Epithelial Plasticity, Cancer Stem Cells, and the Tumor-Supportive Stroma in Bladder Carcinoma

Abstract

High recurrence rates and poor survival rates of metastatic bladder cancer emphasize the need for a drug that can prevent and/or treat bladder cancer progression and metastasis formation. Accumulating evidence suggests that cancer stem/progenitor cells are involved in tumor relapse and therapy resistance in urothelial carcinoma. These cells seem less affected by the antiproliferative therapies, as they are largely quiescent, have an increased DNA damage response, reside in difficult-to-reach, protective cancer stem cell niches and express ABC transporters that can efflux drugs from the cells. Recent studies have shown that epithelial-to-mesenchymal transition (EMT), a process in which sessile, epithelial cells switch to a motile, mesenchymal phenotype may render cancer cells with cancer stem cells properties and/or stimulate the expansion of this malignant cellular subpopulation. As cancer cells undergo EMT, invasiveness, drug resistance, angiogenesis, and metastatic ability seem to increase in parallel, thus giving rise to a more aggressive tumor type. Furthermore, the tumor microenvironment (tumor-associated stromal cells, extracellular matrix) plays a key role in tumorigenesis, tumor progression, and metastasis formation. Taken together, the secret for more effective cancer therapies might lie in developing and combining therapeutic strategies that also target cancer stem/progenitor cells and create an inhospitable microenvironment for highly malignant bladder cancer cells. This review will focus on the current concepts about the role of cancer stem cells, epithelial plasticity, and the supportive stroma in bladder carcinoma. The potential implications for the development of novel bladder cancer therapy will be discussed. Mol Cancer Res; 10(8); 995-1009. Ó2012 AACR. Bladder CancerWorldwide, an estimated number of 386,300 new cases and 150,200 deaths from bladder cancer occurred in 2008, with the majority of cases (77%) occurring in men. Thereby, bladder cancer is the seventh most common cancer and the ninth most common cause of cancer-related death in men. Bladder cancer is most common in developed countries, where 63% of the cases occurred in 2002. In Europe and the United States, for example, bladder cancer is the fourth most common cancer in males. Overall, the 5-year survival rate of bladder cancer is approximately 80%, and it varies with the stage of the tumor, ranging from 97% for carcinoma in situ to 6% for metastatic disease.Urothelial carcinoma is a heterogeneous disease and multifocal tumors can develop in the same patient. Multifocality can be explained by the monoclonal theory, that is, multiple tumors arise from a single transformed cell or by the field cancerization theory (1). In the latter, exposure of the urothelium to important risk factors for bladder cancer, such as occupational carcinogens induces changes at different sites of the urothelium. As described by Cheng and colleagues (1), urothelial carcinoma in situ is a well-established precursor of invasive bladder cancer and may be...

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