PET/CT Evaluation As a Prognostic Indicator In Relapsed Or Refractory Multiple Myeloma

Background Conventional radiography remains the gold standard imaging modality for staging multiple myeloma (MM). Other imaging modalities have been evaluated in recent years, and been shown to provide additional information about disease burden and location. FDG-PET/CT has proven to be useful in the identification of extramedullary disease and in monitoring patients with non-secretory myeloma. In addition to diagnostic utility, FDG-PET/CT has also been shown to predict time to relapse in the setting of newly diagnosed MM. However, to our knowledge its utility as a prognostic indicator in relapsed or refractory disease has not been studied. Methods We conducted a retrospective analysis of 61 patients with relapsed or refractory multiple myeloma (RRMM) who underwent PET/CT imaging prior to receiving salvage chemotherapy on a therapeutic trial of ClaPD (clarithromycin, pomalidomide, dexamethasone). Patients were heavily pre-treated, having received a minimum of 3 prior lines of therapy (range 3-15). All imaging was performed on the same PET/CT system at a single institution. Each PET/CT was evaluated in blinded fashion by two independent nuclear medicine physicians, with attention to the number and type of lesion, maximum SUV, and presence or absence of extramedullary disease. Disease response evaluation was performed monthly, and measured according to the international uniform response criteria. Multivariate analysis was performed to assess relationships of the above variables to depth of response, progression free survival (PFS), and overall survival (OS). Results Of 61 evaluable patients, 23 (38%) had no lytic lesions, 12 (20%) had 5 lytic lesions on FDG-PET/CT. It is worth noting that 10 patients (16%) were found to have extramedullary disease, 8 of whom had >5 lytic bone lesions. There was no correlation between FDG-PET/CT findings and depth of response or median PFS, however patients with >5 lytic lesions had a median OS of 5.8 months, while it has not yet been reached for the other groups. At a median follow up of 13.2 months, 17 patients (74%) with no lytic lesions and 7 (58%) of those with <5 lytic lesions are alive. Conclusions The presence of >5 lesions on PET/CT at time of relapse is associated with poor prognosis in our cohort of heavily pre-treated patients with relapsed or refractory multiple myeloma receiving salvage chemotherapy with ClaPD. The presence of extramedullary disease, seen mostly in patients with >5 lesions, may contribute to our findings. Further studies in patients with relapsed or refractory MM are needed to evaluate the prognostic utility of FDG-PET/CT in this setting, as well as to extend these findings to other salvage regimens. Disclosures: Rossi: Celgene: Speakers Bureau. Mark: Celgene: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Millennium: Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Onyx: Research Funding, Speakers Bureau. Zafar: Celgene: Speakers Bureau; Millennium: Speakers Bureau; Onyx: Speakers Bureau. Pekle: Celgene: Speakers Bureau; Millennium: Speakers Bureau. Niesvizky: Millennium: The Takeda Oncology Company: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Onyx: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau.