Table 3.

Relation of age at menarche to tumor-defined characteristics of breast cancer

	Age at menarche, years
	Odds ratio (95% confidence interval)a, b
Tumor characteristic	≤11	> 11 and ≤13	> 13 and ≤14
Tumor size
1–10 mm
11–20 mm	1.00 (0.65–1.53)	0.96 (0.74–1.25)	1.01 (0.76–1.33)
≥21 mm	1.05 (0.64–1.72)	1.43 (1.06–1.92)	1.32 (0.96–1.81)
Grade
Low
Medium	2.05 (1.00–4.19)	1.47 (1.00–2.15)	1.74 (1.15–2.62)
High	2.04 (1.01–4.16)	1.55 (1.06–2.26)	1.45 (1.00–2.19)
ER status
Positive
Negative	1.33 (0.82–2.16)	0.94 (0.68–1.29)	1.15 (0.83–1.61)
PR status
Positive
Negative	0.86 (0.54–1.36)	0.99 (0.75–1.30)	1.24 (0.93–1.66)
Lymph node involvement
Absent
Present	1.49 (1.02–2.19)	1.29 (1.02–1.65)	1.22 (0.95–1.58)
Histology
Ductal
Lobular	1.17 (0.68–2.01)	1.08 (0.76–1.52)	0.99 (0.68–1.43)
All other	0.68 (0.39–1.18)	1.09 (0.81–1.46)	0.92 (0.66–1.26)

^aReference group: age at menarche of more than 14 years, with the category of best prognosis within each tumor characteristic. ^bOdds ratio estimates adjusted for body mass index at 18 years of age, age at first birth, age at diagnosis, and ever use and type of menopausal hormone therapy (never users, exclusive estrogen therapy, and combined estrogen-progestin therapy). ER, estrogen receptor; PR, progesterone receptor.