Table 5.

Effect of lifetime chest X-ray exposure (any exposure) on breast cancer risk according to the number of exposures, the age at first exposure, and the first full-term pregnancy by birth cohort

	Number of				Number of				Number of				Pb
	Cases	Ctrls	ORa	95% CI	Cases	Ctrls	ORa	95% CI	Cases	Ctrls	ORa	95% CI
	Birth cohort
	≤ 1945				1946–1959				≥ 1960
Chest X-ray exposure
No	47	31	1		96	92	1		65	116	1
Yes	431	259	1.57	0.72-3.43	678	605	1.65	1.06–2.56	195	240	2.54	1.63–3.98	0.024
Number of exposures
0	47	31	1		96	92	1		65	116	1
1–3	134	81	1.72	0.74–3.98	179	197	1.24	0.75–2.05	79	112	2.04	1.22–3.40
4–9	81	46	2.04	0.82–5.07	122	111	1.70	0.98–2.94	48	43	3.77	2.03–7.01	0.041
≥10	105	64	1.44	0.60–3.45	142	130	2.26	1.31–3.90	16	21	2.77	1.19–6.47
Continuous			1.01	0.99–1.03			1.04	1.02–1.06			1.06	1.01–1.12	0.013
Age at first exposure, yearsc
No exposure	47	31	0.52	0.23–1.21	96	92	0.77	0.47–1.25	65	116	0.47	0.28–0.78
≥20	163	119	1		237	261	1		85	110	1
15–19	87	45	0.74	0.38–1.42	159	123	1.07	0.69–1.66	42	54	1.13	0.64–2.00	0.67
<15	122	64	0.83	0.47–1.46	140	114	1.40	0.89–2.18	28	41	0.91	0.47–1.79
Continuous			1.01	0.99–1.02			1.00	0.98–1.01			1.02	0.99–1.05	0.49
According to first full-term pregnancy (FFTP)c
Only after FFTPd	109	59	1		124	139	1		35	34	1
Before (incl. no FTP)	268	175	0.48	0.27–0.86	429	373	0.95	0.63–1.44	128	177	0.86	0.45–1.63	0.19

Abbreviations: OR (95% CI) odds ratio (95% confidence interval

^aAdjusted for age at censoring (when by birth cohort analysis) and for birth cohort (continuous) (when by age at censure analysis), number of full-term pregnancies (>2; 1–2; 0), mammography use (never; ever), educational level (intermediate/high; basic; not graduated), BMI (18.5–24.99; <18.5; ≥25 and <30; ≥30), smoking (no; current; past), and family history of breast cancer (0;1st degree; 2nd degree)

^bP value for heterogeneity test

^cAdjusted as in ^a plus number of exposures (≤5; >5)

^dAfter = also includes chest X-ray exposure that occurred during year of first full-term pregnancy