Bone marrow infiltration in diffuse large B-cell lymphoma: impact of 18FDG-PET/CT in detection and prediction of therapy outcome Ibrahim Nasr1, Dalia Hamouda2, Omnia Talaat3, Mohamed Abdel Tawab4, Mohammed Fathy1, Ismail Ali5 1Clinical Oncology and Nuclear Medicine Department, Faculty of Human Medicine, Zagazig University. 2Medical Oncology Department, Faculty of Human Medicine, Zagazig University. 3Nuclear Medicine Unit, Radiation Oncology Department, National Cancer Institute, Cairo University. 4Radiology Department, Faculty of Human Medicine, Alazhar University. 5Radiology Department, Faculty of Human Medicine, Zagazig University, Egypt. Journal: Zagazig University Medical J. Accepted for publication: April 2024 Abstract: Objective: to assess the utility of 18FDG-PET/CT in the detection of bone marrow (BM) infiltration and the prediction of therapy outcomes in patients with diffuse large B-cell lymphoma (DLBCL). Method: This retrospective study included 111 patients with pathologically confirmed DLBCL. They underwent 18FDG-PET/CT imaging twice at initial staging and 2 to 12 months following completion of the recommended therapy. Results: 18FDG-PET/CT is more accurate than bone marrow biopsy (BMB) for the identification of BM infiltration and exhibited 100% sensitivity (SN), specificity (SP), positive predictive value (PPV), negative predictive value (NPV), and accuracy for BM infiltration detection. Patients with avid 18FDG BM uptake has a bad prognosis compared to those with no BM FDG uptake, as it is significantly associated with lower rates of complete metabolic response (CMR) (66% vs. 85.9%; p = 0.019), a higher relapse rate (38.7% vs. 9.1%; p = 0.001), lower four-year relapse-free survival (RFS) (37.4% vs. 90.3%; p = 0.001), a lower five-year overall survival (OS) rate (0% vs. 77.1%; p = 0.034), and a higher death rate (21.3% vs. 6.2%; p = 0.018). Also, patients with axial, multifocal, and diffuse FDG BM uptake have a bad prognosis, lower RFS and OS rates. Conclusion: 18FDG PET/CT imaging provides whole-body mapping for detecting BM infiltration with high SN, SP, and accuracy; it can replace routine BMB in the staging of DLBCL. Avid 18FDG BM uptake is a poor prognostic sign associated with a higher relapse rate and lower rates of CMR and OS.