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