NONMODIFIABLE RISKS

Female gender: 100x risk compared to men

Age over 55: 2/3 breast cancers found in women over 55

BRCA inheritance: 5 to 10% cases are heritable; BRCA1 mutation lifetime risk 55 to 80%; BRCA2 mutation lifetime risk 45%; BRCA mutation increases risk of breast cancer at young age, bilateral breast cancer, and ovarian cancer

Lobular carcinoma in situ (LCIS): Marker for future breast cancer development; 7 to 10x risk compared to women without LCIS

High-risk breast disorders (ex: ADH, LN): 3.5-5x average risk

1st degree relative with h/o breast cancer: increases risk 2x

Increased estrogen action on breast tissue:

– Higher # lifetime menstrual periods: Menarche before age 12, menopause after age 55, nulliparous/first child after age 30-35: risk increases proportionately with # of lifetime periods

– DES exposure: Personal or maternal use (used 1940-1960 to prevent miscarriage) slightly increases risk

Dense breasts: 1.2 to 2x risk and more likely to miss small lesions on mammography

Race: White > Black > Asian, Hispanic, Native American

Chest radiation before age 40: Higher risk with younger age at exposure to radiation

MALIGNANT BREAST DISORDERS:

Epidemiology and Risk Factors

MODIFIABLE RISKS

Post-menopausal combined HRT: Increases breast cancer risk and mortality

Alcohol: 2 to 5 drinks per day leads to 1.5x average risk

Nulliparity or 1st child born after age 30: Slightly increased risk; however, pregnancy itself slightly increases risk of triple-negative breast cancer

Birth control: Use of OCPs (past 10 years) or DMPA (past 5 years) slightly increases risk compared to women who have never used these

BMI > 25 after menopause: Increased risk of breast cancer via increased exposure to estrogen produced by adipose tissue and/or increased exposure to insulin; worse with new weight gain after menopause and central obesity

NEGATIVE RISKS

Physical activity: 1.25 to 2.5 hours of brisk walking per week reduces breast cancer risk by 18%, benefit increases with walking 10 hours per week

Extended breastfeeding: 1.5 to 2 years slightly lowers breast cancer risk (by reducing total number of menstrual cycles)