Table 3.

Use of medications for type 2 diabetes in relation to ER+ and ER− breast cancer incidence

	ER+ breast cancer		ER− breast cancer
	Cases	MV HR (95% CI)	Cases	MV HR (95% CI)
No diabetes	841	Reference	426	Reference
T2D medication use*
No	13	0.93 (0.54, 1.61)	12	2.03 (1.13–3.62)
Yes	58	1.07 (0.81, 1.40)	29	1.30 (0.88–1.92)
Type of medication*
Metformin	37	0.92 (0.65–1.28)	21	1.26 (0.80–1.98)
All other types	21	1.49 (0.96–2.32)	8	1.41 (0.69–2.86)

^*Medications reported in the three most recent follow-up questionnaires, covering period of approximately 6 years prior to breast cancer diagnosis (for cases) or end of follow-up (non-cases)

HRs adjusted for age, BMI, BMI at age 18, parity, age at first birth, age at menarche, duration of oral contraceptive use, duration of menopausal hormone use, and first degree family history of breast cancer.