Table 2.

Risk of breast cancer according to OC formulation in the Women’s CARE Study among women who reported exclusive use of a combination OC formulation that was used by at least 50 women^a

Variable	100 mcg mestranol/1.0 mg ethynodiol diacetate			35 mcg ethinyl estradiol/0.5 mg norethindrone			35 mcg ethinyl estradiol/1.0 mg norethindrone			50 mcg mestranol/1.0 mg norethindrone
	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)
	Total no. of subjects	1124	1085		1089	1034		1234	1172		1221	1206
General use
No useb	1032	980	1.0	1032	980	1.0	1032	980	1.0	1032	980	1.0
Ever use	81	95	0.8 (0.6–1.1)	47	44	1.2 (0.7–1.8)	192	179	1.0 (0.8–1.3)	179	213	0.8 (0.7–1.1)
Current usec							7	6	1.0 (0.3–3.0)
Former use	81	95	0.8 (0.6–1.1)	46	43	1.2 (0.7–1.8)	185	173	1.0 (0.8–1.3)	177	213	0.8 (0.6–1.1)
Duration of use
<2 years	19	23	0.8 (0.4–1.5)	28	26	1.2 (0.7–2.0)	70	68	0.9 (0.6–1.4)	50	65	0.8 (0.5–1.2)
2+ years	62	72	0.8 (0.5–1.1)	19	18	1.2 (0.6–2.3)	122	111	1.0 (0.8–1.4)	129	148	0.8 (0.6–1.1)
Time since last use
Current use							7	6	1.0 (0.3–3.0)
7 months–<5 years							13	11	1.1 (0.5–2.5)	8	7	1.2 (0.4–3.4)
5+ years	81	95	0.8 (0.6–1.1)	46	43	1.2 (0.7–1.8)	172	162	1.0 (0.8–1.3)	169	206	0.8 (0.6–1.0)

Variable	80 mcg mestranol/1.0 mg norethindrone			100 mcg mestranol/2.0 mg norethindrone			100 mcg mestranol/2.5 mg norethynodrel			30 mcg ethinyl estradiol/0.3 mg norgestrel
	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)
Total no. of subjects	1177	1168		1171	1137		1097	1047		1138	1081
General use
No useb	1032	980	1.0	1032	980	1.0	1032	980	1.0	1032	980	1.0
Ever use	132	178	0.7 (0.6–0.9)*	129	146	0.8 (0.6–1.1)	55	57	0.9 (0.6–1.3)	95	90	1.0 (0.7–1.4)
Current usec
Former use	131	178	0.7 (0.6–0.9)*	129	146	0.8 (0.6–1.1)	55	57	0.9 (0.6–1.3)	85	86	1.0 (0.7–1.3)
Duration of use
<2 years	40	60	0.6 (0.4–0.99)*	55	52	1.1 (0.7–1.6)	21	27	0.8 (0.4–1.4)	41	28	1.5 (0.9–2.6)
2+ years	92	118	0.8 (0.6–1.0)	74	94	0.7 (0.5–0.9)*	34	30	1.0 (0.6–1.7)	53	62	0.8 (0.5–1.1)
Time since last use
Current use
7 months–<5 years
5+ years	131	175	0.7 (0.6–0.96)*	129	145	0.8 (0.6–1.1)	55	57	0.9 (0.6–1.3)	83	82	1.0 (0.7–1.4)

Variable	50 mcg ethinyl estradiol/0.5 mg norgestrel			35 mcg ethinyl estradiol/0.5 mg (7 days), 0.75 mg (7 days), 1.0 mg (7 days) norethindrone
	Cases	Controls	OR (95% CI)	Cases	Controls	OR (95% CI)
Total no. of subjects	1112	1085		1062	1038
General use
No useb	1032	980	1.0	1032	980	1.0
Ever use	68	94	0.8 (0.5–1.1)	20	48	0.5 (0.3–0.8)*
Current usec
Former use	68	92	0.8 (0.5–1.1)	18	44	0.5 (0.3–0.8)*
Duration of use
<2 years	24	25	1.1 (0.6–2.0)	7	17	0.5 (0.2–1.4)
2+ years	44	69	0.6 (0.4–0.98)*	13	31	0.4 (0.2–0.8)*
Time since last use
Current use
7 months–<5 years
5+ years	67	91	0.8 (0.5–1.1)	18	38	0.5 (0.3–0.97)*

^*Denotes statistical significance at the .05 level; mcg denotes micrograms; mg denotes milligrams.

^aOdds ratios were derived by conditional logistic regression with the study site, race and age (in 5-year categories) as conditioning variables and were adjusted using categorical variables for menopausal status (pre- or perimenopausal, postmenopausal, unable to classify); age at menarche (<12 years, 12 years, >12 years); age at menopause among menopausal women (<45 years, 45–49 years, ≥50 years, unknown); number of term pregnancies (0, 1, 2, ≥3); age at first term pregnancy among parous women (<20 years, 20–24 years, ≥25 years); body mass index 5 years before reference date (<25, ≥25); family history of breast cancer in the woman’s mother, sister or daughter (no, yes, adopted or unknown); and ever use of hormone replacement therapy (no, yes). Women with missing values not included in one of the specified categories were excluded. Cell sizes, ORs and CIs were left blank when an OC exposure measure for a specific OC formulation had any cell size <5 due to imprecision or incalculability; no calculable OR that was omitted due to a cell size <5 was statistically significant.

^bThe reference group was the group of women who had never used OCs.

^cCurrent use was defined as use within 6 months before the reference date.