Figure 1
The cancer stem cell theory of tumour development and relapse initiation. An initial oncogenic event (solid arrow) occurring in a normal cell may create a precancerous cell, or directly result in malignant transformation. The oncogenic event is likely to require a number of supporting genetic/epigenetic events (hashed arrows). By the point of clinical diagnosis, the heterogeneous tumour contains cells which have, or are able to activate their stem cell programme and may be able to evade standard therapy. Any cancer stem cells evading therapy are able to divide and differentiate to repopulate the tumour.
