CD56+blastic transformation of chronic myeloid leukemia involving the skin

We report on two patients with chronic myeloid leukemia (CML) who presented blastic transformation involving the skin, with leukemic infiltrates showi ng unusual morphologic and immunohistologic characteristics. Both patients were elderly men with a 36-month and a 40-month history of CML, respectivel y. They presented with disseminated, reddish to violaceous papules and plaq ues (case 1), and with localized reddish nodules on the left temporal area (case 2). Concurrent features of blastic transformation in the bone marrow were observed in one patient (case 1). Histopathologic examination of skin lesions revealed similar features in both cases. There was a moderate to de nse dermal infiltrate composed mainly of medium-sized atypical mononuclear myeloid precursor cells with only few relatively well-differentiated cells of the granulocytic series. Histochemical staining for naphthol-ASD-chloroa cetate esterase revealed strong positivity (>50% of neoplastic cells) in ca se 2 and only scattered positivity (<10% of neoplastic cells) in case 1. Im munohistologic analysis performed on paraffin-embedded sections showed in b oth cases variable reactivity of neoplastic cells for leucocyte common anti gen (CD45), lysozyme, myeloperoxidase, CD11c, CD15, CD43, CD66, CD68, HLA-D R, and the neural cell adhesion molecule (NCAM) CD56. A negative reaction w as observed for CD3, CD34, and TdT. The immunohistologic findings were rema rkably similar to those reported for acute myeloid leukemia (AML) with mono cytic differentiation (French-American-British [FAB] classification, subtyp e M4). Examination of blasts from the bone marrow performed in one patient (case 1) revealed a similar phenotype also with CD56 expression. In conclus ion, our observations show that specific cutaneous infiltrates in CML may s how morphologic and immunohistochemical characteristics similar to those ob served in AML with monocytic differentiation. Moreover, specific cutaneous manifestations of CML may express CD56.