Risk factors for breast cancer: A case-control study of screen-detected breast cancer in Miyagi Prefecture, Japan |
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Authors: | Yuko Minami Noriaki Ohuchi Akira Fukao Shigeru Hisamichi |
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Affiliation: | (1) Division of Epidemiology, Miyagi Cancer Center Research Institute, 47-1 Nodayama, Medeshima-Shiode, Natori, 981-12, Japan;(2) Department of Public Health, Tohoku University School of Medicine, 2-1 Seiryomachi, Aoba-ku, Sendai, 980, Japan;(3) Second Department of Surgery, Tohoku University School of Medicine, 1-1 Seiryomachi, Aoba-ku, Sendai, 980, Japan |
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Abstract: | We examined the associations between reproductive factors and the risk of breast cancer on the basis of information from a total of 201,363 breast cancer screening program participants in Miyagi Prefecture, Japan, during 1987-1991. A case-control study method was applied on analysis. Data on 204 breast cancer cases identified and 810 screening year-, age- and screening area-matched normal controls were extracted. After adjustment for potential confounders, a trend of decreasing risk of breast cancer with increasing number of parity was observed (p for trend=0.03). Among parous women, lactation for the last child decreased the risk of breast cancer (odds ratio (OR) = 0.61, 95% confidence interval (95% CI) 0.39–0.94). These findings were consistent with those in clinical breast cancer reported previously. When cases were divided into two age groups, younger ( 49 y.o.) and older (50 y.o. ), family history of breast cancer among mother and sisters (OR=3.51, 95% CI 1.05–11.80), and lactation for the last child (OR=0.46, 95% CI 0.25–0.84) were associated with younger age breast cancer, whereas number of parity was associated with older age breast cancer (p for trend=0.03). The results by age group suggest that different mechanisms may exist in breast cancer developing at early and late onsets. |
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Keywords: | age breast cancer case-control study risk factors screening |
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