Cancer Stem Cell Principles

The cancer stem cell hypothesis proposes that a cancer maintains a similar hierarchical structure to its normal tissue of origin. Accordingly, the bulk tumor cells would represent the differentiated progeny of rarer cancer cells with stem cell features including self-renewal capacity, that is, the so-called cancer stem cells. Standard therapies currently successfully eliminate the differentiated cancer cells, but the drug-resistant cancer stem cells often remain. Over time, persistent cancer stem cells regenerate the tumor, sometimes at distant sites, leading to relapse and metastasis. Thus, in order to achieve durable remissions in patients, the cancer stem cells must also be specifically targeted. Cells with stem cell characteristics have been found in many hematological malignancies and solid tumors. However, it has been unclear whether they represent laboratory curiosities or actually have clinical relevance. Recent reports showing the persistence of cancer stem cells during remission predicts relapse and provides solid evidence of the clinical relevance of cancer stem cells.