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Table 5 Risk ratios of contralateral breast cancer associated with chemotherapy by time, patient, and tumor characteristics

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

  No chemotherapy Chemotherapy  
CBC cases UBC controls RR CBC cases UBC controls RRa (95 % CI) P het.
N (%) N (%)   N (%) N (%)
Ever use of chemotherapy (yes/no) 699 (46) 923 (42) 1.0 822 (54) 1,289 (58) 0.71 (0.59–0.85)  
Time since first breast cancer (years)        
 1–4 278 (47) 402 (41) 1.0 308 (53) 584 (59) 0.59 (0.45–0.77)  
 5–9 249 (43) 322 (40) 1.0 325 (57) 482 (60) 0.73 (0.56–0.95) 0.1
 ≥10 172 (48) 199 (47) 1.0 189 (52) 223 (53) 0.92 (0.65–1.30)  
Age at 1st breast cancer (years)b        
 ≤39 59 (22) 88 (23) 1.0 209 (78) 296 (77) 0.99 (0.63–1.57)  
 40–49 372 (46) 469 (40) 1.0 436 (54) 711 (60) 0.65 (0.52–0.82) 0.2
 50–54 268 (60) 366 (56) 1.0 177 (40) 282 (44) 0.70 (0.52–0.94)  
Year of diagnosis of first breast cancer        
 1985–1989 192 (63) 295 (51) 1.0 111 (37) 285 (49) 0.66 (0.46–0.95)  
 1990–1994 283 (49) 392 (45) 1.0 289 (51) 479 (55) 0.71 (0.55–0.92)  
 1995–1999 157 (37) 190 (34) 1.0 269 (63) 361 (66) 0.79 (0.58–1.08) 0.5
 2000–2004 58 (31) 40 (21) 1.0 128 (69) 150 (79) 0.47 (0.27–0.83)  
 2005–2008 9 (26) 6 (30) 1.0 25 (74) 14 (70) 1.17 (0.31–4.43)  
First-degree family history of breast cancerc        
 Yes 219 (44) 211 (45) 1.0 279 (56) 259 (55) 0.89 (0.65–1.20)  
 No 474 (47) 704 (41) 1.0 536 (53) 1,013 (59) 0.65 (0.53–0.80) 0.07
 Unknownd 6 (46) 8 (32) 1.0 7 (54) 17 (68)   
BMI at first breast cancer (kg/m2)        
 <25 538 (51) 660 (44) 1.0 514 (49) 837 (56) 0.66 (0.53-0.81)  
 25–29.9 107 (36) 192 (39) 1.0 192 (64) 304 (61) 0.83 (0.59-1.18) 0.3
 ≥30 52 (31) 68 (32) 1.0 114 (69) 147 (68) 0.89 (0.55-1.44)  
 Unknownd 2 (50) 3 (75) 1.0 2 (50) 1 (25)   
Histology of first breast cancere        
 Lobular 86 (48) 94 (42) 1.0 93 (52) 129 (58) 0.77 (0.49–1.21)  
 Other 610 (46) 828 (42) 1.0 728 (54) 1,158 (58) 0.70 (0.58–0.85) 0.7
 Unknownd 3 (75) 1 (33)   1 (25) 2 (67)   
ER/PR status of first breast cancerf        
 Positive 419 (49) 609 (44) 1.0 444 (51) 770 (56) 0.72 (0.57–0.91)  
 Negative 91 (22) 96 (20) 1.0 322 (78) 377 (80) 0.67 (0.45–1.02) 0.8
 Unknownd 189 (77) 218 (61) 1.0 56 (23) 142 (39)   
  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 breast cancer diagnosis, radiation therapy (yes, no), and 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