The cells stain positive for the T-cell antigen CD43, as can be demonstrated in two-thirds of ALCL cases. As expected, a population of non-malignant T-cells also express CD43. Most ALCL tumors express one or more T-cell antigens and more than 90% demonstrate T-cell receptor rearrangements. The CD3 pan T-cell marker is negative in more than 75% of cases, and CD2, CD4, CD5, and CD8 show variable expression. This tumor stained positively for CD5 and CD45 (not shown). ALCL also stains positively for TIA-1, perforin, and/or granzyme B, reflecting the cytotoxic T-cell origin of the tumor.