Table 4. Association between menopausal hormone use categories and ovarian cancer risk by oral contraceptive use status, NIH-AARP Diet and Health Study Cohort, 1995–2006.

	Oral contraceptive use
	Never or <1 years			⩾1 years
	Number of cancers	Person-years	HRa (95% CI)	Number of cancers	Person-years	HRa (95% CI)	P -intx b
ET only among women with a hysterectomy at baseline (n=23 584)
No MHT use	17	39 722	1.00 (reference)	6	17 600	1.03 (0.54, 1.98)
ET only	54	65 118	1.97 (1.17, 3.30)	22	50 841	1.12 (0.60, 2.10)	0.15
Duration of ET only use (years)
<10	19	31 107	1.54 (0.81, 2.92)	8	27 145	0.80 (0.34, 1.89)	0.38
⩾10	35	32 886	2.52 (1.43, 4.43)	14	22 961	1.50 (0.74, 3.03)
EPT only among women with an intact uteri at baseline (n=68 596)
No MHT use	117	220 524	1.00 (reference)	32	95 645	0.83 (0.60, 1.14)
EPT only	55	81 534	1.46 (1.06, 2.01)	41	88 566	1.11 (0.76, 1.63)	0.75
Duration of EPT only use (years)
<10	37	60 414	1.30 (0.90, 1.90)	30	65 755	1.11 (0.73, 1.71)	0.65
⩾10	18	20 903	1.88 (1.17, 3.03)	11	22 670	1.09 (0.59, 2.04)
Regimen of EPT only use
Sequential	19	26 799	1.60 (0.99, 2.58)	16	29 744	1.29 (0.76, 2.22)	0.80
Continuous	29	38 970	1.55 (1.03, 2.34)	19	44 147	1.04 (0.63, 1.72)

Abbreviations: CI=confidence interval; EPT=oestrogen plus progestin therapy; ET=unopposed oestrogen therapy; HR, hazard ratio; MHT=menopausal hormone therapy; NIH-AARP=National Institutes of Health-AARP; RR=hazard rate ratio.

^aHR adjusted for continuous age (years), race (white, other/unknown), parity (nulliparous, 1, 2, 3+, unknown), and body mass index (<25, 25–29.9, ⩾30 kg m⁻², or unknown); models also contained terms for other formulations of menopausal hormone use and unknown use.

^bP-value (two-sided) from likelihood ratio test for the interaction of BMI and MHT formulations based on the categories and referent group shown.