The role of frontline therapy of autologous stem cell transplant (ASCT) in diffuse large B-cell lymphoma (DLBCL) is controversial. The investigators aim to conduct this prospective study to observe the efficacy and safety of ASCT as frontline therapy in DLBCL patients with high-risk disease, defined by an International Prognostic Index (IPI) score equal to or greater than three.

There is evidence to suggest that chemotherapy followed by ASCT may be more effective than standard chemotherapy alone as a frontline treatment for high-risk DLBCL patients. However, the use of ASCT as frontline therapy for DLBCL remains controversial due to concerns over the potential toxicities of the procedure, as well as questions about which patients would benefit most from this approach.

The investigators aim to conduct this prospective study to observe the efficacy and safety of ASCT as frontline therapy in DLBCL patients with high-risk disease, defined by an International Prognostic Index (IPI) score equal to or greater than 3 points.

Patients diagnosed with DLBCL and an IPI score of equal to or greater than three will be eligible for inclusion in this study, provided they consent to receive the standard R-CHOP (Rituximab, cyclophosphamide, hydroxydaunomycin, oncovin, and prednisone) regimen, followed by ASCT. During the interim evaluation, patients achieving complete response (CR) as determined by computed tomography (CT), or complete metabolic response (CMR) as determined by positron emission tomography-computed tomography (PET-CT), will be followed up for up to two years after completing the R-CHOP regimen followed by ASCT. Patients achieving partial response (PR) as determined by CT, or partial metabolic response (PMR) as determined by PET-CT, and who are willing to receive Pola-R-CHP (Polatuzumab vedotin, rituximab, cyclophosphamide, hydroxydaunomycin, and prednisone) as the following treatment regimen followed by ASCT with Pola-BEAM (Polatuzumab vedotin, carmustine/bendamustine, etoposide, cytarabine and melphalan) as conditioning regimen, will also be followed up for up to two years. Patients achieving less than a PR or PMR response will be excluded from the study.

Inclusion Criteria:

• Previously untreated participants with cluster of differentiation 20 (CD20)-positive DLBCL, including one of the following diagnoses by 2016 World Health Organization (WHO) classification of lymphoid neoplasms: DLBCL, not otherwise specified (NOS) including germinal center B-cell type, activated B-cell type; T-cell/histiocyte-rich large B-cell lymphoma; Epstein-Barr virus-positive DLBCL, NOS; anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma; human herpesvirus-8 (HHV8)-positive DLBCL, NOS; High-grade B-cell lymphoma with MYC and B-cell lymphoma 2 (BCL2) and/or B-cell lymphoma 6 (BCL6) rearrangements (double-hit or triple-hit lymphoma); High-grade B-cell lymphoma, NOS
• Measurable tumor assessed by Lugano Response Criteria
• International Prognostic Index (IPI) score equal to or greater than 3 points
• Adequate hematologic function
• Adequate liver function
• Adequate kidney function
• Left ventricular ejection fraction (LVEF) >/= 50 percent (%) on cardiac echocardiogram (ECHO)

Exclusion Criteria:

• Contraindication to any of the individual components of CHOP, including prior receipt of anthracyclines
• Participants with central nervous system (CNS) lymphoma (primary or secondary involvement)
• History of other malignancy that could affect compliance with the protocol or interpretation of results

Patients diagnosed with DLBCL and an IPI score equal to or greater than three and consent to receive the standard R-CHOP regimen followed by ASCT. During the interim evaluation, patients achieving CR or CMR, will be followed up for up to two years after completing the R-CHOP regimen followed by ASCT. Patients achieving PR or PMR and who are willing to receive Pola-R-CHP as the following treatment regimen followed by ASCT, will also be followed up for up to two years. Patients achieving less than a PR or PMR response will be excluded from the study.