RESUMEN
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.
Asunto(s)
Neoplasias de la Mama/epidemiología , Neoplasias Primarias Secundarias/epidemiología , Historia Reproductiva , Adulto , Factores de Edad , Anciano , Lactancia Materna , Neoplasias de la Mama/patología , Estudios de Casos y Controles , Estudios de Cohortes , Dinamarca/epidemiología , Femenino , Número de Embarazos , Humanos , Entrevistas como Asunto , Modelos Logísticos , Menarquia , Menopausia , Persona de Mediana Edad , Invasividad Neoplásica , Neoplasias Primarias Secundarias/patología , Paridad , Embarazo , Sistema de Registros , Factores de Riesgo , Encuestas y Cuestionarios , Estados Unidos/epidemiologíaRESUMEN
OBJECTIVE: The available epidemiological evidence indicates that drinking alcohol per se is associated with breast cancer. However, it has not been investigated how the breast cancer risk for a given total alcohol consumption depends on the drinking frequency. METHODS: Within the prospective study on 'Diet, Cancer and Health', we examined the relationship between breast cancer, intake of total alcohol and frequency of drinking among 23,778 postmenopausal women, among whom 425 cases of breast cancer accrued during a median follow-up of 4.8 years. RESULTS: The dose-response relationship between total alcohol intake and breast cancer showed an increase in the rate ratio of 1.10 per 10 g/day (95% CI: 1.04-1.16) with no evidence for differences by type of alcohol beverage. No interaction was found between drinking frequency and total alcohol intake in the risk of breast cancer (p = 0.40). CONCLUSIONS: The present study supports previous ones in showing a monotonic increase in the risk of breast cancer among postmenopausal women with increasing average daily intake of alcohol, and this relationship with alcohol intake did not depend on drinking frequency.