Breastfeeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers

Breast Cancer Research

Table 1 Baseline characteristics of breast cancer cases and controls with BRCA1 and BRCA2 mutations.

Characteristic	BRCA1			BRCA2
	Controls (n = 1,243)	Cases (n = 1,243)	P	Controls (n = 422)	Cases (n = 422)	P
Year of birth, mean (range)	1957.5 (1920-1980)	1957.3 (1920-1980)	0.71	1954.4 (1924-1978)	1955.3 (1924-1978)	0.82
Age at diagnosis, mean (range)	n/a¹	0.71	n/a¹	n/a¹	42.7 (24-67)	n/a¹
Country of residence, n (%)
Poland	601 (48%)	matched		0 (0%)	matched
USA	323 (26%)			187 (44%)
Canada	265 (21%)			218 (52%)
Israel	29 (2%)			13 (3%)
Austria	18 (1.5%)			3 (0.7%)
Italy	5 (0.4%)			0 (0%)
United Kingdom	2 (0.2%)			2 (0.5%)
Age at menarche, mean (range)	13.27(8-28)	13.09 (9-21)	0.003	12.64 (8-28)	12.15 (9-17)	0.88
Age at first birth, mean (range)	25.1 (15-44)	24.8 (15-42)	0.08	26.6 (17-44)	26.3 (16-42)	0.37
Age at last birth, mean (range)	29.3 (16-45)	29.0 (17-44)	0.06	30.5 (20-45)	30.2 (18-43)	0.96
Parity^2,4, n (%)
1	235 (19%)			65 (15%)
2	663 (53%)			233 (55%)
3	280 (23%)			100 (24%)
≥ 4	65 (5%)			24 (6%)
Mean (range)	2.16 (1-6)	matched		2.20 (1-6)	matched
Breastfeeding, mean months^3,4 (range)	10.4 (0-92)	8.8 (0-84)	0.0009	9.7 (0-94)	10.2 (0-86)	0.56
Oral contraceptive use⁴, ever, n (%)	644 (52%)	657 (53%)	0.95	348 (83.5%)	336 (80.2%)	0.22
Smoking status, ever, n (%)	549 (45%)	574 (46%)	0.74	185 (44.4%)	170 (40.9%)	0.31
Alcohol use, ever, n (%)	832 (67%)	760 (61%)	0.002	305 (73.3%)	284 (68.8%)	0.13
HRT use⁴, n (%)	148 (12%)	67 (5%)	< 0.0001	69 (16.5%)	45 (10.7%)	0.02
BMI at age 30, mean (range)	22.5 (13-47)	22.6 (9-62)	0.24	22.8 (15-54)	23.0 (12-65)	0.48

¹n/a, not applicable. ²Parity includes live births only. ³Breastfeeding is the total months of breastfeeding for each pregnancy combined. ⁴Parity, breastfeeding, oral contraceptive use and HRT use were censored one year prior to the diagnosis of the matched case for both cases and controls.

ISSN: 1465-542X