Table 5.

Familial risk factors for breast and/or ovarian cancer in Sister Study participants at baseline, 2003–2009.

Characteristic	$n$	Frequency (%)a
Participants	50,884	100.0
First-degree female relatives with  breast cancerb
0	1,709	3.4
1	36,377	71.5
$\ge 2$	12,795	25.1
Missing	3
First-degree female relatives with  young-onset breast cancerb,c
0	21,563	43.0
1	25,910	51.6
$\ge 2$	2,703	5.4
Missing	708
Sisters with breast cancer
1 half-sister, no full sisters	1,905	3.8
1 full sister, no half-sisters	43,736	86.1
1 sister (unknown if half or full)	28	0.1
2 half-sisters	136	0.3
2 sisters (1 full and 1 half)	275	0.5
2 full sisters	4,096	8.1
2 sisters (1 or both half or unknown)	7	0.01
$\ge 3$ sisters (half, full, or unknown)	629	1.2
Missing	72
Mother had breast cancer
Yes	9,135	18.7
Missing	1,915
First-degree relatives with ovarian cancerb
0	48,858	96.1
$\ge 1$	1,994	3.9
Missing	32
Mother had ovarian cancer
Yes	1,157	2.4
Missing	1,917
First-degree family history of breast  and ovarian cancer
Yes	1,940	3.8
No	48,912	96.2
Missing	32
Ever been tested for BRCA1 or BRCA2
Yes	1,551	3.1
No	49,094	96.9
Missing	239
Told you have a mutation in one of the  breast cancer genes
Yes	256	17.3
No	1,223	82.7
Missing	72
Gail score
5-y absolute risk
$\le 1.66\%$	8,371	16.5
$\ge 1.67\%$	42,399	83.5
Missing	114
Median (range)	2.8 (0.2–14.3)
Lifetime (90 y) absolute risk
$<15\%$	17,174	33.8
$15–<20\%$	17,107	33.7
$\ge 20\%$	16,489	32.5
Missing	114
Median (range)	17.1 (2.4–61.2)

^aTotal percentages may not always equal 100% due to missing values and rounding.

^bDoes not include half-sisters (second-degree relatives).

^cYoung onset defined as diagnosed at $<50\mathrm{y}$ of age.