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Table 7 Risk ratios of contralateral breast cancer associated with different combinations of breast cancer treatment

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

Treatment for first breast cancera CBC cases UBC controls  
N (%) N (%) RRb (95 % CI) Overall P valued
Surgery alone 249 (16) 156 (7) 1.00 (Referent)  
Chemotherapy alone 209 (14) 197 (9) 0.68 (0.49–0.93)  
Tamoxifen alone 81 (5) 58 (3) 1.06 (0.69–1.64)  
Radiotherapy alone 244 (16) 470 (21) 1.13 (0.88–1.47) <0.0001
Chemotherapy + tamoxifen 81 (5) 83 (4) 0.70 (0.47–1.05)  
Chemotherapy + radiotherapy 319 (21) 569 (26) 0.82 (0.62–1.09)  
Tamoxifen + radiotherapy 107 (7) 208 (9) 0.83 (0.60–1.16)  
Chemotherapy + tamoxifen + radiotherapy 142 (9) 329 (15) 0.54 (0.39–0.76)  
Other endocrine therapyc ± other treatment 89 (6) 141 (6) 0.49 (0.33–0.72)  
One treatment or more unknown 0 (0) 1 (0.05)   
  1. aAll treatment categories include surgery
  2. bAdjusted for all variables in the Table plus 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 estrogen receptor/progesterone receptor status (positive for either, negative, unknown) at first breast cancer diagnosis
  3. cIncludes aromatase inhibitors (67 cases and 99 controls) and other anti-estrogens
  4. d P value overall  = 0.002 if the category “Radiotherapy alone” is removed from the model
  5. CBC contralateral breast cancer, CI confidence interval, RR risk ratio, UBC unilateral breast cancer