Table 7.
Risk ratios of contralateral breast cancer associated with different combinations of breast cancer treatment
| 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) | ||
aAll treatment categories include surgery
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
cIncludes aromatase inhibitors (67 cases and 99 controls) and other anti-estrogens
d P value overall = 0.002 if the category “Radiotherapy alone” is removed from the model
CBC contralateral breast cancer, CI confidence interval, RR risk ratio, UBC unilateral breast cancer