to explain the differences of cytokeratin patterns between these tumours and normal epithelium as well as between different forms of squamous cell carcinomas two hypotheses are discussed , i.e . clonal selection of certain cells present in the original epithelium , probably in the basal layer ( s ) , and different pathways of differentiation in the cell progeny derived from the transformed cell ( s ) of origin .
C0007137
squamous
C0014609
epithelium