Note: EMT (epithelial mesenchymal transition) and MET (mesenchymal epithelial transition) are opposing processes .Therefore should have theoretically opposite biologies.
Tumor biology is always complex. For this reason it is not easy to talk about "opposite biology". Of course, biology of primary tumour is at least partially different from its metastatic form, but we have to remember that primary toumours have often an intrinsic capacity to undergo EMT. I hope it will be helpfull.
Allow me to make sure if I got your question. Once both EMT and MET are opposing process as you mentioned, I guess that you wonder to know if EMT is a phenomenon that emerges in the context of the primary tumor and does not share any intrinsic particular genetic/epigenetic trait, metabolism profile, active molecular pathway, and so on. What I mean is all of the phenotypic aspects of the EMT are totally different from those present in any cells which compose the primary tumor.