Parity and breast cancer risk among BRCA1 and BRCA2mutation carriers

Breast Cancer Research

Table 2 Results from weighted Cox regression analysis

Parameter	All				BRCA1 carriers				BRCA2 carriers
	UN	BC	HR	95% CI	UN	BC	HR	95% CI	UN	BC	HR	95% CI
Parity
Nulliparous	37	65	1.00		25	37	1.00		12	28	1.00
Parous	295	392	0.54	0.37–0.81	193	211	0.53	0.34–0.83	102	181	0.58	0.27–1.24
Parity by attained age
≤40 years
Nulliparous	28	44	1.00		21	24	1.00		7	20	1.00
Parous^a	76	127	1.01	0.58–1.76	50	76	1.17	0.55–2.52	26	51	0.72	0.42–1.24
>40 years
Nulliparous	9	21	1.00		4	13	1.00		5	8	1.00
Parous	219	265	0.44	0.23–0.84	143	135	0.34	0.16–0.70	76	130	1.21	0.37–3.92
Number of live births^b
Nulliparous	37	65	1.00		25	37	1.00		12	28	1.00
1	46	57	0.62	0.37–1.02	27	34	0.62	0.34–1.11	19	23	0.58	0.22–1.53
2	109	167	0.57	0.38–0.86	73	80	0.54	0.33–0.87	36	87	0.68	0.31–1.47
3	66	79	0.64	0.34–0.86	42	50	0.56	0.33–0.97	24	29	0.44	0.19–1.04
4+	56	82	0.55	0.34–0.91	42	44	0.51	0.29–0.89	14	38	0.71	0.27–1.88
Per live birth			0.90	0.80–1.00			0.89	0.78–1.01			0.93	0.75–1.14
Age at first live birth
<20 years	61	55	1.00		38	35	1.00		23	20	1.00
20–24 years	132	179	1.16	0.76–1.78	85	92	1.08	0.65–1.78	47	87	1.74	0.87–3.49
25–29 years	106	108	1.13	0.72–1.79	73	66	1.08	0.64–1.52	33	42	1.48	0.68–3.22
≥ 30 years	39	50	1.30	0.74–2.29	25	18	0.83	0.42–1.64	14	32	4.77	2.08–10.94
Nulliparous	37	65	2.09	1.26–3.45	25	37	1.96	1.10–3.52	12	28	2.85	1.13–7.15

UN, unaffected carriers; BC, breast cancer; HR, hazard ratio; CI, confidence interval. ^aAnalyses not adjusted for oophorectomy (all others adjusted). Overall analysis stratified by year of birth and gene. ^bAssuming that births between first and last birth were equally spaced; 25 carriers (7 affected, 18 unaffected) with missing age at last birth were assumed to be nulliparous until age at first birth and were then considered as a separate category (hazard ratios not shown).

ISSN: 1465-542X