Source Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY.
Hepatocellular carcinoma (HCC) is a rising worldwide cause of cancer mortality, making the elucidation of its underlying mechanisms an urgent priority. The liver is unique in its response to injury, simultaneously undergoing regeneration and fibrosis. HCC occurs in the context of these two divergent responses, leading to distinctive pathways of carcinogenesis. In this review, we highlight pathways of liver tumorigenesis that depend upon, or are enhanced by fibrosis. Activated hepatic stellate cells drive fibrogenesis, changing the composition of the extracellular matrix. Matrix quantity and stiffness also increase, providing a reservoir for bound growth factors. In addition to promoting angiogenesis, these factors may enhance the survival of both pre-neoplastic hepatocytes and activated hepatic stellate cells. Fibrotic changes also modulate the activity of inflammatory cells in the liver, reducing the activity of natural killer and natural killer T cells that normally contribute to tumor surveillance. These pathways synergize with inflammatory signals, including telomerase reactivation and reactive oxygen species release, ultimately resulting in cancer. Clarifying fibrosis-dependent tumorigenic mechanisms will help rationalize antifibrotic therapies as a strategy to prevent and treat HCC.