Although the topology of renal NaPi2a (Lambert et al., 1999, 2000), as well as of the flounder NaPi2b (Kohl et al., 1998) with large extracellular domain/loop (ECD/ECL) and C- and N-termini facing the cytoplasm was predicted and verified by the heterologous expression of FLAG-tagged and untagged templates in Xenopus laevis oocytes, it is not known whether the topological arrangement of the largest extracellular domain facing outside and the N- and C-termini facing the cytoplasm is conserved for all the SLC34 proteins, especially in cancer cells. Here, SLC34A1 is linked to cancer.