11: Correlation of PSMA expression on [18F]PSMA-1007 PET with morphological changes in patients with metastatic renal cell cancer undergoing tyrosine kinase and checkpoint inhibitor therapy
student Department of Nuclear Medicine, University Hospital, LMU Munich, Munich, Germany, Germany
Background: The introduction of tyrosine kinase (TKI) and checkpoint inhibitors (CI) prolonged overall survival in patients with metastatic renal cell carcinoma (mRCC). The image-based evaluation of treatment response is essential in clinical practice, as serum biochemistry markers are unavailable in RCC. PSMA is reportedly expressed by RCC lesions. We sought to compare morphological and functional response on [¹⁸F]PSMA-1007 PET in mRCC treated with TKI / CI therapy.
Methods: Patients with mRCC undergoing [¹⁸F]PSMA-1007 PET/CT prior and eight weeks after initiation of therapy (TKI/CI) were included. Treatment response was evaluated on PET and CT separately. Changes on PET were determined using a modified PERCIST score (mPERCIST) and the whole tumor volume (WTV). CT response was evaluated according to RECIST 1.1 criteria. Results of response assessment in both imaging modalities were compared.
Results: 25 patients with mRCC were included. PERCIST evaluation on follow up classified as follows: 6 patients with complete response (24%), 4 with partial response (16%), 6 with stable disease (24%) and 8 (32%) with progressive disease. Using RECIST 1.1 criteria, 2 patients showed partial response (8%), 15 stable disease (60%) and 6 progressive disease (24%), 1 had no evaluable lesions (4%). One patient was lost to follow-up. Concordant classifications were found in 11 cases (44%). Changes in WTV were significantly correlated with changes in SUVmax (r=0.882; r2=0.779; p< 0.001) and SUVmean (r=0.734; r2=0.539; p< 0.001). Changes in the RECIST defined target sum were not significantly correlated with changes in PET, e.g. WTV (r=0.056; r2=0.003; p=0.814), SUVmax (r=-0.097; r2=0.009; p=0.683), SUVmean (r=-0.073; r2=0.005; p=0.761).
Conclusions: Changes in PSMA expression were not correlated with response on RECIST 1.1; thus, PSMA expression might serve as biomarker beyond CT-related changes. Furthermore, PET might be used as an predictor of overall survival in patients with mRCC.