The purpose of this study is to investigate the impact of rituximab in primary breast DLBCL using a matched pair analysis following strict matching criteria in patients with primary breast and nodal DLBCL treated with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) regimen.

Primary breast lymphoma represents 1.7% to 2.2% of all extranodal non-Hodgkin's lymphoma. Histologically, the diffuse large B cell lymphoma (DLBCL) is the most predominant subtype of PBL. Previous studies in the pre-rituximab era have identified the worse outcomes in primary breast DLBCL compared with nodal DLBCL. Few clinical studies have been reported for investigating the efficacy of rituximab in patients with primary breast DLBCL. For clarifying this, a large randomized trial comparing survival in patients with primary breast DLBCL is required. However, the rarity of primary breast DLBCL makes large trial virtually difficult in single center or study group. Additionally, retrospective studies for evaluating the role of rituximab in primary breast DLBCL had bias according to the difference of treatment period between CHOP and R-CHOP era. Thus, in attempt to clarify the impact of rituximab on survival and patterns of progression in patients with primary breast DLBCL, the investigators performed this matched pair analysis following strict matching criteria in patients with primary breast DLBCL, who were identified from our previous nation-wide survey, and nodal DLBCL, who were selected from the data registry of Korean Society of Hematology Lymphoma Working Party, treated with R-CHOP regimen.

Inclusion Criteria:

• Stage I or II of primary breast DLBCL treated with R-CHOP
• Stage I or II of nodal DLBCL treated with R-CHOP

Definition of primary breast DLBCL - Isolated breast involvement with or without nodal disease, which include distant nodal disease as well as regional nodal disease

Definition of nodal DLBCL

- The disease was only limited to the lymph nodes or lymphoid organs

Exclusion Criteria:

• Primary breast DLBCL or nodal DLBCL treated without rituximab
• Secondary breast DLBCL
• Recurrent DLBCL
• Stage III or IV of nodal DLBCL with extranodal involvement as a dissemination process

The primary breast DLBCL group was identified from the nation-wide surveys in the university hospital, general hospital, and cancer institute of Korea. And, the nodal DLBCL group, as a matching control group, was selected from the data registry of Korean Society of Hematology Lymphoma Working Party.