PET/CT at 1 Week May Predict Melanoma Patients’ Response to Pembrolizumab

Findings on PET/CT conducted 1 week after the start of pembrolizumab may predict outcomes of the treatment in patients with advanced melanoma, according to a study published in Clinical Cancer Research.

Researchers found that metabolic flare or metabolic response, visualized with FDG PET/CT about 1 week after the start of pembrolizumab treatment, is associated with a higher rate of clinical response and longer progression-free survival (PFS).

This prospective study (ClinicalTrials.gov Identifier: NCT02791594) included 19 patients with advanced melanoma. At baseline, their median age was 71 (range, 24-89) years, 74% of patients were men, and 11% had liver metastases. Most patients (84%) had not received prior treatment, but 1 patient each had received ipilimumab, targeted therapy, and radiotherapy to the brain.

The patients underwent FDG PET/CT at a median of 9 (range, 0-24) days before starting pembrolizumab and at a median of 7 (range, 3-21) days after the first pembrolizumab dose. The researchers evaluated scans for changes in maximum standardized uptake (SUV_max).

The second scan revealed a metabolic flare or metabolic response in 6 patients and stable metabolism in 13 patients. Metabolic flare was defined as having an increase in tumor SUV_max of more than 70%, and metabolic response was defined as a decrease in tumor SUV_max of more than 30%. Patients without a metabolic flare or response were considered to have stable metabolism.

The objective response rate was 58% in the overall cohort, 100% in patients with a metabolic flare or metabolic response, and 38% in patients with stable metabolism (P =.018).

At a median follow-up of 38 months, the median PFS was not reached in patients with a metabolic flare or metabolic response and was 2.8 months in patients with stable metabolism (P =.017).

The 3-year overall survival (OS) rate was 83% in patients with a metabolic flare or metabolic response and 62% in patients with stable metabolism. The median OS was not reached in either group (P =.330).

“Early FDG PET/CT can identify metabolic changes in melanoma metastases that are potentially predictive of response to pembrolizumab and significantly correlated with PFS,” the researchers concluded. “Given that FDG PET/CT is ubiquitous and routinely used to image patients with cancer, and changes in tumor SUV_max can be easily calculated, this approach has the potential to be readily applied to clinical practice.”

Disclosures: This research was supported by Merck Sharp & Dohme LLC. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

This article originally appeared on Cancer Therapy Advisor