T-cell prolymphocytic leukemia frequently shows cutaneous involvement and is associated with gains of MYC, loss of ATM, and TCL1A rearrangement

T-cell prolymphocytic leukemia (T-PLL) is a rare aggressive mature T-cell leukemia with frequent cutaneous presentation, which has not been well characterized. Among the 25 T-PLLs diagnosed between 1990 and 2013 at our institution, 32% (8/25) showed cutaneous manifestations, presenting as rash, purpura, papules, and ulcers. The skin biopsies showed leukemia cutis with perivascular and periadnexal irregular, small to medium-sized lymphoid infiltrates without epidermotropism. The lymphoid infiltrates were composed of mature CD4⁺ T cells expressing other T-cell antigens, and a subset (48%) showed dual CD4⁺/CD8⁺ coexpression. Higher median absolute peripheral blood lymphocyte count (43.0 vs. 13.0k/mm³; P=0.031) and elevated lactate dehydrogenase levels (P=0.00018) at the time of diagnosis were significantly associated with T-PLLs with skin involvement compared with those without. The extent of bone marrow involvement (P=0.849) and overall survival (P=0.144) was similar in the 2 groups. Fluorescence in situ hybridization or karyotype revealed frequent gains of MYC (67%; n=9), loss of ATM (64%; n=11), and TCL1A rearrangement or inversion 14q (75%; n=12). Gains of TCL1A was also seen (78%; n=9), including in some cases that had concurrent TCL1A rearrangement, whereas TP53 loss was less common (30%; n=10). No correlation was seen between the immunophenotype and morphology versus the presence or absence of skin involvement. These data suggest that cutaneous involvement by T-PLL is relatively common and often associated with significant peripheral blood involvement. The frequent MYC, ATM, and TCL1A alterations identified support that these genes are integral to the pathogenesis of T-PLL.