Inclusion Criteria:

   - Male or female subjects aged 18 years or older

   - Histologically confirmed primary DLBCL of any stage

   - Refractory to the last treatment regimen

   - Previously treated with the following treatment regimens:

   - Anthracycline-based combination chemotherapy with rituximab

   - Second-line combination chemotherapy

   - Autologous BMT if the subject was eligible and did not refuse the procedure

   - At least one measurable lesion defined as > 1.5 cm in the longest diameter

   - No known central nervous system involvement

   - ECOG performance status < 2

   - Life expectancy > 12 weeks

   - If female, non-pregnant and non-lactating

   - IRB-approved consent and HIPAA Authorization

Exclusion Criteria:

   - Transformed, composite or discordant lymphoma

   - Therapy for lymphoma within 21 days prior to the first dose of YM155

   - Within 4 weeks of the screening FDG-PET scan, receipt of the following:

   - Radiation therapy

   - Surgical procedures (except biopsies and central catheter / port placement)

   - Active infection (bloodstream or deep tissue)

   - Inadequate marrow, hepatic and/or renal function

   - Serum creatinine > 1.5 x ULN or calculated serum creatinine clearance < 60 mL/min

   - Absolute Neutrophil Count (ANC) < 750/mm3

   - Platelet < 50,000/mm3

   - Alanine Transaminase (ALT) and Aspartate Transaminase (AST) > 2.5 x ULN; > 5 x ULN if
   secondary to liver metastases

   - Treated with > 3 prior treatment regimens. The following should be considered:

   - Planned maintenance therapy should be considered as part of the previous treatment
   regimen

   - Any preparative treatment (salvage chemotherapy, high-dose chemotherapy, radiation
   therapy, etc.) should be included with the autologous BMT or PBSCT as one treatment

   - Prior allogeneic BMT or PBSCT

   - Previously treated with YM155

   - Other investigational therapy or procedures within 28 days

   - Known HIV, hepatitis B surface antigen, or hepatitis C antibody

   - Other malignancy requiring treatment within 2 years

   - Significant and/or uncontrolled cardiac, renal, hepatic, or other systemic disorders
   or significant psychological conditions that in the Investigator's judgment would
   jeopardize subject enrollment or compliance