Weight loss jabs could make cancer scans less effective, study suggests

Weight loss jabs such as Mounjaro and Wegovy could make some cancer scans less effective, leading to unnecessary tests and possible delays in treatment, experts suggest.

The drugs, collectively known as GLP-1s, have helped millions lose up to a fifth of their body weight but may alter how tissue appears on PET-CT scans used to diagnose and stage cancers.

The changes could cause healthy tissue to be misinterpreted as potentially cancerous, meaning some patients may face extra investigations and anxiety while awaiting results.

British researchers at Alliance Medical, a leading provider of diagnostic imaging in the UK, identified the issue after noticing unusual patterns in patient scans.

PET-CT scans combine CT and PET imaging, using a mildly radioactive liquid called a tracer to highlight areas where cells are more active than normal. Brighter spots can indicate cancer, though they may also reflect infections or inflammation.

“We noticed unusual uptake in one of our patients on a GLP-1 agonist, which prompted a wider review across our network,” said Dr Peter Strouhal, medical director at Alliance Medical and lead author of the study.

“We found that these altered patterns are increasingly common, yet there is currently no national or international guidance in the UK addressing this emerging issue.”

The review of several PET-CT scans found atypical tracer patterns among GLP-1 users that “could be misinterpreted” as hot spots or potentially cancerous areas.

“Recognising the characteristic uptake associated with GLP-1 agonists helps avoid unnecessary anxiety and interventions, ensuring patients receive the right care, at the right time, without detours or doubt,” Dr Strouhal said.

Researchers said larger studies involving more data are needed before recommendations can be made to change PET-CT scan guidelines for weight loss jab users.

They advised clinicians to consider a patient’s medical history when interpreting results.

It follows earlier US research suggesting GLP-1 drugs could interfere with breast-cancer chemotherapy medicines.

That study tracked hundreds of women with early-stage triple-negative breast cancer during and after treatment.

Twenty-five were already taking GLP-1s alongside other diabetes drugs and continued doing so while undergoing chemotherapy.

Two years later, 28 per cent of the women on GLP-1s had fully responded to treatment and were clear of cancer, compared with 63 per cent of those not using the drugs.

Researchers also found GLP-1s had entered tumour and immune cells in tissue samples from the patients.

“Use of GLP-1 use may need to be carefully considered during breast cancer therapy,” said Dr Bethania Santos, oncologist and researcher at UT Southwestern Medical Center in Dallas, who presented the study at the San Antonio Breast Cancer Symposium.

However, experts at the time said the drugs themselves may not have reduced the effectiveness of chemotherapy.

People with advanced diabetes who require several medicines already have a higher risk of breast-cancer recurrence.

The study did not prove whether weight-loss drugs help or hinder the success of cancer therapy.