SLC20A1 and cancer: Smaller numbers of cancer cell lines were partially permissive (phenotype 2) or nonpermissive (phenotype 3), with no obvious relationship to the level of expression of receptor PIT-1 mRNA as measured by quantitative reverse transcription-PCR (qRT-PCR), which was in almost all cases higher than that for the permissive HEK293 cell control) (Fig. 1D).