Table 4. Risks of breast cancer after supradiaphragmatic radiotherapy in relation to age at menopause.

Risk factor	Cases	Controls	Total	ORa (95% CI)	P-value
Menopause before age 40
No	103	598	701	1.00
Yes	49	454	503	0.65 (0.44–0.94)	0.02
Unknown	32	168	200	1.09 (0.69–1.73)	0.70
Menopause within 5 years of start of treatment
No	205	1399	1604	1.00
Yes	26	357	383	0.55 (0.35–0.85)	0.01
Unknown	34	337	371	0.92 (0.61–1.38)	0.68
Premenopausal years after start of treatment
Less than 1	10	103	113	1.00
1–4	7	98	105	0.96 (0.34–2.69)	0.94
5–9	7	84	91	1.02 (0.36–2.87)	0.97
10–14	19	277	296	1.49 (0.63–3.55)	0.36
15–24	49	281	330	1.62 (0.76–3.44)	0.21
25 or over	25	40	65	3.56 (1.50–8.45)	0.004
Unknown	52	294	346	1.74 (0.84–3.64)	0.14
				Ptrend=0.003

Abbreviations: CI=confidence interval; OR=odds ratio; sRT=supradiaphragmatic radiotherapy.

^aOdds ratios are adjusted for age and year of treatment, duration between treatment and questionnaire completion, calendar year of birth, sRT field.