The role of cancer stem cells in neoplasia of the lung: past, present and future.

Through the identification and subsequent targeting of an exquisitely unique and phenotypically defined cancer stem-cell population exhibiting discrete therapeutic vulnerabilities (a potential source of tumor recurrence) better survival rates for these patients may be achieved. It is this impetus that is making the field of pulmonary stem cell biology a growing field in biomedicine. These efforts are leading to the steady identification of multi-potent, self-renewing and proliferative progenitor cell populations throughout the bronchopulmonary tree. These cells give rise to both transiently amplifying (TA) and terminally differentiated (TD) cells, which (like in many other organs) are crucial for tissue homeostasis. In leukemia, it has been shown that partially committed cells, which are normally responsible for tissue maintenance after trauma, may undergo transformation via mutations resulting in the selective expression of genes that accentuate and perpetuate these cells' self-renewal capabilities. It is therefore perhaps legitimate to consider stem cells as protumorigenic. It is when these cells undergo genetic mutations which make them acquire the ability to metastasize, that cancer occurs, rendering the concept of "cancer stem cells" a rather attractive one indeed.