How likely is my breast cancer to recur and spread?

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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 today 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 6644 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.

Up until now, we only had information about average survival rates because these data are routinely reported by cancer registries. But there was no general information about how commonly cancers recur. And health-care providers didn't have information about how many women with breast cancer would be affected by metastatic breast cancer.

There have been major changes in the management of breast cancer over the last 20 years based on the results of clinical trials, including the introduction of treatments that target specific biological types of breast cancers, such as tamoxifen, an anti-oestrogen treatment (for women with breast cancers classified as "oestrogen receptor positive"). And we've known that average survival rates for women with breast cancer have been improving since the mid-1990s.

But oddly, we've had no information about the impact of these advances on a woman's risk of distant spread, which is the question of most immediate concern to women after their initial treatment. Breast cancer consumer groups have made it clear that women want reliable and up-to-date information about this risk.

Our research provides important information about the pattern of risk over the first five years after initial treatment. We've known from clinical trials that a woman's annual risk of distant spread peaks in the second year after diagnosis. Our study confirms this is also the case for the general breast cancer population, including women in different age groups.

We found that despite recent treatment advances, women with breast cancer spread to the lymph nodes at diagnosis are still at higher risk of distant spread, as are women younger than 50 years at initial diagnosis, who are known to have more aggressive cancers. Less easy to explain is the fact that women living in areas of socioeconomic disadvantage had a higher risk of distant spread but the finding is consistent with Australian evidence of reduced breast cancer survival among women living in disadvantaged areas.

Our research was limited by the fact that we didn't have access to medical records, so we could only identify cases of metastatic cancer that were recorded on hospital records or the cancer registry. We couldn't include women with distant spread who didn't require hospital care or pathology tests that would be notified to the cancer registry - so there's a chance that we may have underestimated the average five-year risks. This limitation can only be addressed if cancer registries start routinely collecting and reporting information about all new cases of distant spread.

Mandatory reporting of metastatic breast cancer has been recently introduced in the United Kingdom. And routine reporting is on the agenda of cancer agencies in Australia, in large part due to strong advocacy from breast cancer consumer groups who are seeking answers to the questions that matter most to women with breast cancer. Here's to hoping Australian registries follow suit.

This article was first published in The Conversation