Led by Professor Simon Lord, Department of Oncology, and funded by the World Cancer Research Fund, the study assessed real-world obesity rates in more than 79,000 patients across 13 cancer types. The findings demonstrate that relying on a single body mass index (BMI) measurement at treatment initiation substantially underestimates lifetime obesity exposure, with important implications for prognostication and personalised care.
Obesity is a well-recognised risk factor for numerous cancers, including breast, colorectal, and liver cancers, and has been linked to higher rates of surgical complications, untoward drug effects, and disease recurrence. With the rapid rise in obesity prevalence over the last three decades, clinicians are increasingly treating patients with obesity-related cancers, as well as patients with other cancers co-presenting with insulin resistance and metabolic dysfunction.
While the link between obesity and cancer development is well established, how obesity relates to cancer outcomes remains uncertain, with studies to date reporting mixed findings.
To address this, the research team analysed electronic health record data containing longitudinal BMI measurements for patients receiving first-line systemic therapy – treatments delivered via the bloodstream, such as chemotherapy – in England between 2013-2023. The calculated both obesity prevalence at treatment initiation and lifetime obesity prevalence, defined as any recorded BMI ≥30 kg/m².
Professor Simon Lord said:
“Cancer related weight loss and aging mean that lifetime exposure to obesity is often underestimated when using BMI at treatment initiation alone. This may be leading to inaccurate estimates of the impact of obesity on disease risk and prognosis. By examining obesity history alongside BMI at the start of treatment, we aimed to provide a more accurate picture of pre-diagnostic exposure.”
At the start of treatment, 26.4% of patients were classified as obese. However, lifetime obesity prevalence was more than double, at 53.5% across all cancer types. On average, lifetime prevalence was 28.3 percentage points higher than prevalence at treatment initiation, ranging from a 19.1 percentage point increase in breast cancer to a 43.0 percentage point increase in pancreatic cancer.
© Perletta, et al. 2026. Reproduced from ESMO Real World Data and Digital Oncology, [Real-world obesity prevalence and history in 79 271 patients receiving systemic anticancer therapy across 13 cancer types in England (2013-2023)], CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/).
Dr Victoria Perletta, Senior Research Fellow at the Department of Oncology and study author, said:
“Across our large, real-world cohort, approximately one in four cancer patients in England were living with obesity at the start of systemic treatment, while half had a history of obesity. This is the first study to quantify the vast underestimation of lifetime obesity exposure when relying on BMI at first systemic therapy, highlighting the importance of considering both measures. Our findings suggest significant implications for understanding the relationship between obesity and cancer outcomes, particularly in the context of precision medicine”.
Professor Lord added:
“How obesity affects cancer prognosis is extremely complex, with both current and previous obesity likely to be important. Patients can lose weight as a result of cancer, however, the consequences of obesity, including metabolic dysfunction, inflammation and insulin resistance, may well be sustained and these factors may influence the effectiveness of cancer treatments and in turn, cancer outcomes. Not considering both these measures in clinical decision making and outcomes research risks missing an important part of the picture.”
The results also provide important information about the prevalence of obesity in a real-world cancer population, which is relevant for healthcare planning, given the role of body weight in treatment decisions such as chemotherapy dosing. The authors note that these questions may become increasingly important with the growing use of weight-loss therapies, including GLP-1 and dual GIP/GLP-1 receptor agonists.
This study highlights the value of using longitudinal BMI measures to accurately classify obesity exposure in cancer patients. Further research is needed to examine how factors such as maximum lifetime BMI, as well as the timing and duration of obesity, influence cancer outcomes.
World Cancer Research Fund’s International Assistant Director of Research and Policy, Dr Helen Croker, said:
“This research highlights the opportunity to consider patients’ history of obesity alongside their current health when thinking about broader clinical decision-making. Our previous research highlighted how a lack of accurate pre-diagnosis body weight measures in studies of people living with and beyond cancer presented limitations for interpreting the role of BMI on outcomes. It is wonderful to see research we have funded addressing key questions where we have been missing data.”
‘Real-world obesity prevalence and history in 79,271 patients receiving systemic anticancer therapy across 13 cancer types in England (2013–2023)’ was published in ESMO Real World Data and Digital Oncology on 24th April 2026.