The existence or non-existence of tumor stem cells has been a matter of endless academic debate in recent years. To address this issue, Muhammad Alamgeer from the Department of Oncology at Monash Medical Centre, Australia, reviews the relevant literature and addresses some of the controversial issues. Published in the April 16, 2013 issue of Resppirology, the article reviews some of the recent experimental and clinical research on cancer stem cells, discusses some of the relevant issues, and offers some ideas. The cancer stem cell theory is based on numerous experimental and clinical observations showing that a small number of cells with self-replication, differentiation and innate resistance to radiotherapy can lead to the persistence of a malignant phenotype. It is possible that cancer stem cells, which are functionally equivalent to microscopic lesions, are responsible for cancer recurrence after eventual treatment. Similar to other solid tumors, a number of recognized surface markers of lung cancer stem cells have been identified, including CD133 and CD44, and the relationship between high cytoplasmic expression of acetaldehyde dehydrogenase, cell membrane permeability dye exclusion (known as the “side population”) and cancer stem cells in vivo and in vitro has also been clarified. . Embryonic stem cell pathways such as the Hedgehog signaling pathway, Notch signaling pathway, and Wnt signaling pathway may also be highly expressed in lung cancer stem cells. The goal of these studies is to provide long-term maintenance therapy for patients after surgery or after complete remission after radiotherapy. Cancer stem cell theory is a very important theoretical model of tumor biology, which well explains some innate drug-resistant cancer cells and presents a wonderful vision for long-term maintenance therapy for cancer patients. Cancer stem cells have not been found to have sufficiently specific markers so far, and the evidence for their existence is still insufficient. But some related studies provide new therapeutic strategies and approaches for future tumor treatment.