Table 2.

Relative risk (RR) of invasive endometrial cancer by status, dose and duration of aspirin use with prospective follow-up from 1980–2004 in the Nurses’ Health Study

Aspirin use	# cases	Total person- years	Age-adjusted RR (95% CI)
Status of aspirin use
Never‡	123	321,114	1.0
Past	235	326,209	1.22 (0.98–1.52)
Current§	389	717,821	1.07 (0.87–1.32)
Current, 1–2 tablets/week	163	328,944	1.03 (0.81–1.31)
Current, 3–5 tablets/week	74	145,544	1.01 (0.75–1.35)
Current, 6+ tablets/week	136	204,947	1.23 (0.96–1.57)
Duration of aspirin use**(Current users only)
Never‡	123	321,114	1.0
<2 years	132	247,433	1.06 (0.82–1.36)
2–10 years	72	122,083	1.04 (0.77–1.40)
> 10 years	119	230,099	1.06 (0.82–1.37)
P for trend			0.92
Dosage of aspirin use (cumulative average # tablets/week among current and past users)
Never‡	123	321,114	1.0
>0 to <2 tablets/week	283	488,589	1.11 (0.89–1.37)
2–7 tablets/week	218	355,837	1.07 (0.85–1.34)
>7 tablets/week	104	157,764	1.30 (1.00–1.70)
P for trend			0.09

^†Multivariate risks from proportional hazards models are adjusted for BMI (<20 [ref], 20 to <21, 21 to <22, 22 to <23, 23 to <24, 24 to <25, 25 to <27, 27 to <29, 29 to <30, 30 to <32, 32 to <35, 35 to < 40, ≥ 40), duration of oral contraceptive use (never [ref], past use <3 years, past 3–5 years, past >5 years), pack years of smoking (never, >0 to 20 years, >20 to 40 years, >40 years), use and duration of postmenopausal hormones (never/premenopausal [ref], past use less than 5 years, past use greater than 5 years, current use less than 5 years, current use greater than 5 years), age at menopause (premenopausal [ref], postmenopausal <45 years, 45–49 years, 50–52 years, > 53 years), parity (1–2 [ref], 3–4, ≥ 5), age at menarche (<12, 12 [ref], >12), hypertension (present, absent), diabetes (present, absent);

^‡referent group never is no reported use during the follow up period;

^§Includes current users with unknown quantity;

^**cumulative average # of years among current users