Epidemiological data indicate well-defined factors increase the liability to
develop the disease called relative risk (RR)


A-Major risk factor:
I. Age
- Carcinoma of breast is extremely rare below age of 20 years.
- Mean age of affection is 60 years.
- By the age of 90y nearly 20% of females are affected.
2. Sex
1) Breast cancer is 100 times more common in women than in men 
3. Family history
a) lt has been proven that 5 - 10 % of breast cancers are due to mutation in
suppressor genes (autosomal inheritance)
1. Mutation in 2 suppressor genes:
BRCA-I (on chromosome 17) & BRCA-ll (On chromosome 13)
It usuallv occurs: at any age
                           multifocal &bilateral
2. Mutation in tumor suppressor gene P53: producing Li Fraumeni $ 
- Breast cancer. - Ovarian cancer.
- Carcinoma of the colon. - Lymphoma (or leukemia).
b) Positive family history increase the risk  :
-In mother and sister..... increase the risk 2.3 times.
-In both mother and sister..... increase the risk 16 times.
-20% of breast cancer are familial.
4. Previous affection with cancer breast
- Patient with breast cancer in one side.......increase the risk to develop cancer in the other breast (cases of lobular carcinoma in situ RR 10).
- Bilateral breast cancer occurs in about 15 -20 %(Up to 25 - 50 o/o if nlobular carcinoma)
5. Nulliparity
 Breast cancer is commoner in single & nulliparous women 
6. Precancerous lesion
1) Duct papilloma (especially if multiple) ...increase the risk 1.5 - 2 times.
2) Lobular carcinoma in situ increase the risk by 5 - 10 times and it does not cause microcalcifications.
B-Intermediate risk factor:
1-Age of menarche & menopause
- Early menarche"age at first menstruation" (< 12 years) (RR 2.3).
- Late menopause"age at stop menstruation" (> 50 years)
2-Radiation therapy to the chest
- Women who had radiation therapy to the chest (including breasts) before age of 30 are at an increased risk of cancer breast e.g. Mantle radiotherapy in treatment of Hodgkin disease.
3-Obestty
- As there is peripheral conversion of steroid hormones into estradiol (E1) by aromatase enzyme in fatty tissues.
4-Benign breast dlseases
- Atypical epithelial hyperplasia increase  the risk 2 - 5 times.
C. Minor risk factors 
1-Alcoholic intake: 2. oral contraceprtive pills" hormonal replacement therapy" (HRT):
- Long term exposure to combined preparations of HRT does significanlly increase risk of developing breast cancer.
3-physical activity:
- Women who are physically inactive have an increased risk of breast caner,because physical activities and exercise may help to reduce risk by preventing weight gain.