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 6 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 gene group

	Number of				Number of				Number of				P^b
	Cases	Ctrls	OR^a	95% CI	Cases	Ctrls	OR^a	95% CI	Cases	Ctrls	OR^a	95% CI
	Gene group
	Group “Low”^f				Group “No Effect”^f				Group “High”^f
Chest X-ray exposure
No	34	67	1		61	81	1		65	91	1
Yes	234	371	2.02	1.16–3.52	354	416	1.62	1.03–2.55	495	400	3.31	2.14–5.12	0.0038
Number of exposures
0	34	67	1		61	81	1		65	91	1
<10	119	183	2.01	1.12–3.59	184	215	1.53	0.95–2.46	256	219	2.98	1.89–4.70
≥10	47	75	2.19	1.09–4.40	67	85	2.04	1.14–3.66	94	78	3.88	2.23–6.75	0.022
Continuous			1.02	0.99–1.04			1.02	1.00–1.04			1.04	1.02–1.06	0.032
Age at first exposure, years^d
No exposure	34	67	0.55	0.30–1.01	61	81	0.83	0.51–1.37	65	91	0.38	0.23–0.61	0.43
≥20	90	163	1		124	188	1		179	180	1
<20	101	143	1.24	0.80–1.91	166	165	1.38	0.94–2.03	222	159	1.27	0.90–1.80
Continuous			1.00	0.9–1.02			0.99	0.98–1.01			1.00	0.98–1.01	0.78
According to first full-term pregnancy (FFTP)^d
Only after FFTP^e	52	75	1		68	91	1		95	92	1
Before (incl. no FTP)	142	242	0.82	0.49–1.38	231	271	0.90	0.57–1.40	311	257	1.04	0.69–1.57	0.48

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), plus two other DNA repair rare variants groups (when analysis by group of DNA repair rare variants), with missing included in reference categories for each variable
^bBecause of the non-exclusivity of the 3 groups, P value for heterogeneity test was performed on the ranked Group variable : at least 1 variant in Group “High,” no variant in Group “High,” and at least 1 variant in Group “No Effect,” only at least 1 variant in Group “Low”
^dAdjusted as in ^a plus number of exposures (≤5;>5)
^eAfter = also includes chest X-ray exposure that occurred during the same year of first full-term pregnancy
^fIndividuals carrying at least one variant in one of the Gene Groups: Group “Low” (OR<0.9) ; Group “No Effect” (0.9<=OR<=1.1); Group “High” (OR>1.1)

ISSN: 1465-542X