Table 4.

Bilateral oophorectomy and risk of breast cancer, stratified by BRCA mutation status and by age at diagnosis

Variable	Age-adjusted HR (95% CI)	P	Multivariable*HR (95% CI)	P
All women
BRCA1† mutation carriers
Oophorectomy‡
No	1.00 (Referent)		1.00 (Referent)
Yes	0.96 (0.73 to 1.26)	.76	0.97 (0.73 to 1.29)	.85
BRCA2† mutation carriers
Oophorectomy‡
No	1.00 (Referent)		1.00 (Referent)
Yes	0.65 (0.37 to 1.16)	.14	0.68 (0.38 to 1.21)	.19
Breast cancer diagnosed prior to age 50 y§
BRCA1† mutation carriers
Oophorectomy‡
No	1.00 (Referent)		1.00 (Referent)
Yes	0.79 (0.55 to 1.13)	.51	0.84 (0.58 to 1.21)	.34
BRCA2† mutation carriers
Oophorectomy‡
No	1.00 (Referent)		1.00 (Referent)
Yes	0.18 (0.05 to 0.63)	.007	0.17 (0.05 to 0.61)	.006

^*Adjusted for age at baseline (continuous), family history of breast cancer (0, 1, 2, ≥3 affected first-degree relatives), country of residence (Poland, Canada, United States, other) oral contraceptive use (ever/never), age at menarche (≤12, 13, ≥14 years), parity (0, 1, 2, 3, ≥4 children), and breastfeeding (ever/never). CI = confidence interval; HR = hazard ratio.

†Women with both a BRCA1 and BRCA2 mutation were coded as missing.

‡Oophorectomy was coded as a time-dependent covariate. Oophorectomy refers to bilateral oophorectomies only. Others variables were dichotomized based on exposure at baseline.

§Follow-up was censored at age 50 years; thus, women older than age 50 years at baseline were excluded from this analysis.