These are the convincing risk factors for developing breast cancer (Cancer Australia 2018) (those highlighted in bold are modifiable):

• age
• gender (being female)
• significant family history of breast cancer and/or other cancers
• pathogenic variants in cancer predisposition genes including BRCA1, BRCA2, CDH1, PALB2, PTEN, NF1, STK11, TP53, ATM and CHEK2
• DCIS (ductal carcinoma in situ)
• LCIS (lobular carcinoma in situ) also referred to as non-invasive lobular neoplasia
• atypical epithelial proliferative lesions (atypical ductal hyperplasia and atypical lobular hyperplasia)
• previous breast cancer
• high mammographic breast density (must be adjusted for age and body mass index)
• early menarche
• not bearing children
• never having breastfed
• late age at first birth
• late menopause
• maternal exposure to diethylstilboestrol (DES) in utero
• use of combined hormone replacement therapy, particularly for extended periods over many years
• not engaging in adequate physically active
• overweight and obesity (only for postmenopausal women)
• weight gain (postmenopausal)
• alcohol consumption
• exposure of the breast to ionising radiation.

For more information, visit the Cancer Australia breast cancer risk factor website.

Recommendations that may assist in preventing breast cancer include:

• maintaining a healthy weight
• avoiding or limiting alcohol intake to no more than 10 standard drinks a week and no more than four standard drinks on any one day
• getting 30 minutes or more of moderate-intensity (puffing) exercise most days (150–300 minutes per week)
• avoiding or limiting hormone replacement therapy use
• additional prevention strategies in people with increased risk (e.g. gene mutation carriers).

Additional prevention interventions are considered for women at increased risk, including those at moderately increased risk. For example, those at moderately increased risk (1.5–3 times the population risk) may be offered medication to reduce risk, and those at high risk (more than three times the population risk) may be offered medication or risk-reducing surgery.

Everyone should be encouraged to reduce their modifiable risk factors (see section 1.1).

By accurately assessing a woman’s personal breast cancer risk level, health professionals can offer the most appropriate evidence-based prevention and early detection strategies. All women should therefore consider having their individual breast cancer risk assessed. This can be done by women themselves or in primary care. Cancer risk assessment should be repeated when major risk factors change (e.g. new family cancer history, breast biopsy showing atypical hyperplasia or LCIS).

There are a number of validated computerised breast cancer risk assessment tools that estimate a woman’s breast cancer risk based on her individual risk factors:

• iPrevent
• IBIS tool
• CanRisk Web Tool

iPrevent is an Australian tool designed for self-administration by women and collaborative use with clinicians and is the only tool that links the risk assessment directly to the relevant risk management guidelines.

In Australia, absolute lifetime population risk of breast cancer is 12 per cent, but most women are below this risk. Cancer Australia defines levels of breast cancer risk as follows:

• average risk: < 1.5 × population risk
• moderate risk: 1.5–3 × population risk
• high risk: > 3 × population risk (Cancer Australia 2010).

People with or without a personal history of breast cancer at high risk due to their family cancer history should be referred to a familial cancer service for further risk assessment and for possible genetic testing (eviQ 2019a). Consider referring:

• untested adult blood relatives of a person with a known pathogenic variant (mutation) in a breast and/or ovarian cancer predisposition gene (e.g. BRCA1 or BRCA2, TP53, PTEN, STK11, PALB2, CDH1, NF1) or
• people with two first- or second-degree relatives diagnosed with breast or ovarian cancer plus one or more of the following on the same side of the family:
• additional relative(s) with breast or ovarian cancer
• breast cancer diagnosed under age 50 years
• more than one primary breast cancer in the same woman
• breast and ovarian cancer in the same woman
• Jewish ancestry
• breast cancer in a male
• pancreatic cancer
• high-grade (≥ Gleason 7) prostate cancer.

Additionally, people with breast cancer should be referred to a familial cancer service if they meet the following criteria:

• male breast cancer at any age
• breast cancer and Jewish ancestry
• two primary breast cancers in the same person, where the first occurred under age 60 years
• two or more different but associated cancers in the same person at any age (e.g. breast and ovarian cancer)
• breast cancer aged under 40 years or triple-negative breast cancer aged under 50 years
• lobular breast cancer and a family history of lobular breast or diffuse-type gastric cancer
• breast cancer aged under 50 years with limited family structure or knowledge (e.g. adopted)
• breast cancer and a personal or family history suggestive of:
• Peutz-Jegher syndrome (oral pigmentation and/or gastrointestinal polyposis)
• PTEN hamartoma syndrome (macrocephaly, specific mucocutaneous lesions, endometrial or thyroid cancer)
• Li-Fraumeni syndrome (breast cancer < 50 years, adrenocorticocarcinoma, sarcoma, brain tumours).

Referral can also be considered if finding a relevant germline mutation would have high clinical utility (e.g. would alter treatment of the current cancer).