PROM1 and carcinoma: There are two isoforms of the gene, AC133-1 and -2 (which is 27 nucleotides shorter): it was demonstrated that AC133-2 rather than AC133-1 is the predominant transcript expressed in hematopoietic stem cells (HSCs) derived from fetal liver, bone marrow, and peripheral blood as well as in epidermal stem cells, a wide variety of fetal and adult tissues and several poorly differentiated human carcinomas, but not in more differentiated tumors.