Programmed death ligand-1 PET imaging in patients with melanoma: a pilot study

Programmed death ligand-1 (PD-L1) is an inducible protein heterogeneously expressed in melanoma. Assessment of PD-L1 expression is challenging and standard immunohistochemistry (IHC) requires biopsies and cannot capture heterogeneity of expression. Noninvasive imaging methods provide evaluation of expression across lesions in the body. We conducted a prospective pilot trial with PD-L1 PET imaging with [ 18 F]-BMS-986229 as a noninvasive approach to assess PD-L1 expression across lesions, in 10 patients with advanced melanoma, longitudinally during treatment with nivolumab and ipilimumab. PET imaging was performed at baseline and at 6 weeks after initiation of treatment. We examined the relationship of PD-L1 PET uptake to radiographic clinical response. [ 18 F]-BMS-986229 uptake was variably seen across lesions in patients at baseline. All patients showed positive uptake in lesions at baseline PET with a median SUV max of 3.6 (range: 1.7-8.6). PD-L1 PET SUV max decreased in all but two lesions 6 weeks after treatment initiation. Four of five patients had a mean (SUV max ) greater than or equal to 3.00 in Response Evaluation Criteria in Solid Tumors (RECIST) evaluable lesions at baseline, and all had a RECIST response while all progressors ( n  = 3) had baseline PD-L1 mean SUV max less than or equal to 2.60. A higher lesional baseline SUV max was associated with greater individual lesion reduction during treatment. The PD-L1 uptake in lesions showed a low correlation with baseline PD-L1 by IHC. In this small pilot study, PD-L1 PET imaging using [ 18 F]-BMS-986229 showed feasibility in noninvasively assessing lesion uptake and PD-L1 heterogeneity in patients receiving combination immunotherapy. Future exploration of this tracer in larger patient cohorts is necessary to delineate its use in managing immunotherapy treatments.