The differential diagnosis includes other malignancies with cutaneous manifestations, such as CD56+ acute myeloid leukemia (AML), RUNX1-mutated AML, Nasal-type extranodal NK/T cell lymphoma, Subcutaneous panniculitis-like T cell lymphoma (SPTCL) and Cutaneous T cell lymphoma. The gene discussed is NCAM1; the disease is primary cutaneous T-cell non-Hodgkin lymphoma.