Patients with total metabolic response on FDG-PET scan should get consideration with complete response. Those with a partial response on a CT scan and a complete metabolic response on FDG-PET scan should be considered to have achieved a low risk for melanoma relapse and complete response.

Patients with metastatic melanoma treated with anti-PD1 immune checkpoint inhibitors have experienced sustainable clinical activity. However, there’s the need to identify the strong predictive factors for relapse risk and long-term outcomes.

A study was conducted to compare FDG-PET imaging with CT scans to distinguish residual tumors and the absence of the tumor in metastatic melanoma patients treated with anti-PD1 immunotherapy. All patients considered to be in remission had FDG-PET imaging, and CT scans performed immediately after discontinuing immunotherapy treatment had clearly identified targets on the imaging scans.

The outcome of the first study was a relapse that occurred during follow-up. The CT imaging response was evaluated using criteria in solid tumors (RECIST): PR, progressive disease (PD), complete response (CR), and stable disease (SD). The FDG-PET imaging was classified as a progressive metabolic disease, stable metabolic disease, CMR, and residual FDG avidity (RFA).

In CT imaging, 9 out of 26 patients in complete remission had a CR, and 2 of them relapsed after 3 and 9 months; 15 of the participants had a PR and four relapses after 7, 13, and 14 months. Only two patients with an SD on CT scans did not relapse. There were no PDs either.

According to FDG-PET evaluations, 20 of the 26 patients in total remission had a CMR with only one relapsing after 9 months. Six participants had an RFA, with five of them relapsing after 3, 7, 13, and 14 months. None of the patients had a PMD or SMD.

There were discrepancies between PET and CT scans in 12 of the 26 patients. Ten of them showed a PR on the CT scan but a CMR on the FDG-PET scan, and none of them relapsed. The univariate analysis indicated that RFAs on FDG-PET scans were significantly linked to the occurrence of relapse. After making adjustments for age, sex, and RECIST score, FDG continued to be a good predictor of the relapse risk.

This model could help identify patients who are likely to respond to checkpoint inhibition in melanoma. The research team concluded that FDG-PET imaging can help predict long-term benefits of treatment and decision making regarding the discontinuation of treatment. More studies will be conducted to determine the stage of CR.