Immunohistochemistry, quantitative reverse transcriptase PCR, and microarray analysis all revealed PXR expression in carcinoma tissues but not in nonneoplastic or stromal cells in breast carcinoma patient samples. In breast carcinoma cells, pharmacologic activation of PXR via rifampicin increased PXR target genes (OATP1A2 and CYP3A4). Positive correlation between PXR, OATP1A2, and increasing tumor grade in breast carcinoma patient samples. This evidence concerns the gene CYP3A4 and neoplasm.