Utility of baseline 18FDG-PET/CT functional parameters in defining prognosis of primary mediastinal (thymic) large B-cell lymphoma

The International Extranodal Lymphoma Study Group ( IELSG) 26 study was designed to evaluate the role of F-18-fluorodeoxyglucose (18FDG) positron emission tomography/computed tomography (PET/CT) in the management of primary mediastinal (thymic) large B-cell lymphoma (PMBCL). We examined the prognostic impact of functional PET parameters at diagnosis. Metabolic activity defined by the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) was measured on baseline 18FDG PET/CT following a standard protocol in a prospectively enrolled cohort of 103 PMBCL patients. All received combination chemoimmunotherapy with doxorubicin-and rituximab-based regimens; 93 had consolidation radiotherapy. Cutoff values were determined using the receiver-operating characteristic curve. At a median follow-up of 36 months, progression-free survival (PFS) and overall survival (OS) were 87% and 94%, respectively. In univariate analysis, elevated MTV and TLG were significantly associated with worse PFS and OS. Only TLG retained statistical significance for both OS (P=.001) and PFS (P<.001) in multivariate analysis. At 5 years, OS was 100% for patients with low TLG vs 80% for those with high TLG (P=.0001), whereas PFS was 99% vs 64%, respectively (P<.0001). TLG on baseline PET appeared to be a powerful predictor of PMBCL outcomes and warrants further validation as a biomarker.