Clinical features

•Very rare aggressive acute leukemia

•Very commonly affects the skin in addition to the blood and bone marrow; also, lymph nodes & spleen

•B symptoms

•Mostly affects the elderly

•3M:1F

•Head, trunk & extremities

•Bruise-like or erythematous maculopapular lesions, nodules or plaques

•Associations with myelodysplastic syndrome, myelomonocytic leukemia or AML

Histological features

. No epidermal involvement

. Dermal +/- subcutaneous fat infiltrate

. No angioinvasion or angiodestruction

. Monotonous blast cells with gray-blue cytoplasm & irrregular vesicular nuclei with prominent nucleoli

. CD4, CD43, CD56, CD123, CD303, TCF4 & TCL1 +ve

. Variable CD68, CD7, CD33 & TdT +ve

. CD34, MNDA, lysozyme & myeloperoxidase -ve.

. Marked ki67 expression

. Germline B cell and T cell receptor genes

Differential diagnosis

AML & chronic myeloid leukemia can be distinguished by the presence of myeloid markers although distinction can sometimes be very difficult. If too much attention is given to the plasmacytoid morphology, a plamsa cell tumor may be readily excluded with IHC.