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Introduction: Therapeutic options in advanced medullary thyroid carcinoma (MTC) have markedly improved since the introduction of tyrosine kinase inhibitors (TKI). We
aimed to assess the role of metabolic imaging using 2-deoxy-2-(\(^{18}\)F)fluoro-D-glucose (\(^{18}\)F-FDG) positron emission tomography/computed tomography (PET/CT) shortly before and 3 months after initiation of TKI treatment.
Methods: Eighteen patients with advanced and progressive MTC scheduled for vandetanib treatment underwent baseline \(^{18}\)F-FDG PET/CT prior to and 3 months after TKI treatment initiation. During follow-up, CT scans were performed every 3 months and analyzed according to Response Evaluation Criteria In Solid Tumors (RECIST). The predictive value for estimating progression-free (PFS) and overall survival (OS) was examined by investigating \(^{18}\)F-FDG mean/maximum standardized uptake values (SUVmean/max) of the metabolically most active lesion as well as by analyzing clinical parameters (tumor marker doubling times {calcitonin, carcinoembryonic antigen (CEA)}, prior therapies, RET (rearranged during transfection) mutational status, and disease type).
Results: Within a median follow-up of 5.2 years, 9 patients experienced disease progression after a median time interval of 2.1y whereas the remainder had ongoing disease control (n=5 partial response and n=4 stable disease). Eight of the 9 patients with progressive disease died from MTC after a median of 3.5y after TKI initiation.
Pre-therapeutic SUVmean >4.0 predicted a significantly shorter PFS (PFS: 1.9y vs. 5.2y; p=0.04). Furthermore, sustained high 18F-FDG uptake at 3 months with a SUVmean>2.8 tended to portend an unfavorable prognosis with a PFS of 1.9y (vs. 3.5y; p=0.3). Prolonged CEA doubling times were significantly correlated with longer PFS (r=0.7) and OS (r=0.76, p<0.01, respectively). None of the other clinical parameters had prognostic significance.
Conclusions: Pre-therapeutic \(^{18}\)F-FDG PET/CT holds prognostic information in patients with advanced MTC scheduled for treatment with the TKI vandetanib. Low tumor metabolism of SUVmean < 4.0 prior to treatment predicts longer progression-free survival.
Purpose: Prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) imaging has become commonly utilized in patients with prostate cancer (PCa). The PSMA reporting and data system version 1.0 (PSMA-RADS version 1.0) categorizes lesions on the basis of the likelihood of PCa involvement, with PSMA-RADS-3A (soft tissue) and PSMA-RADS-3B (bone) lesions being indeterminate for the presence of disease. We retrospectively reviewed the imaging follow-up of such lesions to determine the rate at which they underwent changes suggestive of underlying PCa.
Methods: PET/CT imaging with \(^{18}\)F-DCFPyL was carried out in 110 patients with PCa and lesions were categorized according to PSMA-RADS Version 1.0. 56/110 (50.9%) patients were determined to have indeterminate PSMA-RADS-3A or PSMA-RADS-3B lesions and 22/56 (39.3%) patients had adequate follow-up to be included in the analysis. The maximum standardized uptake values (SUV\(_{max}\)) of the lesions were obtained and the ratios of SUV\(_{max}\) of the lesions to SUV\(_{mean}\) of blood pool (SUV\(_{max}\)-lesion/SUV\(_{mean}\)-bloodpool) were calculated. Pre-determined criteria were used to evaluate the PSMA-RADS-3A and PSMA-RADS-3B lesions on follow-up imaging to determine if they demonstrated evidence of underlying malignancy.
Results: A total of 46 lesions in 22 patients were considered indeterminate for PCa (i.e. PSMA-RADS-3A (32 lesions) or PSMA-RADS-3B (14 lesions)) and were evaluable on follow-up imaging. 27/46 (58.7%) lesions demonstrated changes on follow-up imaging consistent with the presence of underlying PCa at baseline. These lesions included 24/32 (75.0%) PSMA-RADS-3A lesions and 3/14 (21.4%) lesions categorized as PSMA-RADS-3B. The ranges of SUVmax and SUVmax-lesion/SUVmean-bloodpool overlapped between those lesions demonstrating changes consistent with malignancy on follow-up imaging and those lesions that remained unchanged on follow-up.
Conclusion: PSMA-RADS-3A and PSMA-RADS-3B lesions are truly indeterminate in that proportions of findings in both categories demonstrate evidence of malignancy on follow-up imaging. Overall, PSMA-RADS-3A lesions are more likely than PSMA-RADS-3B lesions to represent sites of PCa and this information should be taken into when guiding patient therapy.