Weight Loss Injections May Compromise Cancer Scan Accuracy

Recent research indicates that weight loss injections, specifically glucagon-like peptide-1 receptor agonists (GLP-1s), could significantly impact the reliability of cancer scans. These findings raise concerns about the potential for misdiagnosis in patients undergoing treatment with these medications.

The study, led by Dr. Peter Strouhal, medical director at Alliance Medical in the UK, revealed that commonly used weight loss drugs such as Mounjaro and Wegovy may alter how tissues appear on PET-CT scans. These scans, essential for diagnosing and staging cancer, use a mildly radioactive tracer to identify areas of increased metabolic activity, which can indicate cancerous growths.

Researchers found that patients using GLP-1s exhibited atypical patterns on their scans, which could be misinterpreted as potential cancer hotspots. This misinterpretation may lead to unnecessary follow-up tests, causing undue stress and delays in appropriate treatments.

In their investigation, the research team reviewed multiple PET-CT scans of patients on GLP-1s after noticing an anomaly in one patient’s results. The altered tracer patterns were identified as increasingly common among users of these weight loss injections, prompting the need for further examination and potential updates to scanning guidelines.

Dr. Strouhal emphasized the importance of recognizing these patterns to prevent unnecessary anxiety for patients. “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,” he stated.

The research is set to be presented on October 8, 2025, at the Annual Congress of the European Association of Nuclear Medicine in Barcelona. Further studies are essential to substantiate these findings and determine if changes to PET-CT scan protocols are warranted for all patients using weight loss injections.

This study follows previous concerns raised about GLP-1 drugs potentially interfering with breast cancer chemotherapy. A separate investigation conducted in the United States tracked women with early-stage triple-negative breast cancer who were already taking GLP-1s alongside other diabetes medications during their treatment. The results suggested that only 28 percent of the women on GLP-1s achieved a complete response to their cancer therapies, compared to 63 percent of those who were not on these medications.

Dr. Bethania Santos, an oncologist at UT Southwestern Medical Center in Dallas, presented findings at the San Antonio Breast Cancer Symposium, indicating that while the drugs may not directly diminish chemotherapy effectiveness, those with advanced diabetes may be at a greater risk for cancer recurrence.

While the current research highlights significant concerns regarding the impact of GLP-1s on both cancer diagnosis and treatment, medical professionals urge that careful consideration of a patient’s medical history be paramount when interpreting scan results. Continued investigation will be vital to ensure that patients on these medications receive accurate assessments and appropriate care.