18F-Clofarabine (CFA) as a PET Imaging Agent to Measure Deoxycytidine Kinase (DCK) Activity in Metastatic Cancer, as a Candidate Predictive Biomarker for Response to DCK-dependent Drugs Such as Gemcitabine

Inclusion Criteria: * Histologically or cytologically proven metastatic cancer (including carcinoma, adenocarcinoma, sarcoma, or neuroendocrine cancer). * Subjects must have metastatic disease, confirmed by imaging, typically a CT scan of the chest/abdomen/pelvis. * Subjects must have measurable disease per RECIST 1.1 * Over 18 years of age * ECOG performance status 0-1 * Adequate organ function as defined by the following criteria (labs may be no more than 4 weeks prior to the screening date): * Serum aspartate transaminase (AST; serum glutamic oxaloacetic transaminase \[SGOT\]) and serum alanine transaminase (ALT; serum glutamic pyruvic transaminase \[SGPT\]) \<= 2.5 x laboratory upper limit of normal (ULN) * Total serum bilirubin \<= 2.0 x ULN * Absolute neutrophil count (ANC) \>= 1500/uL * Platelets \>= 75,000/uL * Hemoglobin \>= 8.0 g/dL * Serum calcium \<= 12.0 mg/dL * Serum creatinine \<= 2.9 mg/dL * Subjects must have the ability to understand and the willingness to sign a written informed consent document * Patient is able to remain still for the duration of the imaging procedure (up to one hour). Exclusion Criteria: * Within 6 months prior to enrollment on this study: myocardial infarction, severe/unstable angina, severe peripheral vascular disease (claudication) or procedure on peripheral vasculature, coronary/peripheral artery bypass graft, New York Heart Association grade II or greater congestive heart failure, cerebrovascular accident or transient ischemic attack, clinically significant bleeding or pulmonary embolism. * Pregnancy or breastfeeding (pregnant or breastfeeding women are excluded from this study because study drugs have the potential for teratogenic or abortifacient effects. * Other severe acute or chronic medical or psychiatric conditions or laboratory abnormalities that may increase the risk associated with study participation or study drug administration, or may interfere with the interpretation of study results, and in the judgment of the investigator would make the patient inappropriate for entry into this study.