A landmark study has revealed that more than half of cancer patients starting treatment in England have a history of obesity. The stark role obesity plays in the deadly disease is even greater than feared, with previous estimates suggesting it could be fueling four in ten cases.
Study Findings
Experts from the University of Oxford found that relying on a single weight measurement when treatment begins may greatly underestimate a patient's lifetime obesity, which can change their chance of survival. Obesity has been linked to at least 13 types of cancer, but experts have now warned that losing weight is not enough.
Dr Helen Crocker from the World Cancer Research Fund said: 'This research highlights the opportunity to consider patients’ history of obesity alongside their current health when thinking about broader clinical decision-making. Although the link between obesity and cancer risk is well established, its impact on cancer outcomes remains uncertain and relying only on BMI at treatment start may miss important lifetime exposure that could influence cancer prognosis.'
The study, which spanned over a decade, found that when past obesity was included, prevalence exceeded 50 per cent in every one of the 13 cancers studied. When just one BMI measurement was used, just 25 per cent of patients were classed clinically obese.
Pancreatic Cancer Example
For pancreatic cancer, whilst only 14 per cent of patients were obese at the start of treatment, 56 per cent were obese at some point in their lifetime, demonstrating that current weight doesn't provide a full picture of someone's health.
The findings, published in the journal ESMO Real World Data and Digital Oncology, highlight the need to tackle obesity head on, rather than treat it later down the line, experts said.
Research Methodology
The team, led by Professor Simon Lord, an expert in cancer treatment, found that previous excess weight can significantly influence treatment success. They analysed past BMI data from digital health records of 79,271 patients who were receiving systemic treatments, which includes any kind of therapy where drugs travel through the bloodstream, like chemotherapy.
Results showed that obesity rates vary across cancer types, with those that commonly present as unexplained weight loss and lack of appetite linked with lower obesity rates at first treatment. These included pancreatic, gastroesophageal, bowel and lung cancer, as well as non-Hodgkin lymphoma, which affects infection-fighting white blood cells.
Obesity was more common at treatment start for uterine, breast cancer and malignant melanoma, a type of skin cancer that can spread to other areas of the body.
Further analysis showed that older patients, aged 75 and older when they started treatment, had lower obesity rates, whilst those living in more deprived areas were more likely to be obese.
Biological Mechanisms
Scientists believe obesity may increase cancer risks through biological mechanisms such as chronic inflammation, alterations in metabolism, and changes in hormone levels. Reduced participation in cancer screening programs and decreased efficacy of screening procedures, which is more common in areas of deprivation, in people living with obesity may also be factors.
The researchers concluded: 'Our findings suggests significant implications for understanding the relationship between obesity and cancer outcomes, especially for precision medicine. This study provides clear rationale for considering both current and past BMI in clinical decision making and outcomes research. Not doing so risks missing an important part of the clinical picture.'
Dr Victoria Perletta, senior research fellow at the university's oncology department, added: 'Our work could have implications for clinical decision-making, as understanding a patient’s history of obesity may help build a fuller picture of their health than BMI at treatment start alone. Because body weight can inform chemotherapy dosing, this may also be relevant to more personalised care.'
Future Implications
The experts stressed that the growing use of now household weight loss jabs such as Wegovy and Mounjaro may further change obesity patterns in cancer patients, making tracking weight over time more important than ever.
'A future challenge in understanding this complex relationship will be the increasing availability and exposure of patients to GLP-1s and other treatments in development for use in diabetes and weight loss, and arguably, longitudinal BMI measures will become even more important,' they said. 'Time will show if expanded GLP-1 use reduces obesity in patients receiving systemic anticancer therapy; we will understand the benefits and risks of these drugs used in conjunction with systemic therapy and determine whether GLP-1 receptor agonists positively impact upon cancer outcomes.'
Health charities have welcomed the findings, labelling the research timely in a population very minimally exposed to weight loss interventions. Dr Crocker said: '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.'
Cancers Linked to Obesity
The International Agency for Research on Cancer identified 13 types of cancer with an obesity link in 2016. These included breast, bowel, womb, kidney, pancreatic, oesophageal, gallbladder, liver, upper smooch, myeloma, meningioma (a type of brain tumour), and thyroid cancer. This does not mean that everybody who is overweight or has a history of obesity will develop cancer.
In 2024, experts from Lund University, Sweden, identified a further 19 types of cancer that appear to be linked to excess weight, adding gastric tumours, cancers of the small intestine and pituitary glands as well as types of head and neck cancer, vulval and penis cancer to the list.
