PEOPLE WITH MELANOMA who receive immunotherapy typically undergo an 18F-fluorodeoxyglucose (FDG) PET/CT scan about three months after starting treatment to see whether their tumors are responding. A study published May 1, 2024, in Clinical Cancer Research has found FDG PET/CT—one of the most readily available ways to detect cancer—can reveal responses to immunotherapy just one week after people with metastatic melanoma begin treatment.

“It was extremely exciting to see these very large changes in FDG activity, which were only seen in responding patients and were correlated with progression-free survival,” says study author Michael D. Farwell, a radiologist at the Hospital of the University of Pennsylvania in Philadelphia.

The study enrolled 19 people with metastatic melanoma who were scheduled to receive the immunotherapy drug Keytruda (pembrolizumab). Patients had FDG PET/CT scans prior to starting therapy and one week after starting treatment to identify any changes in tumor metabolism. Eleven of the 19 participants had tumors that responded to therapy.

The scan detected increased metabolism, due to increased levels of immune cells in the tumors, or decreased metabolic activity, due to tumor cell death, in six of 11 patients who responded to Keytruda. The scan did not detect metabolic changes in any of the eight patients whose cancer didn’t respond to Keytruda.

Median progression-free survival was more than three years in the group with metabolic changes compared with less than three months in patients who had no detectable metabolic changes. “Biomarkers of response to immunotherapy need to not just predict response but to also correlate with survival, so it was also exciting to see that there was a correlation between these large metabolic changes and survival,” says Farwell, who notes that this approach could help physicians assess response to immunotherapy earlier to potentially consider other options in those who are not responding.

Farwell and his colleagues now plan to validate the results in another clinical trial with more people with melanoma, who will receive one of two current standard-of-care combination immunotherapies for melanoma—either Opdualag (nivolumab plus relatlimab) or Opdivo (nivolumab) plus Yervoy (ipilimumab).