Table 1.

Characteristics of ovarian cancer cases and controls in the NECC and the NHS

Characteristic	NECC					NHS*
Characteristic		Cases	Controls	P^†	Cases	Controls	P^†
N	1,175	1,202		210	600
Mean (SD)
Age (y)^‡	51 (13)	51 (13)	0.37	62 (8)	62 (8)	0.93
Parity among parous women	2.5 (1.3)	2.8 (1.5)	<0.001	3.0 (1.3)	3.4 (1.5)	0.004
Duration oral contraceptive use (mo)^§	52 (54)	61 (55)	0.006	46 (42)	53 (49)	0.22
BMI (kg/m²)	26.3 (6.3)	25.7 (5.5)	0.02	25.7 (5.0)	25.7 (4.5)	0.94
Duration PMH use (mo)^§	78 (86)	74 (71)	0.64	96 (84)	85 (68)	0.18
Duration of lactation (mo)^∥	5.0 (10.0)	7.3 (13.2)	<0.001	6.0 (10.3)	7.2 (9.7)	0.17
Percent of study population
Parous	68	81	<0.001	89	93	0.05
Ever user of oral contraceptives	48	60	<0.001	42	45	0.57
History of tubal ligation	14	18	0.007	14	21	0.02
Ever user of PMH	17	20	0.14	71	63	0.02
Family history of ovarian cancer	5.1	2.8	0.004	9.1	3.7	0.002
Any history of genital talc use	29	24	0.003	40	39	0.79
Regular genital talc use (once a week or more)	27	20	<0.001	29	24	0.15
Daily genital talc use	16	12	0.006	18	13	0.08
Genotype frequencies, %
GSTM1 null	51	53	0.42	48	52	0.36
GSTT1 null	21	22	0.85	19	21	0.45
NAT2 slow acetylator^¶	63	64	0.74	59	67	0.05

↵* In the NHS, duration of lactation was collected in 1986, family history of ovarian cancer was first collected in 1992, and history of genital talc use was collected in 1982; for variables collected on multiple questionnaires, the value from two cycles (2-4 y) before the date of diagnosis for each case was used for the case and their matched controls.
↵† P values calculated using proc t test (continuous variables) or a χ² test (binary variables).
↵‡ Cases and controls in each study population were matched (NHS) or frequency-matched (NECC) on age.
↵§ Duration of oral contraceptive use and PMH use among ever users.
↵∥ Total duration among parous women.
↵¶ NAT2 acetylation genotype based on analysis of three single nucleotide polymorphisms, I114T, R197Q, and G286E.