Abstract
PURPOSE: Many patients with primary mediastinal B-cell lymphoma (PMBCL) achieve only a partial metabolic response (PMR) after initial systemic therapy. However, limited data exist on their outcomes. This study aimed to characterize outcomes in patients with PMBCL who achieve PMR and identify factors guiding appropriate treatment for these patients. METHODS AND MATERIALS: We reviewed patients PMBCL patients treated at 2 independent cancer centers from January 2009 through September 2021. Using the modified Lugano criteria (2014), end-of-chemotherapy positron emission tomography (PET) scan results were evaluated to assess response. Progression-free survival (PFS) and overall survival (OS) rates from the end-of-chemotherapy PET scan date were estimated using the Kaplan-Meier method. RESULTS: A total of 151 patients with PMBCL aged between 15 and 65 years were initiated on systemic therapy and underwent a fluorodeoxyglucose PET scan to evaluate response. Of these, 55 (36%) achieved incomplete metabolic response (IMR) (Deauville score [DS] 4 or 5): 13 (8%) progressed on systemic therapy (a DS score of 5), and 42 (27%) achieved a PMR (a DS score of 4). The 4-year PFS and OS rates for all patients (N = 55) with IMR were 73% and 72%, respectively. PMR management included consolidative radiation therapy (RT) in 36 patients (86%), further chemotherapy in 3 patients (7%), and observation in 3 patients (7%). Four-year PFS and OS among all patients with PMR were 83% and 81%, respectively, and 89% and 87% among those receiving RT. Patients with PMR with maximum standard unit value (SUVmax) > 5 had a lower 4-year PFS (74%) compared with those with SUVmax ≤ 5 (95%), although this difference did not achieve statistical significance (P = .07). None of the 3 patients with PMR under observation relapsed. CONCLUSIONS: Patients with PMBCL often have an IMR. PMR (a DS score of 4) managed with subsequent RT is associated with excellent outcomes. SUVmax may identify patients who may require more or less intensive treatment.