Weight-loss drugs offer a new weapon in the global fight against cancer, with “enormous potential” to prevent new cases and shrink tumours, doctors said as research showed the jabs can cut the risk of developing the disease by a fifth. Blockbuster injections such as Wegovy have revolutionised the treatment of obesity, and recently been approved for use in other areas of medicine, including reducing the risk of heart attacks, strokes and cardiovascular-related deaths. Now experts say they increasingly believe weight-loss drugs could play a big role in preventing and treating cancer, the second leading cause of deaths globally. A study presented at the world’s largest cancer conference found patients taking the drugs were 19% less likely to develop 13 obesity-related cancers, including ovarian, liver, colorectal, pancreatic, bowel and breast cancer. The research involving 34,000 people, led by the Case Western Reserve University in Ohio, also found patients were half as likely to die over 15 years compared with patients not taking the jabs, also known as GLP-1 receptor agonists (RA). The study co-authors, Dr Cindy Lin and Dr Benjamin Liu, said: “Our findings are significant in that they could change the paradigm of obesity management by suggesting early intervention with GLP-1 RAs could delay or prevent obesity-related cancer development.” There could be “multiple” ways in which the drugs cut the risk of cancer – not just by helping people to lose weight, they added. A second study published at the American Society of Clinical Oncology (ASCO) annual meeting suggested weight-loss drugs could reduce the risk of cancer coming back in breast cancer patients – and boost their prospects of long-term survival. Researchers from Memorial Sloan Kettering Cancer Centre in New York said the jabs could cut the risk of cancer recurrence and be a “new tool” against the disease. A third paper released at ASCO and led by Yale University, also looking at breast cancer patients, suggested taking weight-loss drugs reduced the chances of the disease returning. Speaking in Chicago at ASCO, Dr Mitchell Lazar, the director of the institute for diabetes, obesity and metabolism at the University of Pennsylvania School of Medicine, said: “GLP-1 based therapies are highly effective at producing weight loss, and thus one of the fundamental mechanisms by which they improve cancer outcomes is via the impressive weight loss that they produce. “Obesity is a risk factor for nearly all cancers, in both men and women. Thus the revolution in the medical treatment of obesity has enormous potential to prevent new cancers, reduce the severity and growth rate of existing tumours, and synergise with new cancer-specific therapies.” Dr Jennifer Ligibel, a senior physician at Dana-Farber Cancer Institute who was not involved with the studies, said: “These are exciting, preliminary findings of a link between use of GLP-1 RAs and cancer risk.” They added to previous work suggesting the drugs could reduce cancer risk, she added. A study published last December showed they were associated with a 50% reduced risk of bowel cancer in people with type 2 diabetes. “Individuals with diabetes who were prescribed a GLP-1 RA had a lower risk of colorectal cancer as compared with individuals who were not prescribed one of these drugs,” Ligibel said. Dr Julie Gralow, the chief medical officer of ASCO, said the evidence was not clear yet as to whether the potential benefits of weight-loss drugs in reducing cancer risk were just as a result of weight loss – or whether there were other, unknown factors at play. Gralow, a world-renowned cancer expert who was named woman oncologist of the year in 2023, said she was absolutely certain the jabs would become a much greater focus of cancer prevention research in the future. “The more we can do to reduce the risk factors and prevent cancer, the better,” she added. “I do think that there are so many potential and already proven health benefits to these drugs, that it would be icing on the cake if we saw that they were also reducing cancers. “I am very hopeful about overall improvements in health from this class of drugs.” Cancer Research UK’s chief clinician, Prof Charles Swanton, cautioned it was still “early days”. There have been suggestions the drugs could even raise the risk of certain cancers, although recent research on thyroid cancer and pancreatic cancer has cast doubt on those concerns. “Well-designed prospective trials with randomised data will provide more clarity on the potential and safety of weight-loss drugs to lower people’s risk of cancer,” said Swanton.