1. Being a woman over 50
Risk factors we can't change
: This is the highest risk factor for developing breast cancer. Around 75% of all breast cancer cases occur in women over 50 years. Men can get breast cancer too but only account for 1% of all cases. As a woman ages, it’s more likely that abnormal changes may occur in her breasts..
2. Family history
: About 5-10% of breast cancers can be explained by family history; however, 90-95%, of women who develop breast cancer do not have a family history. You may have a higher risk of developing breast cancer if:
- Your mother, sister or daughter has had breast and/or ovarian cancer (especially if she is <50 years of age).
- Multiple close relatives affected by breast cancer (male or female) or ovarian cancer
- Relatives who were diagnosed with breast cancer pre-menopause
- Breast and ovarian cancer diagnosed in the same relative
- Relatives diagnosed with bilateral breast cancer
- Ashkenazi Jewish ancestry
Family history (5-10% of breast cancers) does not necessarily imply an inherited genetic cause, as 1-5% of women diagnosed have the true genetic/hereditary link (approximately 25-125 women in NZ annually).
This means these women are carriers of an inherited/faulty gene, such as the BRAC1 or BRAC2 genes. If you have inherited a fault in one of these genes, you have a high chance of developing breast or ovarian cancer; however, it does not mean that you are certain to develop either. For a BRAC1 gene mutation, the lifetime risk of breast cancer is 50-80% and for a BRAC2 gene mutation 40-70%. Of note, a BRAC1 or BRAC2 gene mutation can be inherited from either parent.
For information on genetic testing for breast cancer, The NZBCF recommends you firstly discuss genetic testing with your family doctor. If genetic testing is considered appropriate by your family doctor, your family doctor or yourself can phone a counselor at NZ Genetic Services (free service to NZ residents and citizens):
- Northern Region 0800 476 123 (toll free)
- Central Region 0508 364 436 (toll free)
- Southern Region 0508 364 436 (toll free)
Even if no one in your family has been diagnosed with breast or ovarian cancer, it is most important for you to follow the Foundation's ‘Priorities in Breast Awareness
Find out more about Inherited Breast Cancer and genetic testing.
3. Previous breast issues
: You have a higher risk of developing breast cancer if you’ve had breast cancer or other breast conditions in the past. These may include:
• Breast cancer
• Pre-cancerous breast conditions, e.g. lobular carcinoma in situ (LCIS)
• Benign breast disease, e.g. atypical ductal hyperplasia
• Radiation treatment of the chest, e.g. for Hodgkin’s lymphoma
4. Dense breast tissue
: A recent study shows dense breast tissue (over 75% mammographic density) may increase a woman’s risk of breast cancer compared to women with less dense breast tissue.
Your breasts comprise a mix of fatty and dense breast tissue. Some women have a higher percentage of dense breast tissue which 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.
5. Your hormonal history
: Research is showing that there is a link between the length of time a woman is exposed to oestrogen and the development of a breast cancer. As a woman's ovaries produce oestrogen each month (except during pregnancy and breast feeding), exposure to oestrogen is increased by:
- Early age at first menstruation (under 12)
- Late age at first pregnancy (over 30)
- Having few or no pregnancies
- Limited or no period of breastfeeding
- Late age at menopause (over 55)
Furthermore, women who have their first child after 30 years of age have a long time before they have a break from oestrogen exposure - ‘oestrogen holiday'. Research shows that a possible contributing factor to the worldwide increase in breast cancer incidence over the last decade or so is women having their babies after 30 years of age. In previous decades, women were pregnant often at an earlier age, and had multiple births over several years (no ovulation so no oestrogen required). As a result, with the number of monthly cycles decreased, the length of time exposed to the hormone oestrogen was reduced - many ‘oestrogen holidays'.