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Table 4 Risk ratios of contralateral breast cancer associated with tamoxifen use by patient and tumor characteristics

From: Systemic therapy for breast cancer and risk of subsequent contralateral breast cancer in the WECARE Study

  No tamoxifen Tamoxifen  
CBC cases UBC controls RR CBC cases UBC controls RRa (95 % CI) P het.
N (%) N (%)   N (%) N (%)
Age at 1st breast cancer (years)b        
 ≤39 222 (83) 293 (76) 1.0 46 (17) 91 (24) 0.69 (0.43–1.10)  
 40–49 559 (69) 782 (66) 1.0 249 (31) 398 (34) 0.79 (0.62–1.01) 0.9
 50–54 273 (61) 350 (54) 1.0 172 (39) 298 (46) 0.75 (0.56–1.00)  
Year of diagnosis of first breast cancer        
 1985–1989 250 (83) 472 (81) 1.0 53 (17) 108 (19) 1.18 (0.75–1.87)  
 1990–1994 400 (70) 564 (65) 1.0 172 (30) 307 (35) 0.86 (0.65–1.13)  
 1995–1999 280 (66) 306 (56) 1.0 146 (34) 245 (44) 0.65 (0.48–0.88) 0.1
 2000–2004 101 (54) 71 (37) 1.0 85 (46) 119 (63) 0.52 (0.32–0.85)  
 2005–2008 23 (68) 12 (60) 1.0 11 (32) 8 (40) 0.88 (0.26–2.92)  
First-degree family history of breast cancerc        
 Yes 344 (69) 298 (63) 1.0 154 (31) 172 (37) 0.82 (0.60–1-12)  
 No 703 (70) 1115 (65) 1.0 307 (30) 602 (35) 0.76 (0.62–0.94) 0.7
 Unknownd 7 (54) 12 (48) 1.0 6 (46) 13 (52)   
BMI at 1st breast cancer (kg/m2)        
 <25 749 (71) 991 (66) 1.0 303 (29) 506 (34) 0.76 (0.61–0.95)  
 25–29.9 191 (64) 307 (62) 1.0 108 (36) 189 (38) 0.81 (0.57–1.15) 0.9
 ≥30 111 (67) 124 (58) 1.0 55 (33) 91 (42) 0.71 (0.44–1.14)  
 Unknownd 3 (75) 3 (75) 1.0 1 (25) 1 (25)   
Histology of first breast cancere        
 Lobular 112 (63) 103 (46) 1.0 67 (37) 120 (54) 0.48 (0.31–0.75) 0.03
 Other 940 (70) 1,321 (67) 1.0 398 (30) 665 (33) 0.82 (0.67–0.99)  
 Unknownd 2 (50) 1 (33)   2 (50) 2 (67)   
ER/PR status of first breast cancerf        
 Positive 450 (52) 679 (49) 1.0 413 (48) 700 (51) 0.75 (0.60–0.93)  
 Negative 388 (94) 422 (89) 1.0 25 (6) 51 (11) 0.54 (0.30–0.98) 0.3
 Unknownd 216 (88) 324 (90) 1.0 29 (12) 36 (10)   
  1. aAdjusted for age at first breast cancer diagnosis (continuous), first-degree family history of breast cancer (yes, no, unknown), histology (lobular, other, unknown), stage (local, regional, unknown) and ER/PR status (positive for either, negative, unknown) at first diagnosis, radiation (yes, no), chemotherapy (yes, no), and other endocrine therapy (yes, no)
  2. bRR are adjusted for all variables listed in footnote “a”, except age at first breast cancer diagnosis
  3. cRR are adjusted for all variables listed in footnote “a”, except first-degree family history of breast cancer
  4. dUnknown not included in model
  5. eRR are adjusted for all variables listed in footnote “a”, except histology of first breast cancer diagnosis
  6. fRR are adjusted for all variables listed in footnote “a”, except ER/PR status of first breast cancer diagnosis
  7. BMI body mass index, CBC contralateral breast cancer, CI confidence interval, ER/PR estrogen receptor/progesterone receptor, P het; P value for heterogeneity, RR risk ratio, UBC unilateral breast cancer