Table 4.

Breast cancer-specific five-year survival in relation to menstrual factors

Menstrual factors	Deaths	Mortality ratea	Hazard ratio (95% CI)b
Age at menarch, yearsc
> 14	46	1.81	1.00 (reference)
> 13 and ≤14	71	2.19	1.26 (0.86–1.84)
> 11 and ≤13	89	1.93	1.14 (0.79–1.65)
≤11	23	2.99	1.72 (1.02–2.89)
Irregular menstruation
No	253	2.16	1.00 (reference)
Yes	7	1.77	0.91 (0.43–1.93)
Cycle length, days
≤27.5	39	1.79	1.00 (reference)
28	95	2.16	1.15 (0.78–1.68)
> 28	29	1.78	0.98 (0.60–1.61)
Total lifetime menstrual cycles, number
≤423	58	2.10	1.00 (reference)
> 423 and ≤500	104	2.00	0.99 (0.71–1.38)
> 500	57	2.09	1.04 (0.72–1.52)
Age at menopause, years
< 50	79	2.43	1.00 (reference)
50–55	138	2.18	0.92 (0.69–1.22)
> 55	17	2.22	1.04 (0.60–1.80)

^aBreast cancer deaths per 100 person-years. ^bAll menstrual factor hazard ratio estimates adjusted for age at first birth, age at diagnosis, ever use and type of menopausal hormone therapy (never users, exclusive estrogen therapy, and combined estrogen-progestin therapy).^cAge at menarche hazard ratio estimates additionally adjusted for body mass index at 18 years of age.