STIM1 and renal cell carcinoma: Based on previous findings, according to which Stim1 is a 77 kDa single-pass transmembrane protein which may undergo post-translational modifications which increase its molecular weight up to 90–100 kDa [37]–[43], these results suggest that RCC-EPCs express two Stim1 variants or forms recognized by the same Ab (see Materials and Methods).