The two neoplastic processes in the current case (PV and BPDCN) may be (1) clonally related as described in AML with BPDCN, supporting the theory of evolution of BPDCN from underlying myeloid neoplasms, (2) divergent yet possibly stemming from a common hematopoietic stem cell (possibly the scenario in the presented case, as JAK2 mutation was not detected in the BPDCN involving the skin), or (3) completely unrelated. The gene discussed is JAK2; the disease is CD4+/CD56+ hematodermic neoplasm.