Reproductive history and risk of second primary breast cancer: the WECARE study.
BACKGROUND
Women with an initial breast cancer diagnosis are at elevated risk of developing subsequent cancer in the contralateral breast. Studies of reproductive factors and contralateral breast cancer (CBC) have provided inconsistent results.


METHODS
We employed a case-control study nested within five population-based cancer registries in the United States and Denmark to examine associations between reproductive history and CBC risk. Cases were women with asynchronous CBC who had their first primary invasive breast cancer before age 55 years. Two controls, who had only one primary breast cancer diagnosis, were individually matched to each case on age and year of diagnosis, race, and registry. A total of 694 case-control triplets and 11 case-control pairs were enrolled. Information regarding possible CBC risk factors was obtained via telephone interviews. Multivariable conditional logistic regression was used to estimate rate ratios (RR) and 95% confidence intervals (95% CI) associated with risk factors of interest.


RESULTS
Increasing number of full-term pregnancies (FTP) was inversely associated with CBC risk (P trend, 0.001). Women who reported menarche before age 13 years had an increased risk of CBC (RR, 1.26; 95% CI, 1.01-1.58). Age at first FTP, breastfeeding history, and age at menopause were not significantly associated with CBC risk.


CONCLUSIONS
These results suggest age at menarche and parity, which are established risk factors for first primary breast cancer, are associated with CBC, whereas other reproductive risk factors associated with first primary breast cancer, such as age at first FTP, are less important factors in the development of CBC.
Largent
Joan A
JA
Epidemiology Division, Department of Medicine, University of California, Irvine, Irvine, CA 92697-7555, USA. jlargent@uci.edu
Capanu
Marinela
M
Bernstein
Leslie
L
Langholz
Bryan
B
Mellemkaer
Lene
L
Malone
Kathleen E
KE
Begg
Colin B
CB
Haile
Robert W
RW
Lynch
Charles F
CF
Anton-Culver
Hoda
H
Wolitzer
Abigail
A
Bernstein
Jonine L
JL
D000328:Adult; D000367:Age Factors; D000368:Aged; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000473:pathology; D016022:Case-Control Studies; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D020073:Gravidity; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008572:Menarche; D008593:Menopause; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D016609:Neoplasms, Second Primary / Q000453:epidemiology* / Q000473:pathology; D010298:Parity; D011247:Pregnancy; D012042:Registries; D017584:Reproductive History; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology