CD9 and neoplasm: Severalstudies suggest that CD9 and CD81 expression may have a clinical significancein neoplastic diseases, but these are usually not seen as specificenough to represent a clear diagnostic tool.60−65 In fact, the results shown in Figure 4 indicate significant variations in the concentrationdetected between healthy individuals (see also Supporting Information section 7 and Figure S8 for more details).Variations may also occur over time for the same healthy individual,something we did not explore.