Myeloid leukemia cutis: a histologic and immunohistochemical review

Background: The histologic diagnosis of myeloid leukemia cutis (LC) can be difficult, requiring confirmatory immunohistochemical stains. Objective: We reviewed 21 biopsy-proven cases of LC with emphasis on the use of immunohistochemistry in the diagnosis. Materials and Methods: Clinical and histologic features were reviewed on 21 cases of biopsy proven LC. Immunohistochemical stains for CD4, CD34, CD56, CD68, CD117, CD123, TdT, lysozyme and myeloperoxidase were performed on 12 with available tissue blocks. Results: Ages ranged from 24 to 88 years (mean = 57), with 12 men: 9 women. Primary hematologic diagnoses included acute myeloid leukemia (n = 14), myelodysplastic syndrome (n = 3), essential thrombocythemia (n = 1) and myeloid leukemia, NOS (n = 3). Monocytic myeloid LC was most common (35%). There was 100% positivity with CD68 and lysozyme. Myeloperoxidase, CD117 and CD34 immunostains were less sensitive in myeloid LC (58%, 33% and 17%, respectively). CD4 was positive in 67%. CD56 was positive in 33%. Conclusion: Myeloid leukemia with monocytic differentiation more commonly involves the skin than other types of myeloid leukemia. CD68 and lysozyme immunostains, although not lineage specific for monocytes/macrophages, are the most sensitive immunostains in the detection of myeloid LC. Myeloperoxidase immunostains are useful, but immunostains for CD117 and CD34 are insufficiently sensitive. CD4 expression is common, but CD56 expression is not.