RecruitingEarly Phase 1Drug trialIn-Human CXCR4 Imaging of Hematologic and Solid Tumors Using [68Ga]-Pentixafor-PETThe purpose of this study is to determine the uptake of the imaging agent \[68Ga\]-pentixafor with PET/CT scans in people with monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM), and non-Hodgkin lymphoma (NHL), or you have histiocytic neoplasms (Langerhans cell histiocytosis (LCH), Erdheim-Chester disease (ECD) and/or Rosai-Dorfman disease (RDD).