CD81 and B-cell non-Hodgkin lymphoma: The relapsed clone showed an upregulation of S100A4, a driver of tumor cell invasion and metastasis [42] and enhanced expression of CD81, a tetraspanin molecule, which is crucial for the formation and activation of the B cell coreceptor (CD19–CD21–CD81) complex and has recently been proposed as a novel therapeutic target in B cell lymphomas [43].