Over 13,500 women are diagnosed with breast cancer in Australia each year. After completing initial treatment, the immediate question for many, if not most, is – what are the chances my cancer will return?

A major source of anxiety is the fear the cancer will not only return, but spread to other areas of the body. Such cancer spread is known as advanced or “metastatic” breast cancer.

Doctors often use information from breast cancer clinical trials when trying to answer this question. But trials, although very valuable, often select out women with certain characteristics and sometimes exclude older women, so it’s difficult to know how closely their results represent “real world” experiences.

We have just completed the first Australian study, published in the Medical Journal of Australia, to try to better answer the question of recurrence risk. Our aim was to report the average risk of metastatic breast cancer occurring within five years of a diagnosis for women who don’t have distant spread at their initial diagnosis. To do this, we used de-identified data collected from all women diagnosed with breast cancer across New South Wales in 2001 and 2002.

The research included 6,644 women who fit our set parameters. Overall, we found that one in ten subsequently had metastatic breast cancer (recorded by hospitals or the NSW cancer registry) within five years. When we examined only women who had breast cancer localised to the breast (with no spread to lymph nodes under the arm) we found the risk was much lower – one in 20. For women who had breast cancer with spread to the lymph nodes or large breast cancers that involved the skin, the risk was 18%.

Our findings are average estimates. For individual women in all these groups, the risk of cancer spread will depend a number of factors, including the biological features of her cancer (breast cancer can be subdivided into different cancers, each with its own distinct biological features) and the type of treatment received (for example, whether she received chemotherapy or hormonal treatment after surgery, which is known as adjuvant therapy). Many women will have lower risks than our averages.

This study provides the first available Australian information about risk of distant cancer spread drawn from the general breast cancer population. What we’ve found can be used as a starting point for discussions between women and their doctors about the chance of cancer spread.