Table 6

Studies assessing the association of twinship with risk for breast cancer

Type of study

Ref.

Year

Design

Cases

Controls (or cohort)

Country/place of study

Category

OR (95% CI)

Comments


Case-control studies

[63]a

1992

MCC

870

2,741

UK, USA

Singleton

Referent

Adjusted for age, study center, parity, age at first birth, age at menarche, height, body mass index, maternal age at birth, birth order, and menopausal status

Twinship

1.40 (0.77–2.55)

Singleton

Referent

Monozygote twin

1.30 (0.58–2.92)

Dizygote twin

1.54 (0.64–3.71)

[14]

1996

PCC

1,134

1,380

USA

Age 21–45

Adjusted for age, menopausal status, and maternal smoking

Singleton

Referent

Twinship

0.6 (0.3–1.3)

Age 50–64

Singleton

Referent

Twinship

0.9 (0.4–2.2)

[58]a

1997

PCC

2,150

1,961

USA

Singleton

Referent

Adjusted for age, study site, family history of breast cancer, breast biopsy, a combination variable including number of full-term births and age at first full-term pregnancy, age at menarche, menopausal status, body mass index, average lifetime alcohol consumption, and the number of mammograms

Twinship

1.6 (1.0–2.7)

Singleton

Referent

Monozygote twin

1.39 (0.7–2.6)

Dizygote twin

2.06 (1.0–4.5)

[32]

1997

NCC

1,068

2,727

Sweden

Singleton

Referent

Adjusted for maternal age, matermal socioeconomic status, maternal parity, maternal pre-eclampsia or eclampsia, neonatal jaundice, severe prematurity, twin, and birth weight

Twinship

1.3 (0.8–2.1)

Singleton

Referent

Monozygote twin

0.7 (0.2–2.2)

Dizygote twin

1.5 (0.8–2.7)

[15]

2000

LCC

481

2,863

USA

Singleton

Referent

Crude ORs

Twinship

1.04 (0.51–2.11)

[43]

2001

LCC

319

768

USA

Singleton

Referent

Crude ORs

Twinship

1.6 (0.2–10.1)

[45]

2004

LCC

2,522

10,052

USA

Singleton

Referent

Adjusted for age and maternal age at first birth

Twinship

1.77 (1.05–2.97)

[20]

2005

PCC

2,338

2,476

Poland

Singleton

Referent

Adjusted for age, education, age at menarche, menopausal status and age at menopause, age at first full-term pregnancy, number of full-term pregnancy, family history of breast cancer among first-degree relatives, mammography screening, and current body mass index

Twinship

0.76 (0.49–1.16)

Singleton

Referent

Monozygote twin

0.90 (0.53–1.52)

Dizygote twin

0.58 (0.23–1.47)


Cohort studies

[64]

1980

LTCohort

270

(16,922)

Denmark

Twinship

1.1 (1.0–1.2)

Observed/expected ratio (95% CI)

[65]

1995

LTCohort

740

(25,541)

Sweden

Twinship

1.1 (1.0–1.1)

Observed/expected ratio (95% CI)

Monozygote twin

1.0 (0.9–1.2)

Dizygote twin

1.1 (1.0–1.2)

[67]

1999

LTCohort

245

(13,176)

Finland

Twinship

0.91 (0.81–1.00)

Observed/expected ratio (95% CI)

Monozygote twin

0.76 (0.59–0.97)

Dizygote twin

0.98 (0.84–1.10)

[66]

2000

Cohort

1,230

(29,197)

USA

Singleton

Referent

Adjusted for age, education, family history of breast cancer, age at menarche, age at first birth, height, current body mass index, body mass index at age 18, waist:hip ratio, alcohol drinking, and hormone replacement therapy

Twinship

1.72 (1.22–2.42)

Singleton

Referent

Monozygote twin

1.04 (0.43–2.5)

Dizygote twin

1.77 (1.16–2.7)

[31]

2006

Cohort

249

1,024

USA

Singleton

Referent

Adjusted for age at diagnosis, diagnosis year, stage at diagnosis, and birth order, with exception of birth order, which is adjusted for maternal age

Twinship

2.5 (1.0–6.2)


aAuthors used the female twins as the proxy of the monozygote twin and the female twin with male twin as the proxy of the dizygote twin. Cohort, cohort study; LCC, case-control study with linkage with population and cancer registry data; LTCohort, twin cohort study by using linkage with birth and cancer registry data; MCC, multicenter case-control study; NCC, nested case-control study in cohort; PCC, population-based case-control study.

Park et al. Breast Cancer Research 2008 10:R8   doi:10.1186/bcr1850

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