Background: MYC/BCL2 double expression (DE) is associated with poor prognosis in patients with diffuse large B-cell lymphoma (DLBCL) receiving rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP).This study aimed to determine whether the addition of DE to the National Comprehensive Cancer Network Internal Prognostic Index (NCCN-IPI) could improve the prediction of disease progression in patients with DLBCL treated with R-CHOP. Methods: This confirmatory prognostic factor study retrospectively recruited patients with newly diagnosed DLBCL between January 1, 2014, and January 31, 2018, at Ramathibodi Hospital (RA) and Thammasat University Hospital (TU).The follow-up period ended on July 1, 2022. Tumors expressing MYC ≥ 40% and BCL2 ≥ 50% were classified as DE. We calculated the hazard ratios (HR) for progression-free survival (PFS) from the date of diagnosis to refractory disease, relapse, or death. Discrimination of the 5-year prediction was based on Cox models using Harrell’s concordance index (c-index). Results: A total of 111 patients had DE (39%), NCCN-IPI (8%), and disease progression (46%). The NCCN-IPI adjusted HR of DE was 1.6 (95% confidence interval [CI]: 0.9–2.8; P = 0.117). The baseline NCCN-IPI c-index was 0.63. Adding DE to the NCCN-IPI slightly increased Harrell’s concordance index (c-index) to 0.66 (P = 0.119). Conclusions Adding DE to the NCCN-IPI may not improve the prognostic value to an acceptable level in resourcelimited settings. Multiple independent confirmatory studies from a large cohort of lymphoma registries have provided additional evidence for the clinical utility of DE.