The Role of Radiation Therapy in the Management of Gray Zone Lymphoma.

[PURPOSE] Gray zone lymphoma (GZL) is a rare disease that currently has poor treatment outcomes. The role of radiation therapy (RT) in the management of GZL is not well established. This trial is the largest study to report on the outcomes of patients with GZL treated with and without RT.

[METHODS AND MATERIALS] A retrospective review of 30 patients with GZL treated across 3 institutions from 2009 to 2021 was performed. Treatment response was assessed using end-of-treatment (EST) and/or interim (1) positron emission tomography (PET)-computed tomography or computed tomography scans, per Lugano criteria. A complete response (CR) on an interim PET scan (Deauville score, 1-3) was a rapid-early-response, whereas a partial response (PR) on an interim PET scan without progression was a slow-early-response (SER). For EST assessment, a Deauville score of 1 to 3 was considered CR, and a score of 4 to 5 without progression was considered PR. Event-free survival (EFS) was defined from initiation of frontline chemotherapy to disease progression/relapse, initiation of salvage therapy, or death.

[RESULTS] At a median follow-up of 4 years, the 2-year EFS was 26% for all patients, 33% for RT, and 23% for no-RT (P = .44). The 2-year EFS based on EST was 46% and 10% for CR and PR, respectively (P = .004). Patients with PR to chemotherapy who received RT had significantly better 2-year EFS compared with those who did not (17% vs 0%, P = .007). Among patients with SER, RT was also associated with improved 2-year EFS (33% vs 13%, P = .038). Patients with bulky mediastinal disease had a 2-year EFS of 43% with RT versus 11% without RT (P = .08).

[CONCLUSIONS] Patients with GZL have a high risk of relapse, and RT improves EFS, particularly for patients with SER, PR, and bulky mediastinal disease.