CD7 and T-cell prolymphocytic leukemia: T cell leukemia (T-ALL) commonly expresses the CD7 surface antigen, but it may also be expressed in rare diseases such as, but not limited to, chronic lymphoproliferative disorders of NK cells (CLPD-NK), T cell prolymphocytic leukemia (T-PLL), T large granular lymphocytic leukemia (LGL) and enteropathy-associated T cell lymphoma (EATL) (19, 33–36).