Liver Cancer: Stem and Progenitor Cells

Abstract

Stem cells are involved in hepatocarcinogenic pathways. In the normal liver, hepatic stem cells are self-renewing cells dwelling in distinct compartments termed stem cell niches. These niches are distinct microenvironments which maintain the balance of slow selfrenewal of quiescent stem cells and their priming to become hepatocytes and other differentiated cells. Hepatic stem cells possess plasticity, allowing them to undergo lineage diversification. In hepatocarcinogenesis, tumor stem cells mimick certain features of their normal counterparts. Tumor stem cells in hepatocellular carcinoma (HCC) can act as tumor-initiating cells and tumor-propagating cells that express hepatic stem cell markers and show distinct gene expression profiles. Apart from their role in carcinogenic pathways, cancer stem cells in HCC are considered to play an important role in tumor recurrence and metastasis. The expression of stemnessrelated markers in HCC confers an aggressive phenotype in these neoplasms. Tumor stem cells in HCC modulate several processes, including maintenance of slowly cycling clonogenic cells having longevity, induction of distinct growth features, and tumor progression. Following removal of HCC and other liver cancers, tumor stem cells can remain in the liver and enter the bloodstream to settle in new stem cell niches, including metastatic niches.