Inclusion Criteria:

1. Age 18 years.

2. One or two prior lines of therapy for the treatment of DLBCL. Prior stem cell
transplant is allowed (salvage therapy, conditioning therapy and maintenance with
transplant will be considered one prior treatment).

3. Histopathologically confirmed diagnosis of RR DLBCL.

Diagnosis of follicular lymphoma transformed to DLBCL (aka transformed DLBCL) is
allowed.

4. Histopathologically confirmed MYC gene-aberrant (MGA) or MYC protein expressor (MPE)
status by archival tissue samples (collected within 1 year of study entry and/or
within 1 line of prior therapy) or fresh tumor samples by one of the following:

- Local or central laboratory (if local testing is not available) fluorescence in
situ hybridization (FISH) results of MYC translocation, or

- Local or central laboratory (if local testing is not available)
immunohistochemical (IHC) results with expression of MYC 40%, and/or gene copy
number gain by FISH.

5. Confirmed availability of viable tissue (defined as archival tissue collected within
1 year of study entry and/or within 1 line of prior therapy or fresh tumor samples)
for central laboratory FISH and IHC testing and review prior to study dosing.

Exclusion Criteria:

1. Known primary mediastinal, ocular, epidural, testicular or breast DLBCL.

2. Known lymphomatous involvement of the central nervous system (CNS) unless deemed
clear of malignant involvement by cytologic examination of cerebrospinal fluid.
Subjects with known bone marrow involvement will require prior chemoprophylaxis per
local standard to prevent CNS relapse.

3. Known allergy or hypersensitivity to phosphatidylinositol 3 kinase (PI3K) inhibitors
or any component of the formulations used in this study. Prior treatment with an
histone deacetylase (HDAC) inhibitor is not allowed (whereas prior treatment with a
PI3K inhibitor is allowed).

4. Cytotoxic anticancer therapy (e.g., alkylating agents, anti-metabolites, purine
analogues) within 2 weeks of study entry.

5. Radiotherapy delivered to target lesions that will be followed on the study (note:
prior sites of radiation will be recorded).

6. Treatment with experimental therapy within 5 terminal half-lives (t1/2) or 4 weeks
prior to enrollment, whichever is longer.

7. Current or planned glucocorticoid therapy, with the following exceptions:

- Glucocorticoids to reduce the potential for infusion reactions to rituximab are
allowed per institutional guidelines.

- Doses 1 mg/kg/day prednisolone or equivalent glucocorticoid and inhalational
therapies for conditions such as mild chronic obstructive pulmonary disease
(COPD) and asthma are allowed.

- Replacement dosing of steroids (defined as < 30 mg/day hydrocortisone or the
equivalent) is allowed, provided that the steroid dose has been stable or
tapering for at least 14 days prior to the first dose of CUDC-907.

Minimum Eligible Age: 18 Years

Maximum Eligible Age: N/A

Eligible Gender: Both