Risk factors

Breast cancer is the most common cancer to affect women.

There is an increasing incidence worldwide with over one million new cases diagnosed each year.

In the USA, an estimated 212,000 new cases of invasive breast cancer are expected to be diagnosed each year, along with 61,000 new cases of non-invasive breast cancer. Almost 41,000 women are expected to die annually from this disease.

In the UK there are approximately 35,000 new breast cancers diagnosed and 14 500 deaths due to breast cancer each year.

In New Zealand approximately 2400 new cases are diagnosed each year and 600 women die from this disease.

Breast cancer rates vary dramatically in different countries and societies. The rate is highest in developed industrialised nations such as the USA ( 98 per 100000 ) and Australia and New Zealand are not far behind. Countries in Eastern Asia have rates of less than 40 per 100000.

View Interactive World Map of Breast Cancer Rates - Time Magazine

Equally interesting is the fact that women who migrate to live in a high risk country aquire the higher risk rate within a few years. This data would suggest that the incidence of breast cancer has much to do with environmental and lifestyle factors.

A number of factors have been associated with an increased risk of breast cancer

What are the risk factors?

Age: Risk increases with age. More than 50% of new cases occur in women more than 50 years old.

Sex: Breast cancer mostly affects women, however 1% of breast cancer occurs in men.

Family history: 5 - 10% of patients have a family history of breast cancer.

Genetic: Some families have inherited genetic abnormalities that increase their risk of breast cancer. The most wellknown are BRCA 1 and BRCA 2 gene abnormalities. Genetic changes are only identified in < 5 % of cases. Read more

Hormonal factors: Being exposed to cyclical fluctuations of oestrogen for long periods of time increases risk; therefore early menstruation and late menopause both increase risk.

Early pregnancy is protective

Breastfeeding is protective.

Hormone replacement therapy: The latest information is from the Women's Health Initiative study. The WHI was run by the National Institute of Health in the USA and was launched in 1991. It consisted of a set of clinical trials and an observational study, which together involved 161,808 healthy postmenopausal women. The trials were designed to test the effects of postmenopausal hormone therapy, diet modification, and calcium and vitamin D supplements on heart disease, fractures, and breast and colorectal cancer.

The hormone component of the trial had two studies: the oestrogen-plus-progestin study of women with a uterus involved 16,608 women and the oestrogen-alone study of women without a uterus which involved 10,739 women. These studies were both ended prematurely when data showed adverse side effects in those being treated with hormones. The women in these studies are now participating in a follow-up phase, which will last until 2010.

Amonst other effects this study showed an increase in breast cancer risk with oestrogen plus progestin use. (38 cases per 10000 vs 30 cases per 10000 women). This finding has been confirmed in another large English trial called the Million Women study.

The New Zealand Guidelines Group produced a set of recommendations for HRT use based on the WHI report in 2004. www.nzgg.org.nz

Obesity  - increases risk of post-menopausal breast cancer.

Exercise  - regular exercise reduces risk of breast cancer.

Alcohol  - more than 1 standard drink per day increases risk of breast cancer. One or two drinks per day resulted in a 10% increase, more  than three drinks daily up to 30% increase.

Diet  - Diet is extremely important for general good health and poor diet and has been associated with an increased risk of a number of common cancers including breast and bowel.

In reality most women who develop breast cancer do not have any obvious increased risk factors. Therefore every woman should seek prompt and thorough assessment of any breast changes that are noticed!

NBCC Risk Calculator

How can you modify your risk?