Table 8.

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 estrogen receptor tumor status

	Estrogen receptor (ER) tumor status
	ER negative				ER positive				Unknown
	Controls	Cases	ORa	95% CI	Cases	ORa	95% CI	Pb	Cases	ORa	95% CI
Chest X-ray exposure
No	239	32	1		107	1			69	1
Yes	1104	132	1.50	0.94–2.39	692	2.13	1.56–2.91	0.16	480	2.21	1.51–3.24
Number of exposures
0	239	32	1		107	1			69	1
1–3	390	43	1.31	0.77–2.25	207	1.73	1.22–2.46	0.67	142	1.87	1.21–2.87
4–9	200	29	1.99	1.10–3.62	140	2.65	1.80–3.92		82	2.51	1.55–4.07
≥10	215	21	1.51	0.79–2.90	124	2.23	1.49–3.33		118	3.27	2.03–5.28
Continuous			1.01	0.99–1.04		1.02	1.00–1.03	0.58		1.03	1.01–1.05
Age at first exposure, yearsc
No exposure	239	32	0.70	0.41–1.19	107	0.53	0.38–0.75		69	0.53	0.35–0.81
≥20	490	52	1		263	1			170	1
15–19	222	33	1.06	0.64–1.78	154	1.07	0.78–1.47	0.66	101	0.86	0.58–1.27
<15	219	27	1.13	0.66–1.94	139	1.04	0.75–1.44		124	1.25	0.86–1.82
Continuous			1.01	0.99–1.03		1.01	0.99–1.02	0.39		1.00	0.99–1.01
According to first full-term pregnancy (FFTP)c
Only after FFTPd	232	35	1		141	1			92	1
Before (incl. no FTP)	725	79	0.66	0.41–1.07	435	0.83	0.61–1.13	0.22	311	0.84	0.58–1.22

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

^aAdjusted for age at censoring, birth cohort (≤1945; 1946–1959; ≥1960), 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 breast cancer family history (0;1st degree; 2nd degree)

^bP value for χ² heterogeneity test between ER-negative and ER-positive tumors

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

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