The most important risk factors for developing breast cancer include:

• Getting older 
• Having a strong family history of breast cancer 
• Having previously been diagnosed with breast cancer or ductal carcinoma in situ (DCIS)

Other factors that seem to slightly increase a woman's risk of developing breast cancer include:

• Starting menstruation, or "periods", at a relatively early age (before 12 years)  
• Starting menopause, or "change of life", at a relatively late age (after 55 years)  
• Not having children, or having a first child after 30 years of age  
• Not breastfeeding — the more months spent breastfeeding, the lower the risk of developing breast cancer  
• Taking combined Hormone Replacement Therapy (HRT) after menopause, especially when taken for five years or longer  
• Putting on a lot of weight in adulthood, especially after menopause  
• Drinking alcohol (more than two standard drinks a day)  
• Having previously been diagnosed with lobular carcinoma in situ (LCIS) or atypical hyperplasia (AH)

Learn more about:

• Breast Changes
• Early Detection
• Awareness Campaigns
• Screening for Breast Cancer and Ovarian Cancer

You can help reduce your risk of breast cancer by doing some simple things:

• Alcohol increases your risk of breast cancer. This includes beer, wine and spirits. Try to keep your consumption down to no more than two standard drinks a day
• Active women of all ages are at reduced risk of breast cancer compared to women who do not exercise. And the more exercise you do, the bigger the benefits
• Having children at a younger age (less than 30 years) can reduce your risk of breast cancer. The more children you have, the lower your risk
• Breastfeeding for a total of 12 months or longer can slightly reduce your breast cancer risk
• Not smoking

Note:
Despite these lifestyle factors, any woman can still develop breast cancer and breast symptoms should be reported to your doctor.

Information from NBOCC and Australian Family Cancer Clinics