Aims: We investigate whether clinically applicable semi-quantitative parameters derived from hybrid FDG PET diagnostic contrast enhanced CT (FDG PET/CECT)can predict immunotherapy treatment response in non-small cell lung cancer (NSCLC) patients. The secondary aim was to assess the relationship of immune-related adverse events (irAEs) and metabolic activation of lymphoid cell-rich organs activation to response in patients continuing on immunotherapy.
Methods: Thirty-two patients who underwent hybrid FDG PET/CECT before and at first restaging after starting immunotherapy and with minimum 12 month 3 monthly FDG PET/CECT, were retrospectively analyzed. Imaging semi-quantitative parameters extracted were: SUVmax target lesion target lesion necrosis, SUVmax of dominant node and subsequently ΔSUVmaxTL ΔSUVmaxnode. These PET-derived parameters were correlated to responding or stable disease as assessed by both RECIST 1.1 and iRECIST 1.1. IrAEs, if present, were also described and correlated with clinical benefit as determined by continuation of therapy by the oncologist. SUVmax of the spleen and bone marrow (as indicators of activation of lymphoid cell-rich organs) at restaging scans were also correlated to clinical benefit.
Results: Of 32 eligible patients, 10 (31%) experienced iCPD, 8 (25%) showed iSD, 9 (28%) had iPR and 5 (16%) had iCR. ΔSUVmaxTL (p = 0.008) and ΔSUVmaxnode (p < 0.001) were significantly associated with iPD vs. non-iPD. The presence of irAEs or spleen/marrow activation were not correlated to response rates.
Conclusion: We describe semi-quantitative parameters on FDG PET/CECT by using the early interval metabolic delta and baseline necrosis as potential clinically useful and practical tools for iimmunotherapy treatment response evaluation in NSCLC. Metabolic activation of spleen/marrow from immunotherapy and irAEs in patients deriving continued clinical benefit were not significant factors influencing response.