 (0.57–1.12)

  Unknown^c

44 (5)

74 (7)

  Test for trend

0.2

  Overall P value

0.3

 Time since last use at reference date

  Never

525 (63)

692 (62)

1.0 (referent)

  Current use, duration <54 months

56 (7)

83 (7)

0.82 (0.52–1.30)

  Current use, duration ≥54 months

20 (2)

41 (4)

0.38 (0.20–0.72)

  Past use, <37 months since last use

68 (8)

97 (9)

0.72 (0.47–1.12)

  Past use, ≥37 months since last use

116 (14)

131 (12)

1.07 (0.74–1.56)

  Unknown^c

43 (5)

69 (6)

  Overall P value

0.02

ER-negative CBC^b

  Never

282 (78)

318 (64)

1.0 (referent)

  Ever

79 (22)

180 (36)

0.92 (0.59–1.44)

 Duration of tamoxifen use

  Never

282 (78)

318 (64)

1.0 (referent)

  <54 months

39 (11)

87 (17)

1.03 (0.58–1.82)

  ≥54 months

29 (8)

58 (12)

0.93 (0.50–1.74)

  Unknown^c

11 (3)

35 (7)

  Test for trend

0.9

  Overall P value

1.0

 Time since last use at reference date

  Never

282 (78)

318 (64)

1.0 (referent)

  Current use, duration <54 months

18 (5)

35 (7)

1.54 (0.68–3.47)

  Current use, duration ≥54 months

5 (1)

14 (3)

0.76 (0.25–2.37)

  Past use, <37 months since last use

21 (6)

45 (9)

1.12 (0.55–2.27)

  Past use, ≥37 months since last use

25 (7)

55 (11)

0.66 (0.31–1.42)

  Unknown^c

10 (3)

31 (6)

  Overall P value

0.6