18FDG PET/CT in the early assessment of non-small cell lung cancer response to immunotherapy: frequency and clinical significance of atypical evolutive patterns

PURPOSE

This prospective study aimed (1) to assess the non-small cell lung cancer (NSCLC) evolutive patterns to immunotherapy using FDG-PET and (2) to describe their association with clinical outcome.

DESIGN

Fifty patients with metastatic NSCLC were included before pembrolizumab or nivolumab initiation. FDG-PET scan was performed at baseline and after 7 weeks of treatment (PET_interim1) and different criteria/parameters of tumor response were assessed, including PET response criteria in solid tumors (PERCIST). If a first PERCIST progressive disease (PD) without clinical worsening was observed, treatment was continued and a subsequent FDG-PET (PET_interim2) was performed at 3 months of treatment. Pseudo-progression (PsPD) was defined as a PERCIST response/stability on PET_interim2 after an initial PD. If a second PERCIST PD was assessed on PET_interim2, a homogeneous progression of lesions (termed immune homogeneous progressive-disease: iPD_homogeneous) was distinguished from a heterogeneous evolution (termed immune dissociated-response: iDR). A durable clinical benefit (DCB) of immunotherapy was defined as treatment continuation over a 6-month period. The association between PET evolutive profiles and DCB was assessed.

RESULTS

Using PERCIST on PET_interim1, 42% (21/50) of patients showed a response or stable disease, most of them (18/21) reached a DCB. In contrast, 58% (29/50) showed a PD, but more than one-third (11/29) were misclassified as they finally reached a DCB. No standard PET_interim1 criteria could accurately distinguished responding from non-responding patients. Treatment was continued in 19/29 of patients with a first PERCIST PD; the subsequent PET_interim2 demonstrated iPD_homogeneous, iDR and PsPD in 42% (8/19), 26% (5/19), and 32% (6/19), respectively. Whereas no patients with iPD_homogeneous experienced a DCB, all patients with iDR and PsPD reached a clinical benefit to immunotherapy.

CONCLUSION

In patients with a first PD on PERCIST and treatment continuation, a subsequent PET identifies more than half of them with iDR and PsPD, both patterns being strongly associated with a clinical benefit of immunotherapy.

18F-FDOPA PET for the diagnosis of parkinsonian syndromes

18F-FDOPA PET has been historically used for the evaluation of parkinsonian syndromes in research settings. With the wider availability of PET cameras and 18F-DOPA this method can be used as a clinical diagnostic tool. Current acquisition protocols are simple with a 10 minute static acquisition performed 90 minutes post injection. Criteria for precise visual analysis of the images are defined. The performances of the method are reviewed throughout the literature. The method is very sensitive for detection of IPD versus normal patients. Few studies comparing 18F-FDOPA PET and DAT SPECT did not show any difference in diagnostic accuracy. 18F-FDOPA PET is reliable for evaluation of IPD progression. In general, atypical Parkinson's syndromes cannot be reliably differentiated from IPD since they share a similar nigro-striatal degeneration process. However, some patterns such as the asymmetrical faint homogeneous striatal uptake reduction pattern of CBD can be recognized. The short acquisition protocol, the various indications in oncology of 18F-FDOPA and the high quality of PET images are in favor of this technique in daily clinical practice for the improvement of diagnosis of parkinsonian syndromes.