Cellular and Molecular Biology of Cancer Stem Cells of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death globally. The cancer stem cells (CSCs) of HCC are responsible for tumor growth, invasion, metastasis, recurrence, chemoresistance, target therapy resistance and radioresistance. The reported main surface markers used to identify liver CSCs include epithelial cell adhesion/activating molecule (EpCAM), cluster differentiation 90 (CD90), CD44 and CD133. The main molecular signaling pathways include the Wnt/beta-catenin, transforming growth factors-beta (TGF-beta), sonic hedgehog (SHH), PI3K/Akt/mTOR and Notch. Patients with EpCAM-positive alpha-fetoprotein (AFP)-positive HCC are usually young but have advanced tumor-node-metastasis (TNM) stages. CD90-positive HCCs are usually poorly differentiated with worse prognosis. Those with CD44-positive HCC cells develop early metastases. Those with CD133 expression have a higher recurrence rate and a shorter overall survival. The Wnt/beta-catenin signaling pathway triggers angiogenesis, tumor infiltration and metastasis through the enhancement of angiogenic factors. All CD133+ liver CSCs, CD133+/EpCAM+ liver CSCs and CD44+ liver CSCs contribute to sorafenib resistance. SHH signaling could protect HCC cells against ionizing radiation in an autocrine manner. Reducing the CSC population of HCC is crucial for the improvement of the therapy of advanced HCC. However, targeting CSCs of HCC is still challenging.

Automated summary

Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide. Cancer stem cells (CSCs) in HCC play essential roles in tumor progression, resistance to therapy, and metastasis. Several surface markers, including EpCAM, CD90, CD44, and CD133, are used to identify liver CSCs, and multiple molecular signaling pathways, such as Wnt/beta-catenin, TGF-beta, SHH, PI3K/Akt/mTOR, and Notch, are implicated. Different markers are associated with poor prognosis, advanced tumor stages, early metastasis, and increased recurrence rate. Targeting CSCs and reducing their population is crucial for improving the treatment of advanced HCC.