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.