Hematologic Malignancies

PV 01 - Poster Viewing Q&A - Session 1

SU_15_3101 - The Impact of PET-CT on Rates of Progression from Solitary Plasmacytoma to Multiple Myeloma after Definitive Radiation Therapy

Sunday, September 15
1:15 PM - 2:30 PM
Location: ASTRO Innovation Hub

The Impact of PET-CT on Rates of Progression from Solitary Plasmacytoma to Multiple Myeloma after Definitive Radiation Therapy
C. P. Anakwenze1, J. R. Gunther1, E. E. Manasanch2, S. S. Noticewala1, S. A. Milgrom1, H. Lee2, K. Patel2, S. Thomas2, S. P. Iyer3, D. Weber2, C. Park4, B. Amini5, J. Khoury2, L. J. Medeiros6, R. Orlowski2, B. Dabaja1, and C. C. Pinnix7; 1MD Anderson Cancer Center, Division of Radiation Oncology, Houston, TX, 2MD Anderson Cancer Center, Houston, TX, 3MD Anderson Cancer Center, Department of Lymphoma and Myeloma, Houston, TX, 4Vanderbilt University, Nashville, TN, 5MD Anderson Cancer Center, Department of Radiology, Houston, TX, 6MD Anderson Cancer Center, Department of Hematopathology, Houston, TX, 7The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Diagnostic criteria for solitary plasmacytoma (SP) have evolved as baseline testing has improved. 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) and more sensitive bone marrow (BM) evaluation has facilitated the diagnosis of SP through the identification of patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance (MGUS). We hypothesized that SP patients treated with radiation therapy (RT) after thorough staging with PET-CT and BM evaluation for small populations of clonal plasma cells (cPC) will exhibit a lower rate of MM progression than those evaluated with conventional diagnostic testing.

Materials/Methods: After IRB approval, 100 SP patients treated with RT between 2000 and 2017 were reviewed. Twenty-one patients were excluded because: RT at another institution (n=14), 2 distinct disease sites identified during workup (n=5), chemotherapy before RT (n=1) and no follow up after RT (n=1). The impact of pre-treatment PET-CT and BM cPC assessment (with flow cytometry and/or immunohistochemistry) on the risk of progression to MM and overall survival (OS) was assessed. All survival endpoints were from the diagnosis date using the Kaplan-Meier method.

Results: The final cohort was 79 patients. The median age at diagnosis was 57.5 years, 62% (n=49) were men and 75% (n=59) had bone SP. PET-CT was performed, confirming a single contiguous site of disease in 53.2% of patients (n=42). In the diagnostic BM sample, the median plasma cell % was 2 (0-6%). Clonality was assessed in 56 (70.9%) patients and was positive in 11% (n=6). The median RT dose was 45 Gy. The median follow up was longer in the non-PET-CT cohort (13.9 years) versus the PET-CT cohort (4.8 years, p<0.01). At a median follow up of 9.3 years the 5 year OS was 88.8%. The 5 year progression to MM was 48.6% among bone SP patients (n=59) and 20% in extraosseous SP patients (n=20 p=0.01). Among bone SP patients, the 5-year progression to MM was 49.5% in the non-PET-CT cohort (n=28) and 55.5% in the PET-CT cohort (n=31, p=0.51). For extraosseous SP patients, the 5-year progression to MM was 44.4% for those without PET-CT (n=9) and 0% for patients with PET-CT staging (n=11, p=0.015). Patients with cPCs had a higher 5-year rate of progression to MM (n=6, 75%) compared to those without (n=50, 37%, p=0.02). There was a trend towards a lower 5-year rate of progression to MM for patients who had PET-CT performed confirming one site of disease and no cPCs present (n=34, 34.4%) compared to those without both confirmatory assessments (n=45, 46.8%, p=0.06).

Conclusion: The use of contemporary staging methods for SP, by excluding disease elsewhere that was occult using older staging methods, may be refining the classification of SP and therefore impacting the rate of progression to MM after definitive RT. Larger studies are required to determine the role of these tests in the diagnosis of SP.

Author Disclosure: C.P. Anakwenze: None. J.R. Gunther: None. S.S. Noticewala: None. H. Lee: None. K. Patel: None. S. Thomas: None. C. Park: None. L.J. Medeiros: None. R. Orlowski: None. C.C. Pinnix: Consultant; Global Oncology One. Research Grant; Merck & Co.

Chidinma Anakwenze, MD, MPH

MD Anderson Cancer Center

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