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The Sister Study

Cohort Description

Study Cohort

Cohort Description and Characteristics

The Sister Study was established by Drs. Dale Sandler and Clarice Weinberg at the National Institutes of Health / National Institute of Environmental Health Sciences, to discover environmental and genetic risk factors for breast cancer. The Sister Study cohort includes more than 50,000 women whose sister had breast cancer. On average, women with a sister with breast cancer have twice the risk of developing breast cancer themselves. Sisters also share potentially relevant gene variants and exposures. Thus, the Sister Study provides greater statistical power than a similar size general population cohort for studying gene and environment interactions.

The Sister Study launched in August 2003, enrolling volunteers without a history of breast cancer, aged 35-74, residing in the United States and Puerto Rico. Enrollment of the cohort of 50,884 closed in July 2009. Targeted recruitment strategies for minority, lower education, and older women were employed to enhance diversity within the cohort.

Baseline data collection included a comprehensive Computer Assister Telephone Interview (CATI), self-completed questionnaires, and a home visit. Exposure information was collected across the life course, including in utero, childhood, adolescence and adulthood.

INFORMATION COLLECTED DURING THE CATI INCLUDED:
  • Cancer history of sister(s)
  • Residential history and exposures
  • Occupational history and exposures
  • Reproductive history
  • Medical history and medications
  • Lifestyle factors
  • Socioeconomic characteristics
SELF-ADMINISTERED QUESTIONNAIRES INCLUDED:

Diet Questionnaire—

  • Block 98 FFQ
  • Childhood diet
  • Vitamins and supplements
  • Soy products
  • Dietary patterns

Family History Questionnaire –

  • Family cancer history
  • Mother’s pregnancy experience In utero and childhood exposures

Personal Care Products

Past 24 Hour Exposure Questionnaire

Samples collected during home visit included first morning void urine, blood, toenail clippings, and household dust. Home visits also included anthropometric and blood pressure measurements.

Participants are contacted annually for brief updates on health status and contact information. A comprehensive follow-up questionnaire is administered every two to three years for more detailed updates on lifestyle and health and to collect new information on special topics of interest. Additional information, including medical records, pathology reports, and tumor blocks, is sought for women reporting breast cancer or other diagnoses of interest.

The percentages for each characteristic may not add up to 100 due to rounding. The number of missing or not applicable were excluded from the total (N = 50,884) for calculating of percentages. 

Demographic Characteristics

Age (in years) of Participant
at Baseline Enrollment
Number of Participants Percentage
35-44
45-54
55-64
65 or older
6,578
17,520
17,912
8,874
13%
34%
35%
17%

 

Self-Reported Race/Ethnicity Number of Participants Percentage
White, non-Hispanic
Black, non-Hispanic
Hispanic
Other
Missing
42,558
4,462
2,515
1,334
15
84%
9%
5%
3%
--

 

Highest Education Level Attained Number of Participants Percentage
High school or less
Some college, no degree
Associate/technical degree
Bachelor's degree
Graduate degree
Missing
7,805
9,957
7,224
13,714
12,172
12
15%
20%
14%
27%
24%
--

 

Income Number of Participants Percentage
Less than $20,000
$20,000 - $49,999
$50,000 - $99,999
$100,000 - $200,000
More than $200,000
Missing
2,296
10,284
19,907
12,868
3,534
1,995
5%
21%
41%
26%
7%
--

 

Participant Reports a Mother Diagnosed with Breast Cancer Number of Participants Percentage
Yes
No
Missing
9,135
39,834
1,915
19%
81%
--

 

Participant Reports a Sister Diagnosed with Breast Cancer Number of Participants Percentage
1 sister with breast cancer
2 or more sisters with breast cancer
Missing
45,706
5,177
1
90%
10%
--

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Lifestyle Characteristics

Body Mass Index (BMI)
of Participant
Number of Participants Percentage
Underweight (less than 18.5)
Normal weight (18.5-24.9)
Overweight (25.0-29.9)
Obese (30.0 or more)
Missing
563
18,875
16,151
15,278
17
1%
37%
32%
30%
--

 

Smoking Status of Participant Number of Participants Percentage
Never smoked
Yes: past social smoker
Yes: current social smoker
Yes: past regular smoker
Yes: current regular smoker
Missing
27,397
1,045
58
18,141
4,175
68
54%
2%
Less than 1%
36%
8%
--

 

Alcohol Intake of Participant Number of Participants Percentage
Never consumed alcohol
Yes: Former drinker
Current drinker: less than 1 drink per day
Current drinker: 1 drink per day
Current drinker: 1.1 to 1.9 drinks per day
Current drinker: 2 or more drinks per day
Missing
1,949
7,730
34,256
1,237
3,160
2,465
87
4%
15%
67%
2%
6%
5%
--

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Reproductive Characteristics

Age (in years) when Participant's Periods Started Number of Participants Percentage
11 or younger
12-13
14 or older
Never menstruated
Missing
10,405
28,525
11,909
7
38
20%
56%
23%
--
--

 

Parity (number of live births) Reported by Participant Number of Participants Percentage
0 live births
1 live birth
2 live births
3 live births
4 live births
5 or more live births
Missing
9,246
7,442
18,868
10,124
3,482
1,687
35
18%
15%
37%
20%
7%
3%
--

 

Age (in years) of Participant at First Live Birth Number of Participants Percentage
19 or younger
20-24
25-29
30-34
35 or older
No Live Births
Missing
6,822
15,892
11,525
5,225
2,130
9,246
44
16%
38%
28%
13%
5%
--
--

 

Participant Reports Breastfeeding Child/Children Number of Participants Percentage
Yes: breastfed
No: never breastfed
Missing
28,945
21,904
35
57%
43%
--

 

Participant Reports Use of Hormonal Birth Control Number of Participants Percentage
Yes: used
No: never used
Missing
43,122
7,724
38
85%
15%
--

 

Menopausal Status of Participant at Time of Baseline Enrollment Number of Participants Percentage
Natural menopause
Surgical menopause
Premenopause
Unknown/missing
20,377
12,357
18,120
30
40%
24%
36%
--

 

Participant Reports Use of Hormone Replacement Therapy
(estrogen/progesterone)
Number of Participants Percentage
Yes: used
No: never used
Missing
23,050
27,675
159
45%
55%
--

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