Table 2 Risk ratios of contralateral breast cancer associated with different aspects of tamoxifen use

Tamoxifen use

 Never

1054 (69)

1425 (64)

1.0 (Referent)

 Ever

467 (31)

787 (36)

0.76 (0.63–0.92)

Tamoxifen use according to time since first breast cancer

 1–4 years

  Never

423 (72)

644 (65)

1.0 (Referent)

  Ever

163 (28)

342 (35)

0.67 (0.51–0.88)

 5–9 years

  Never

387 (67)

504 (63)

1.0 (Referent)

  Ever

187 (33)

300 (37)

0.76 (0.57–1.03)

0.3

 ≥10 years

  Never

244 (68)

277 (66)

1.0 (Referent)

  Ever

117 (32)

145 (34)

0.95 (0.67–1.34)

Mean duration of tamoxifen (months)

40.2

40.5

0.8

Median duration of tamoxifen (months)

44

43

0.6

 Interquartile range (months)

20–60

18–60

 Range (months)

>0–106

>0–174

Duration of tamoxifen use

 Never

1054 (69)

1425 (64)

1.0 (Referent)

 ≤18 months

92 (6)

165 (7)

0.90 (0.65–1.24)

 19–53 months

139 (9)

242 (11)

0.76 (0.57–1.00)

0.7^e

 ≥54 months

167 (11)

244 (11)

0.80 (0.61–1.04)

 Unknown^b

69 (5)

136 (6)

Mean time since last use at reference date for past users (months)

57.1

45.2

0.0001

Median time since last use at reference date for past users (months)

48

37

0.0001

 Interquartile range (months)

24–83

13–65

 Range (months)

1–204

1–186

Time since last tamoxifen use at reference date^c

 Never

1054 (69)

1425 (64)

1.0 (Referent)

 Current use, 0 months since last use^d

131 (9)

249 (11)

0.73 (0.55–0.97)

 Past use, <37 months since last use

110 (7)

206 (9)

0.73 (0.53–1.00)

0.2^e

 Past use, ≥37 months since last use

161 (11)

208 (9)

0.98 (0.73–1.31)

 Unknown^b

65 (4)

124 (6)

Time since last tamoxifen use at reference date according to duration of use

 Never

1054 (69)

1425 (64)

1.0 (Referent)

 <54 months duration

  Current use^d

101 (7)

178 (8)

0.86 (0.62–1.19)

  Past use, <37 months since last use

53 (3)

112 (5)

0.71 (0.47–1.07)

  Past use, ≥37 months since last use

77 (5)

117 (5)

0.82 (0.56–1.19)

 ≥54 months duration

0.01^e

  Current use^d

28 (2)

69 (3)

0.44 (0.27–0.73)

  Past use, <37 months since last use

56 (4)

90 (4)

0.71 (0.45–1.12)

  Past use, ≥37 months since last use

83 (5)

85 (4)

1.25 (0.84–1.86)

  Unknown duration^b

69 (5)

136 (6)