Response Evaluation Using PET/CT in Multiple Myeloma Patients Undergoing Autologous Transplant
Authors: Ellis-Caleo Tim , Sidana Surbhi , Liedtke Michaela , Iberri David 
Published: February 2021

Introduction
Guidelines recommend PET/CT imaging at diagnosis and for response assessment among patients with multiple myeloma. Despite its increasing availability and use, PET/CT may be limited by a lack of standardized reporting criteria and uncertainty regarding management of patients with discordant results of imaging and conventional biochemical response data. This observational study examines the usage of PET/CT for response assessment and investigates the correlation between biochemical and imaging findings for patients undergoing autologous transplant. We further investigate clinician choices when biochemical and PET/CT results are discordant.
Methods
We queried our institutional database for patients with multiple myeloma undergoing autologous transplant between January 2017 and December 2019. Diagnostic PET/CT (PET-Dx) occurred within 90 days of diagnosis; pre-transplant PET/CT (PET-Pre) was within 60 days prior to transplant; and post-transplant PET/CT (PET-Post) occurred between post-transplant days 30-120. Patients who underwent two or more of PET-Dx, PET-Pre, and PET-Post scans were included in the study cohort. Each PET/CT was graded as positive or negative based on criteria in Zamagni 2011. PET-Pre and PET-Post were graded as response, no change, or progression based on definitions in Hillengass 2019. Biochemical data at the time of each PET/CT were interpreted based on IMWG response criteria. Each pair of imaging/biochemical response assessments was compared and deemed concordant or discordant. When comparing pre- or post-transplant response assessments to diagnostic studies, concordance was defined as PET/CT response and biochemical partial response or better. When comparing post-transplant response assessment to pre-transplant studies, concordance was defined as PET/CT response or no change and biochemical stable disease or better. Management of discordant results was gleaned from clinician notes.
Results
From January 1, 2017 to December 31, 2019, 376 patients underwent autologous transplant at our institution. Of these, 75 patients had one or more PET/CT scans in the prespecified windows, and 37 patients had two more PET/CT scans in the prespecified windows. These 37 patients constitute the study cohort. Table 1 shows baseline demographic information from these 37 patients. Of these 37 patients, 29 (78%) underwent upfront transplant. The remaining 8 (22%) underwent transplant during relapse. The 37 patients generated 82 PET/CT scans of which records for corresponding biochemical results were available for 79 (96%). PET-Dx was positive in 24 of 30 (80%), PET-Pre in 16 of 31 (52%), and PET-Post in 12 of 21 (57%). There were 28 comparisons between PET-Dx and either PET-Pre or PET-Post, of which 3 were discordant (Table 2). There were 14 comparisons between PET-Pre and PET-Post, of which 2 were discordant (Table 3). Within the total 5 discordant cases, management was altered on the basis of the PET/CT in only 1.
Conclusion
Among patients undergoing autotransplant at our center, PET/CT was infrequently used for diagnosis and response assessment during the study period. Most biochemical and PET/CT response assessments were concordant (88%), and only in 1 case did a discordant PET/CT directly change management. This work is limited by its small sample size but suggests that while PET/CT has been well described to provide prognostic information, the results of PET/CT did not appreciably change management in our cohort.

Disclosures
Sidana: Janssen: Consultancy. Liedtke:Adaptive: Membership on an entity's Board of Directors or advisory committees; Caelum: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees.