Risk factors we can't change

The two biggest risks for breast cancer are non-modifiable, or things we cannot change. These include, being born female and ageing.

Gender

Over 99% of breast cancer cases occur in women. In NZ, approximately 25 men are diagnosed with breast cancer every year. While breast cancer can happen to men, women are at a much higher risk. 1 in 9 Kiwi women will be diagnosed with breast cancer in their lifetime.

Ageing

In New Zealand 3 out of every 4 diagnoses happen to women aged over 50. The average age at the time of diagnosis is 58. It’s important to know the normal look and feel of your breasts as you age and continue to have mammograms as part of the free national screening programme.

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.

Breast tissue is made up of fibroglandular tissue (glandular tissue and fibrous connective tissue that supports the breast) and fatty tissue. Dense breasts have more fibroglandular tissue, while non-dense breasts have more fatty tissue. Increased breast density can not be felt by touching your breasts, but it can be viewed on a mammogram.

10% of women have very dense breasts. Very dense breasts are classified as Grade D. For these women, breast tissue and breast cancers can both show up as white on a mammogram. This means breast cancers can be missed. If you know you have dense breasts, have a chat with your GP about additional screening options. 

• Breast density is influenced by genetics, age, weight, hormone treatments, ethnicity and physical activity.
• Breast density by itself is associated with a moderate risk of breast cancer.
• It is recommended women with high breast density have annual mammograms from age 40. 

It's important to be vigilant about touching and looking for breast changes, but especially if you have dense breasts.

Currently women who receive screening from Breast Screen Aotearoa are not told if they have dense breasts. We believe women should have this information so they can make informed decisions about their screening.

Breast density tends to reduce with age. Mammograms are not recommended for women under the age of 40 as these women are more likely to have dense breasts. 

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.