Breast Cancer Causes and Risk Factors

The main risk factors

The greatest risk factors for breast cancer are being female and getting older. Most breast cancers (around 80%) are diagnosed in women over 50. Beyond these, the established risk factors include:

• Family history — particularly if a close relative (mother, sister, daughter) has had breast cancer, especially before 50
• Inherited gene mutations — particularly BRCA1, BRCA2 and PALB2
• Dense breast tissue — makes mammograms harder to interpret and is an independent risk factor
• Previous breast cancer or ductal carcinoma in situ (DCIS)
• Hormone replacement therapy (HRT) — particularly combined (oestrogen + progestogen) HRT
• Starting periods at an early age or having a late menopause
• Not having children, or having your first child after age 30
• Alcohol consumption — risk increases with every unit consumed regularly
• Being overweight or obese after the menopause
• Lack of physical activity

Inherited gene mutations

Around 5–10% of breast cancers are caused by an inherited fault in a gene. The most common faults are in the BRCA1 and BRCA2 genes. A woman who carries a faulty BRCA1 gene has a lifetime risk of breast cancer of around 65–80%. For BRCA2, the figure is around 45–60%. The PALB2 gene also significantly raises risk when faulty.

Genetic testing is available on the NHS for people at high risk. If you have two or more close relatives with breast or ovarian cancer, or a close relative diagnosed under 40, speak to your GP about a referral for genetic counselling.

Factors that lower risk

• Maintaining a healthy weight after the menopause
• Being physically active — at least 150 minutes of moderate exercise per week
• Breastfeeding — the longer you breastfeed, the greater the protective effect
• Limiting alcohol — the safest approach is not to drink at all
• Attending regular NHS screening when invited

Myths — what does NOT cause breast cancer

• Underwired or tight bras — no evidence
• Antiperspirant or deodorant — no evidence
• Trauma or injury to the breast — an injury may draw attention to a pre-existing lump, but does not cause cancer
• Mobile phones or electrical pylons — no conclusive evidence
• Stress — while stress has many health effects, no causal link to breast cancer has been established

Around 23% of UK breast cancers are estimated to be linked to lifestyle factors that could potentially be modified — mainly alcohol, weight, physical activity and not breastfeeding. This is significant, but it also means that the majority of breast cancers are not caused by lifestyle choices.

Alcohol and breast cancer risk

Alcohol is the most significant modifiable lifestyle risk factor for breast cancer. The risk increases with every additional unit consumed regularly — there is no known safe level of alcohol when it comes to breast cancer risk. Compared with non-drinkers, women who drink around two units of alcohol per day (roughly one standard glass of wine) have approximately 8% higher breast cancer risk. The more alcohol consumed, the greater the risk. The NHS and Cancer Research UK both advise that reducing or cutting out alcohol is one of the most effective evidence-based steps a woman can take to reduce her breast cancer risk.

Diet and breast cancer risk

The relationship between diet and breast cancer is complex, but the evidence points to some consistent patterns. Being overweight or obese after the menopause significantly raises risk — fat tissue produces oestrogen, which can fuel hormone receptor-positive breast cancers. Diets high in saturated fat and processed foods are associated with obesity and may independently raise risk. A Mediterranean-style diet — rich in vegetables, fruit, pulses, whole grains and olive oil, with limited red and processed meat — is associated with better overall cancer outcomes. However, no single food has been proven to prevent breast cancer, and the evidence for specific dietary supplements is weak.

Is breast cancer hereditary?

Around 5–10% of breast cancers are caused by an inherited faulty gene — most commonly BRCA1, BRCA2 or PALB2. A woman carrying a faulty BRCA1 gene has a lifetime breast cancer risk of approximately 65–80%. However, the great majority of breast cancers (90–95%) are not hereditary — they arise from acquired genetic mutations that develop during a person's lifetime rather than from mutations inherited at birth. Having a family history of breast cancer raises risk, but most women with a family history do not develop breast cancer, and most women who develop breast cancer have no family history. Speak to your GP if two or more close relatives have had breast or ovarian cancer, particularly if diagnosed before the age of 50.