Extramedullary Leukemia: The Role of Radiation Therapy.
Authors: Patel Kamal M. , De Paula Luciana P. , Holland John M. , Maziarz Richard T. , Marquez Carol M. 
Published: October 2019

Abstract
Introduction
Extramedullary leukemia (EML) will develop in approximately 3% of the patients with acute leukemia. Only a few retrospective studies, and no prospective or randomized studies, have assessed the effectiveness and toxicity of radiation for EML. Here we review the EML patients treated with radiation therapy at the Oregon Health and Sciences University (OHSU) Radiation Oncology department.
Methods and Materials
From 1987 to 2005, 17 patients with EML underwent 20 radiation courses at the OHSU Radiation Oncology department. All patients had either biopsy-proven EML or had pre-established diagnoses of leukemia and were treated for EML as presumptive relapse. Patient data and disease history were either extracted from the patient chart or obtained from the cancer tumor registry. Variables used for analysis included patient age, gender, histological diagnosis, tumor location, radiation dose, fraction size, acute toxicities, last follow up or date of death, disease recurrence site after radiation therapy, initial symptom with presenting EML, effect of radiation on symptom(s), and time to EML. Univariate and multivariate analyses were done. Kaplan-Meier survival curves and Cox regression analyses were generated.
Results
The mean age of our patients was 37.5 years, with a range from 7.4 to 78.5 years. Males made up 76% of the patients population. The most common location for an EML was soft tissue (25%), followed by central nervous system (20%), and mucosal (15%). Surgical intervention was performed in only 5 of the 17 EML patients. The 17 patients received 20 treatment courses. The most frequently used radiation energy was 6 Megavoltage photons (55% of the cases), while the next most common was cobalt 60 (10%) and a mixed energy beam (10%). Radiation therapy was quite effective at relieving symptoms with a 94% response rate and 61% having a complete response. Pain was palliated in 88% of patients, while mass effect was decreased in 100% of patients. The mean radiation dose given was 21.8 Gray (range 10–39.6 Gy). We did not observe a radiation dose response to symptom palliation (Table 1). Leukemia recurrence of any type occurred at a median of 5.8 months from the last day of radiation treatment. There was a low incidence of acute grade 1 or 2 toxicities (39%) and no acute grade 3 or 4 toxicities or late toxicities. Our 17 patients had a mean and median overall survival of 20.7 months and 5.6 months, ranging from less than 1 month to 149 months. Regression and correlation models failed to show any significant prognostic factor (age, gender, quality of radiation, total radiation dose, initial presenting EML symptom, or time from diagnosis of leukemia to diagnosis to EML) influencing overall survival.
Conclusions
The role of radiation in EML is for symptom relief. Low dose radiation provides excellent palliation with minimal toxicity. A radiation dose response was not seen in our small patient population.
Table 1 Radiation Dose response in Extramedullary Leukemia Dose # Patients # Symptoms # symptoms with a response # symptoms with a complete response 10–19.9 Gy 6 7 7 (100%) 4 (57%) 20–29.9 Gy 4 5 5 (100%) 3 (60%) 30 Gy or more 4 6 5 (83%) 4 (80%)