(A) Spectrum of myeloid dermatoses, including classical Sweet syndrome, histiocytoid Sweet syndrome, the proposed entity of MDS cutis, and leukemia cutis. The morphology of the predominant skin infiltrate in each entity is indicated. The clonality or association of each entity with malignancy is also shown. The most common malignancies are myeloid malignancies. (B) MDS cutis. MDS cells originating in the bone marrow circulate in the peripheral blood, entering the skin and forming a dermal infiltrate with histologic features of so-called histiocytoid Sweet syndrome. On skin biopsy, the infiltrate is MPO⁺, CD33⁺, CD163⁺, MPO⁺, CD34⁻, and CD117⁻. This immunophenotype represents nonblast myeloid precursors at varying stages of differentiation and myelomonocytic cells. DNA sequencing of bone marrow and skin identify the presence of the same mutations, providing evidence that the cutaneous myeloid cells are clonally related to the MDS cells in the marrow. MDS cutis may present as inflammatory plaques or diffuse papulonodular lesions. Lesions may respond to steroids with dependency, although there is frequent response to hypomethylating agents in this study.