CD7 is a single-pass type 1 transmembrane protein that is a member of the immunoglobulin superfamily. It plays an essential role in T-cell interactions and also in T-cell/B-cell interactions during early lymphoid development. CD7 is expressed on thymocytes, T- and natural killer cells, and progenitors of lymphoid and myeloid cells. It is also expressed on T-cell Acute Lymphoblastic Leukemia/Lymphoma, Acute Myelogenous Leukemia, and Chronic Myelogenous Leukemia. CD7 antibody is the most sensitive and specific T-cell deletion marker. Loss of CD7 expression by neoplastic lymphocytes is considered a distinguishing characteristic of mycosis fungoides (MF) and cutaneous T-cell lymphoma.