Radiation Therapy can be Safely Incorporated Into Pre-Transplant Treatment Regimens for Patients With Multiple Myeloma

Abstract

<h3>Purpose/Objective(s)</h3> Primary treatment of multiple myeloma (MM) often involves systemic induction therapy (SIT) followed by autologous stem cell transplant (ASCT). Radiation therapy (RT) is sometimes used for palliation; however, many practitioners avoid RT out of concern that future peripheral blood progenitor cell (PBPC) collection required for ASCT may be compromised. We retrospectively examined the possible effect of RT on PBPC collection. <h3>Materials/Methods</h3> We reviewed the charts of 732 MM patients (pts) seen from 1997–2016 at our institution and included pts who received RT prior to PBPC collection for planned ASCT. RT plans (both MM and non-MM RT) were reviewed to estimate the percentage (%) bone marrow (BM) treated using published estimates of skeletal BM distribution. Statistics were performed using Pearson correlations and t-tests. <h3>Results</h3> Of 732 MM pts, ASCT was planned for 485 pts; of these, 223 pts received RT prior to PBPC collection and were included in the final cohort. 133 pts (60%) were male. Median age at PBPC collection was 59 years (range 33—80). For SIT, pts received combination regimens including the following agents: bortezomib (142 pts, 64%); lenalidomide (111 pts, 50%); alkylators (46 pts, 21%). Nine pts (4%) received dexamethasone alone. RT plans and/or a description of the fields, were available to estimate treated BM% for 221 pts. The median cumulative BM% treated per pt was 6.7 (range 0.0—47.4). The median RT dose was 24 Gy (range 10.0—75.6 Gy). Mobilization was performed using granulocyte-colony stimulating factor (G-CSF) alone (189 pts, 85%), G-CSF with plerixafor (15 pts, 7%), or chemotherapy (19 pts, 8%). PBPC collection data was available for 199 pts. A median of 7.8 × 10⁶ CD34⁺/kg PBPCs (range 0.5—54.8) were collected in a median of 3 (1—9) apheresis procedures. 196 pts (99%) collected more than 2.0 × 10⁶ CD34⁺/kg (minimum PBPC no. required for engraftment), and 167 pts (84%) collected more than 5.0 × 10⁶ CD34⁺/kg (preferred no. of PBPCs collected). The number of PBPCs collected was not associated with BM% treated (<i>P</i> = 0.15) or RT dose (<i>P</i> = 0.56). The number of apheresis procedures performed was not associated with BM% treated (<i>P</i> = 0.54) or RT dose (<i>P</i> = 0.85). The number of PBPCs collected did not differ significantly for pts receiving RT to the pelvis (<i>P</i> = 0.96), lumbar spine (<i>P</i> = 0.35), or thoracic spine (<i>P</i> = 0.059). Time to platelet engraftment was longer for patients with higher %BM treated (<i>P</i> = 0.02). Eleven pts did not undergo a confirmed ASCT due to: pt preference (3 pts), trial therapy (1 pt), comorbidities (1 pt), election for hospice (1 pt), inadequate collection (4 pts) and inadequate follow up (1 pt). <h3>Conclusion</h3> Among pts with MM, RT prior to ASCT did not prevent adequate PBPC collection or impair successful ASCT. RT must be carefully planned and delivered to ensure safe incorporation into pre-ASCT treatment regimens.