CD7 is a transmembrane protein which is a member of the immunoglobulin superfamily. This protein is found on thymocytes and mature T cells. It plays an essential role in T-cell interactions and also in T-cell/B-cell interaction during early lymphoid development. CD7 can be aberrantly expressed in refractory anaemia with excess blasts （RAEB） and may confer a worse prognosis. Also, a lack of CD7 expression could insinuate mycosis fungoides （MF） or Sezary syndrome （SS）.