However, 250, 000 breast cancers will occur in this group over their lifetimes owing to the 1% lifetime incidence of breast cancer.

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But this research linked other oils -- like those found in margarine, fried and baked goods and salty snacks that contain so-called trans-fatty acids -- to a higher incidence of breast cancer.

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Although women in their 40s have a lower incidence of breast cancer compared with older women, the window to detect tumors before they become symptomatic is shorter (2 to 2.4 years) compared with women ages 70 to 74 (4 to 4.1 years), the authors of the ACOG guidelines said.

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In a study of 288 women from 2001, the drug tamoxifen reduced breast-cancer incidence among healthy BRCA2 carriers by 62% compared with a placebo, though it didn't reduce breast-cancer incidence among healthy women with BRCA1 mutations.

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