HPCs normally reside in biliary ducts and can be activated by impairment of hepatocyte replicative potential during chronic liver damage.[5] Thorgeirsson et al found that a distinct subtype of aggressive HCC expresses HPC markers, suggesting that this subtype of HCC might arise from HPCs.[6] Markers of cancer stem cells (including EpCAM, CD133, CD24, and CD44), specific cytokeratins (including CK7 and CK19), CLDN4, and the transcription factor Sox9[7] can be used to identify HPCs. The gene discussed is SOX9; the disease is hepatocellular carcinoma.