PTPRC and acute leukemia: Typically, distinguishing between solid tumors and acute leukemia by antigen expression profile analysis is not difficult [20], as the vast majority of AL patients express hematopoietic markers, including the panleukocytic antigen CD45 and markers of either lymphoid or myeloid lineages [61], whereas the immunophenotypes of nonhematopoietic tumors are significantly different, and CD45 negativity is the obligatory feature of nonhematopoietic cells [20].