Safety and Toxicities of Radiotherapy As Consolidation or Cytoreduction Around the Time of Autologous Stem Cell Transplantation for Multiple Myeloma Patients: A Single Center Retrospective Report

Abstract

Introduction The efficacy and safety of palliative radiotherapy (RT) is well established for patients with multiple myeloma (MM). However, little is known regarding the safety of RT as consolidation or cytoreduction among MM patients undergoing autologous stem cell transplant (ASCT). Objectives Given that many MM patients undergo ASCT as part of treatment, we sought to characterize the safety and toxicity profile of peri-transplant RT among patients with MM that underwent ASCT at a large, tertiary-care stem cell transplant center. Methods Eligible patients included those 18 years or older with a confirmed diagnosis of MM that underwent ASCT between January 2009 and June 2018 at the Fred Hutchinson Cancer Research Center. Peri-transplant RT was defined as RT deployed within 3 months of ASCT for the explicit purpose of disease consolidation or cytoreduction, including treating lesions at risk for pathologic fracture. We excluded patients that underwent tandem autologous-allogeneic stem cell transplant and patients that received RT for disease relapse post-transplant. Transplant-related toxicity and infectious complications were graded using Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Results Of 785 MM patients that underwent ASCT, 23 (2.9%) received RT, post-stem cell collection, at our institution in the peri-transplant setting. Demographics, disease characteristics, and treatment data are depicted in figure 1. Seven patients (30%) received RT to treat lesions at risk for pathologic fracture. A total of 18 patients (78%) were hospitalized within 30 days of transplant. Among these patients, 12 patients (52%) experienced grade 3 regimen-related toxicities requiring hospitalization, most frequently nausea, vomiting, and mucositis; 2 patients (9%) experienced grade 2 autologous-pseudo GVHD requiring oral steroids. Twelve patients (52%) experienced grade 3 infectious complications, the majority of which were neutropenic fever. The median time to neutrophil engraftment was 16 days (range 13-20), and the median time to platelet engraftment was 11 days (range 8-14); within this group, subjects who received RT to the hip or pelvic region had similar engraftment times. Conclusion In this analysis of the MM patients who underwent ASCT at our institution, we observed the expected degree of transplant-related toxicity among peri-transplant RT recipients, with most patients requiring hospitalization post-transplant for gastrointestinal toxicity. Peri-transplant RT, including irradiation of the hip or pelvic region (where the majority of hematopoiesis occurs), did not impact on engraftment or incidence of infectious complications. Future work is needed to evaluate whether peri-transplant RT improves disease remission among MM patients that undergo ASCT, and we are in the process of updating disease response rates in these patients.