When dead cells tell tales-cutaneous involvement by precursor T-cell acute lymphoblastic lymphoma with an uncommon phenotype.

The thymic type of precursor T-cell acute lymphoblastic lymphoma (pre-T ALL), an uncommon T-cell malignancy, typically presents as a thymic mass and expresses terminal deoxonucleotidyl transferase, CD7, and cytoplasmic CD3, with variable expression of other markers. Cutaneous presentation in pre-T ALL is highly unusual. We describe a case of pre-T ALL presenting as 2 papulonodular lesions on the face of an otherwise asymptomatic 27-year-old man. Microscopic examination of both lesions revealed a moderate to dense pandermal infiltrate of medium-sized lymphocytes with extensive "crush" artifact, whereas immunohistochemistry revealed positive staining of lesional cells for CD45, CD3, Bcl-2, Ki-67, CD5, CD7, and CD34 but negative staining for CD4, CD8, CD30, CD56, CD10, CD117, anaplastic lymphoma kinase protein, TdT, myeloperoxidase, CD79a, and CD20. Gene rearrangement studies performed on both biopsies identified a clonal population of T lymphocytes. A subsequent computed tomography scan revealed a 9-cm mediastinal mass encasing all major mediastinal vessels, whereas a bone marrow biopsy revealed blasts with an immunophenotype similar to that of the cutaneous lesions. Features unique to this case include the cutaneous presentation and the immunophenotype-absence of CD4, CD8, and TdT with expression of CD34-both highly unusual features for pre-T ALL.