(HR: 2.66, 95% CI: 1.63-4.34), whereas only bone marrow involvement at FDG-PET/CT was reported to be a predictor of PFS and OS in the multivariate analysis. El-Galaly et al.[1] concluded FDG-PET/CT to be highly sensitive for the detection of extranodal involvement and claim bone marrow involvement at FDG-PET/CT to be highly predictive of outcome.However, we cannot agree with El-Galaly et al.'s statement that FDG-PET/CT has high sensitivity for the detection of extranodal/bone marrow involvement, since this statement is simply not supported by their own data. Although increased bone marrow FDG uptake at PET/CT was observed much more frequently than lymphomatous involvement of the bone marrow biopsy specimen, increased FDG uptake of the bone marrow was not observed in 12/45 (26.7%) of patients with histologically proven largecell (aggressive) lymphoma, and in 18/28 (64.3%) of patients with histologically proven small-cell (indolent) lymphomatous bone marrow involvement. Note that the suboptimal sensitivity of FDG-PET/CT for the detection of bone marrow involvement has already been demonstrated by several other studies [2], and that the sensitivity of all these previous studies might even be overestimated, since they all performed a patient-based analysis rather than a local comparison between FDG-PET/CT and bone marrow biopsy findings. When a local, head-to-head comparison between FDG-PET/CT and BMB in the posterior iliac crest is performed, the sensitivity of FDG-PET for bone marrow involvement has been reported to be even lower [3]. Finally, note that the bone marrow is usually the only extranodal site that is additionally biopsied in patients with histologically proven DLBCL. Due to the lack of a reference test the sensitivity of FDG-PET/CT for the detection of extranodal involvement other than the bone marrow is actually unclear.Another important issue is that El-Galaly et al.[1] reported bone marrow involvement as detected by FDG-PET/CT to be highly predictive of PFS and OS, and that it would surpass the prognostic value of BMB. However, this highly contradicts the results of previous studies on this topic [4-8], which were not correctly discussed by El-Galaly et al. [1]. Of these five previous studies on the prognostic value of FDG-PET/CT-based bone marrow involvement, four studies [4,5,7,8] showed that pathological bone marrow FDG uptake has no prognostic value at all, and the only previous study that reported FDG-PET/CT-based bone marrow involvement to have any prognostic value clearly showed that bone marrow FDG-PET was prognostically inferior to BMB [6]. That particular study reported bone marrow FDG-PET/CT negative patients to have 2-year PFS and OS of 84.5% and 88.5%, and bone marrow FDG-PET/CT positive patients to have 2-year PFS and OS of 62.5% and 76.1%, respectively [6]. However, the 2-year PFS and OS of BMB-negative patients were 82.1% and 87.2%, and those of BMB-positive patients were 37.5% and 62.5%, respectively, which clearly shows that BMB is better at selecting patients with a worse prognos...