Single Fraction Radiation for Myeloid Sarcoma Is as Effective as Multi-Fraction Regimens for Tumor Regression and Control.

Introduction/background: Myeloid sarcoma is a rare extramedullary manifestation of immature myeloid/monocyte cells. Radiotherapy (RT) yields good local control, but data on different fractionation schemes are limited. The goal of this retrospective study was to share our institutional experience and assess volumetric regression with differential fractionation.

Materials And Methods: We evaluated patients treated for myeloid sarcoma between 2000 and 2019 and categorized them into Group A (treated with RT) and Group B (no RT). We assessed local control using cumulative incidence function analysis. Post-treatment imaging sequences were analyzed for volumetric calculations.

Results: Forty-four patients with 80 lesions were assessed. Twenty-three patients with 52 lesions received RT (Group A), and 6 lesions received a single fraction of RT. There were 2 instances of local progression in Group A and 8 in Group B, with a cumulative incidence function estimate of local progression in Group A of 2.4% at 1 year and 6.9% at 2 years, significantly reduced compared to 29.7% and 35.5% in Group B, respectively (hazard ratio 0.13 [95% confidence interval 0.030.63], P = .011). No lesion treated with a single fraction of RT developed local progression. Volumetric analysis for 19 chronologically followed lesions (including 3 treated with a single fraction) revealed no difference in regression between single or multi-fraction treatment.

Conclusion: RT for myeloid sarcoma yields excellent local control and may be as effective in a single fraction as more protracted courses, though this requires validation. For a diagnosis associated with poor survival, a single palliative fraction may be optimal with potential for higher utilization.