In some aspects, the invention provides a genetically tractable in situ non-human animal model for hepatocellular carcinoma. The model is useful, inter alia, in understanding the molecular mechanisms of liver cancer, in understanding the genetic alterations that lead to chemoresistance or poor prognosis, and in identifying and evaluating new therapies against hepatocellular carcinomas. The liver cancer model of this invention is made by altering hepatocytes to increase oncogene expression, to reduce tumor suppressor gene expression or both and by transplanting the resulting hepatocytes into a recipient non-human animal.The present invention also provides methods for identifying and validating tumor suppressor genes by screening pools of shRNAs that target genomic regions deleted in human cancers, such as human hepatocellular carcinomas. The present invention also provides validated tumor suppressor genes, and methods of inhibiting cell proliferation and / or tumor growth, for example by expression of such tumor suppressor genes.