On the potential origin and characteristics of cancer stem cells.

The 'cancer stem cell' hypothesis has pointed to a specific target for new cancer therapies. The hypothesis is based on the observation that only the 'cancer stem cell' among the other heterogeneous cancer cells can sustain the growth of the cancer. The goal is to identify biomarkers of 'cancer stem cells' to distinguish them from the 'cancer non-stem cells' and normal adult tissue-specific stem cells. This analyst posits a hypothesis that, although all cancers originated from a single cell, there exist two types of 'cancer stem cells' either by the 'Stem Cell hypothesis' or from the 'De-differentiation hypothesis'. It is proposed that there exist two different 'cancer stem cells'. Some 'cancer stem cells' (a) lack the expression of connexins or gap junction genes and lack any form of gap junctional intercellular communication (GJIC) or (b) they have the expressed connexin-coded proteins for functional GJIC but are dysfunctional by some expressed oncogene. This is consistent with the Loewenstein hypothesis that a universal characteristic of cancer cells is they do not have growth control, nor terminally differentiate. This review speculates the normal organ-specific adult stem cell, that is 'initiated', is the origin of the 'cancer stem cells' with expressed Oct4A gene and no expressed connexin genes; whereas the other cancer stem cell has no expressed Oct4A genes but expressed connexin gene, whose coded protein is dysfunctional. Hence. both types of 'cancer stem cells' lack GJIC, for two different reasons, the selective therapies have to be different for these different cell types.