Risk factors and causes of DCIS

The risk factors for DCIS and invasive breast cancer are similar. It’s not clear exactly what causes breast cancer but different things can increase a woman’s risk of developing it. These include:

  • Increasing age – the risk of DCIS increases with age. It’s rare in women under the age of 35.
  • Previous breast cancer and some non-cancerous (benign) breast conditions – having one of these can increase the risk.
  • Dense breast tissue – women are slightly more likely to develop cancer when the breasts have more glandular and connective tissue, with very little fatty tissue.
  • Not having children – women who haven’t had children are slightly more likely to develop breast cancer than women who have.
  • Not breastfeeding – women who have never breastfed are slightly more at risk than women who have breastfed for more than a year.
  • Early periods or a late menopause – women whose periods started before they were 12 or who’ve had a late menopause (after the age of 50) are at a slightly higher risk.
  • Hormone replacement therapy (HRT) – this reduces some effects of menopause but can increase the risk of breast cancer. You can talk to your GP about the benefits and possible risks of taking HRT.
  • Lifestyle factors – being overweight after the menopause and drinking more than two units of alcohol a day over many years can slightly increase risk. Smoking heavily from a young age can also increase risk.

Family history and risk

Most women diagnosed with breast cancer don’t have any family history of it. Only a very small number of women with breast cancer have a gene that greatly increases the risk of breast cancer. The two genes most often found in hereditary breast cancer are called BRCA1 and BRCA2.

Generally, the chance of breast cancer being hereditary is greater when:

  • a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer
  • these family members are closely related to you
  • these family members were diagnosed at a young age.