Metaplasia
In histology, metaplasia is the cytological transformation of a mature epithelium into another that may be closely or remotely related. Metaplasia phenomena are completely normal in embryonic tissues that naturally tend to diversify, mature and specialize their cells. They also take place from totipotent or pluripotent stem cells, depending on whether we speak of embryonic or adult tissues. On certain occasions, metaplasia implies a regression in the specialization or maturation of cells towards more primitive forms to later mature into another class of cells. Metaplasia can occur as a physiological adaptive response to cellular stress and is reversible once the offending stimulus ceases. It is not considered a neoplastic or premalignant lesion. The most common metaplasia is from columnar to squamous epithelium.
However, it is known in human medicine that the transition zone between normal and metaplastic tissue, as it is a very mitotically active zone, can be the seat for the generation of dysplastic cells with the consequent potential for malignancy. [citation required]
In medicine there is controversy in considering intestinal metaplasia of the esophagus (Barrett's esophagus) as a premalignant lesion, but in general terms it is considered as an adaptive mechanism that reverts with the cessation of the stimulus. If the aggressive stimulus persists, it can induce neoplastic transformation from mutations in the cell's genome, with various mutation markers such as inactivation of the P16 and p53 gene.