'Women who are obese and develop breast cancer are 41 per cent more likely to die earlier than women who are in the normal weight range before diagnosis.'
This is one of the findings of a paper published this week in the respected Annals of Oncology journal and written by a team of scientists involved in World Cancer Research Fund's Continuous Update Project (CUP).
Typically, this kind of finding would make the pages of a national newspaper or two, where it would inspire fevered debate about the consequences of becoming overweight or how we should all be using the gym.
However, this research is exploring a new area when it comes to cancer prevention - namely, what people who have already had cancer can do to prevent its recurrence or risk of other diseases. World Cancer Research Fund's work looks at how to prevent cancer in the first place and as we broaden our research to examine issues such as the relationship between body weight and cancer among cancer survivors, we enter an even more complex field with many more factors to account for. This means adopting an extremely cautious approach when it comes to interpreting the scientific evidence.
World Cancer Research Fund's CUP panel of expert scientists will consider this evidence and its implications before we issue a formal report in the autumn that will also cover other factors that affect cancer risk such as physical activity and diet. It is only at this stage that we will assess if the evidence is robust enough to confidently provide breast cancer survivors with any clear health recommendations.
Showing the way
This paper, authored primarily by a team from Imperial College London, is a great pointer to where further studies should look and what other factors need to be taken into consideration as different types of research test the paper's conclusions.
These conclusions - that being obese or overweight is associated with poorer survival rates among breast cancer patients and that trials are needed to test if women who achieve and maintain a healthy weight have improved survival rates after breast cancer diagnosis - are an important development in this new area of research.
About the research
The paper, Body mass index and survival in women with breast cancer - systematic literature review and meta-analysis of 82 follow-up studies, is a systematic literature review of 82 cohort studies that included more than 213,000 breast cancer survivors, of whom nearly 41,500 died from various diseases during the studies, not just cancer.
This kind of research can provide strong evidence that something is going on and raises questions that need to be investigated further. So while the research suggests a link between being obese and higher mortality rates for breast cancer survivors, important factors such as the presence of other diseases, types of treatment experienced or the impact of intentional weight loss were not accounted for in most of the studies analysed.
Better-designed studies could provide higher quality information on the impact of weight gain at various stages in life and after diagnosis. Randomised controlled trials are also needed to identify if losing weight leads to better survival rates among women with breast cancer.
Promoting research that is not fully developed in terms of how it would apply to people in the real world can devalue scientific endeavour in the eyes of the public - leading to the cry that "scientists are always changing their minds so I'm just going to ignore them".
This is dangerous because people then ignore the good advice as well as the not-so-good advice.
This research, however, is still a crucial early step on the road to improving our understanding of the impact of body weight on breast cancer survivorship.
Ultimately, World Cancer Research Fund wants to add to the cancer prevention advice we provide to the general population with specific recommendations for people who have survived the most common forms of cancer. The completion and publication of this piece of research is a vital building block in that process.