DLT was defined as any of the following toxicities, possibly or probably related to cerdulatinib, and clinically significant (in the judgement of Investigator): -Febrile neutropenia (absolute neutrophil count \<1000/microliter \[μL\] and temperature ≥38.5°Celcius). -Grade 4 neutropenia for \>5 days. -Grade 4 thrombocytopenia with or without bleeding. -Grade 3 thrombocytopenia with bleeding. -Grade 4 anemia, unexplained by underlying disease. -Grade 3 or greater nausea, vomiting, or diarrhea if persistent despite optimal antiemetic or anti-diarrheal therapy. -Grade 3 or greater increase in transaminases lasting \>5 days. -Grade 3 or greater fatigue persisting \>7 days in absence of any other underlying cause. -Any other Grade 3 or greater non-hematologic toxicity (except fatigue as noted above) considered clinically significant by Investigator. -Toxicity of any grade resulting in dose delay of \>7 days. -Toxicity resulting in study drug discontinuation prior to completion of Cycle 1.

CR included: -Via a positron emission tomography (PET)/computed tomography (CT) scan, score of 1 (no uptake above background), 2 (uptake of \<mediastinum), or 3 (uptake of \>mediastinum but \<liver) for lymph nodes and extralymphatic sites; no new lesions; and no evidence of fluorodeoxyglucose (FDG)-avid disease in bone marrow. -Via CT scan, target nodes/nodal masses regressed to \<1.5 centimeters (cm) in longest transverse diameter of a lesion (LDi); no extralymphatic sites of disease; organ enlargement has regressed to normal; and bone marrow was normal by morphology and if indeterminate, immunohistochemistry was negative. PR included: -Via a PET/CT scan, score of 4 (uptake of moderately \>liver) or 5 (uptake markedly higher than liver and/or new lesions) with reduced uptake compared with baseline and residual masses of any size. -Via CT scan, \>50% decrease in the sum of the product of perpendicular diameters for multiple lesions of up to 6 target measurable nodes and extranodal sites.