Therapeutic response assessment of bone metastatic prostate carcinoma treated by abiraterone using x-SPECT Quant®: preliminary results.

Objectives The therapeutic response assessment is a major challenge in patients with bone metastatic prostate carcinoma (BMPC). BMPC progression criteria recommended by the Prostate Cancer Working Group (PCWG2) guidelines [Scher et al. J Clin Oncol 2008] take into account serum PSA level changes or appearance of 2 or more new bone scan lesions. Interpretation of SPECT-CT with a visual analysis limits its performance, making difficult an objective response evaluation. The aim of this prospective study is to assess the feasibility to use a SPECT-CT quantification method for BMPC response evaluation.

Methods Patients with castrate-resistant BMPC treated by abiraterone were prospectively included. Three different double-bed SPECT-CT were planned for each patient (Symbia, Intevo, Siemens®) in our institution: baseline (M0), at 3 (M3) and 6 (M6) months of treatment. SUVmax and SUVpeak quantification were performed using the xSPECT-Quant® software on the highest uptake target lesions (maximum of 5). European Organization for Research and Treatment criteria (EORTC99) [Young et al. Eur J Cancer 1999] and PET Response Criteria in Solid Tumors (PERCIST1.0) [Wahl et al. J Nucl Med 2009] were arbitrarily used as recommended in oncologic PET-CT studies for therapeutic assessment (PR=partial response, SD=stable disease, PD=progressive disease). Results were compared with serum PSA level changes and PCWG2 criteria.

Results Sixteen consecutive eligible patients (74.7 +/- 8.1 years) were included from April 2014 to December 2015. Two patients died before M3 and 4 stopped treatment before M6 due to side effects or obvious PD. Mean SUVmax and SUVpeak on target lesions were respectively 42.8 and 37.1 at M0, 31.2 and 28.5 at M3 and 31.7 and 30.3 at M6. At M3, therapeutic assessment revealed 5 PR, 5 SD, and 3 PD according to EORTC99 criteria and 3 PR, 6 SD and 4 PD according to PERCIST1.0 criteria. Comparatively to M3, therapeutic assessment at M6 revealed 1 PR, 5 SD and 4 PD according to EORTC99 criteria and 1 PR, 6 SD and 3 PD according to PERCIST1.0 criteria. Using EORTC99 and PERCIST1.0 criteria, 80% and 90% therapeutic response assessments respectively matched with both PCWG2 evaluation and serum PSA level changes.

Conclusions These preliminary results show the feasibility to use the xSPECT Quant® software in bone scans interpretation for the response assessment of BMPC treated by abiraterone. To the best of our knowledge, this is the first study evaluating a SPECT-CT quantification tool in a clinical oncologic series.