ABCG2 and teratocarcinoma: We also noted that the ABCG2+hox xenograft-derived cells did not form secondary teratomas suggesting that the ABCG2+hox fraction exhibited EC-like characteristics of self-sufficiency for a transient period of time in vivo but did not exhibit the full-blown EC-like malignant phenotype of teratocarcinoma as does Tera-2.