Risk factors we can't change

Unfortunately, being a woman and getting older are the highest risk factors for developing breast cancer. 99% of all breast cancer cases occur in women, and around 75% of all breast cancer cases occur in women over 50 years. As a woman ages, its more likely that abnormal changes might occur in her breasts. Men can get breast cancer too, but their risk is much lower and they account for only 1% of all cases.

You have a higher risk of developing breast cancer if you’ve had breast cancer or some other breast conditions in the past.

These include:

• Breast cancer or DCIS
• Pre-cancerous breast conditions, e.g. lobular carcinoma in situ (LCIS)
• Proliferative breast disease, e.g. atypical ductal or lobular hyperplasia

Hereditary breast cancer is less common than most people think – only 5-10% of breast cancers can be explained by family history. Watch our webinar, Genetic Risk of Breast Cancer.

You may have a higher risk of developing breast cancer if:

• Your parent, sibling or child has had breast and/or ovarian cancer (especially if under 50 years of age)
• You have multiple close relatives affected by breast cancer (male or female) or ovarian cancer
• You have relatives who were diagnosed with breast cancer before menopause
• One of your relatives has had both breast and ovarian cancer
• You have relatives diagnosed with bilateral breast cancer (breast cancer in both breasts)
• You are of Ashkenazi (Eastern European) Jewish ancestry.

Breast cancer in your family? Find out about your own risk

Research has shown that there's a link between the length of time a woman produces oestrogen and the development of breast cancer. Oestrogen is produced by the ovaries (except during pregnancy and breastfeeding) before menopause and in fat tissue after menopause.

Exposure to oestrogen is increased by:

• Younger age at first menstruation (under 12).
• Older age at menopause (over 55).
• Having few or no pregnancies.
• Limited duration of breastfeeding or no breastfeeding: Breastfeeding limits oestrogen exposure by reducing the number of menstrual cycles.
• Late age at first childbirth: Women who have their first child after 30 years of age have been producing oestrogen continuously for longer. Research shows that a possible contributing factor to the worldwide increase in breast cancer incidence over the last decade or so is women commonly having their first child after 30. In previous decades, women were pregnant often at an earlier age, and had multiple births over several years. As a result, they experienced fewer menstrual cycles, and their length of time exposed to oestrogen was reduced.

Some women have a higher proportion of dense glandular breast tissue and fibrous connective tissue compared to fatty tissue in their breasts. Increased density can’t be felt in the breast but can be seen on a mammogram.

This can be a risk factor for breast cancer and make it harder for a mammogram to detect tumours. When you have your mammogram, ask your radiologist about your breast density and how best to screen or monitor your future breast health if your density is high.

Maori and Caucasian women have a higher incidence of breast cancer than Pacific and Asian women in New Zealand. Maori women have a 35% higher incidence than non-Maori women.

Women and men who have had chest radiation treatment as children or young adults, for diseases such as lymphoma, are at increased risk of developing breast cancer. Patients who had this treatment can have breast screening provided by their DHB or BreastScreen Aotearoa .

For reasons that are not completely understood, being taller slightly increases breast cancer risk.