What are the causes of breast cancer?

About 50% of women have no identifiable risk factors. Risk factors include:

Age
The risk of developing breast cancer increases with age. 70% of breast cancers occur in women above 40 years old.

Family history
Having a first degree relative (sister, mother, maternal grandmother) who has breast cancer doubles the risk. Women with such a first degree relative should start breast screening early, at about 35 years of age

Genes
Women with BRCA1 and BRCA2 genes have a 40 to 60% lifetime risk of developing breast cancer. However, this forms only 1% of female breast cancer patients.

Reproductive history
- Women who have never given birth
- Women who had their first child after 35 years old

Menstrual history
- Early onset of menses - below 11 years old
- Late menopause - above 55 years old

Diet
- Alcohol - 2 glasses of alcohol daily increases risk by 1.5 times
- Soy products (soya bean) reduces risk of breast cancer
- Omega 3 fish oil reduces risk of breast cancer
- Vitamin A, C, E and selenium protects against breast cancer

Body weight
Obesity increases breast cancer risk and increases the body's oestrogen levels

Physical exercise
It reduces risk of breast cancer and lowers body's oestrogen levels

Hormones
Hormone Replacement Therapy (HRT) - increases risk of breast cancer by 30% but the risk disappears 3 to 5 years after stopping HRT

Past history of breast cancer increases risk of cancer in opposite breast

Dr Christopher Ng is an obstetrician gynaecologist in private practice.

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