Diagnostic chest X-rays and breast cancer risk among women with a hereditary predisposition to breast cancer unexplained by a BRCA1 or BRCA2 mutation

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	OR^a	95% CI	Cases	OR^a	95% CI	P^b	Cases	OR^a	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, years^c
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 FFTP^d	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

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