Three key features are of note. o Only replaced between D homologous tissues(most commonly involves epithelium or occurs in mesenchymal tissue To arise by reprogramming of stem cells to differentiate along a new pathway rather than a phenotypic change(transdifferentiation)of Stem cell already differentiated cells Three key features are of note.  Only replaced between homologous tissues (most commonly involves epithelium or occurs in mesenchymal tissue )  To arise by reprogramming of stem cells to differentiate along a new pathway rather than a phenotypic change (transdifferentiation) of already differentiated cells