What is a Metaplasia?
Metaplasia is an exquisitely medical term, which tends to generate anxieties and worries in patients due to the phonological similarity with neoplasia, undoubtedly the best known and much feared word.
So let's start by specifying that metaplasia is NOT synonymous with tumor (or neoplasm if you prefer).
We could simplify the concept as much as possible by defining metaplasia as a pre-tumor state, absolutely reversible:
- tumor: abnormal mass of tissue that grows in excess and uncoordinated compared to normal tissues, and persists in this state after the cessation of the stimuli that induced the process
- metaplasia: REVERSIBLE modification in which a differentiated cell type (epithelial or mesenchymal) is replaced by a different cell type. In other words, metaplasia is the CONVERSION OF A NORMAL TYPE OF ADULT CELL INTO ANOTHER TYPE OF NORMAL ADULT CELL. This process of cellular transformation can have a meaning of simple physiological repair or be induced by the need to endure unfavorable environmental conditions, such as hormonal, inflammatory, chemical or physical stimuli. The reversibility character means that when the stimulus that induced the modification it is still possible to recover the original function and structure.
Metaplasia of the smoker
Let's see some examples to better clarify the concept of metaplasia. The image shows enlargements of the cylindrical ciliated epithelium - typical (among other things) of the trachea, bronchi and uterine cervix - and of the stratified squamous epithelium (or multilayered pavement); this last epithelium undoubtedly shows greater resistance to irritative stimuli and is therefore present in the vagina, in the inner lining of the mouth and generally in areas where the more specialized and fragile cylindrical epithelium could not cope with such insults. Well, in heavy smokers the ciliated cylindrical epithelium of the trachea and bronchi is replaced by a stratified squamous epithelium, due to the thermal and irritating effect of cigarette smoke; although the metaplasia described above determines greater resistance to smoking, at the same time it leads to the loss of important protective mechanisms against infections and toxic substances from the external environment (from the secretion of mucus to the pro-excretory action of the ciliated cells of the cylindrical epithelium) .
- Metaplasia is therefore a "double-edged sword and, in most cases, represents an" undesirable alteration. Furthermore, the persistence of the stimulus that leads to the metaplastic transformation can induce the neoplastic transformation, therefore tumor and irreversible, of the metaplastic epithelium. This is why metaplasia can be considered a pre-tumor stage, which requires an immediate treatment aimed at the removal of the stimulus. which led to its formation.
Barrett's esophagus
Barret's esophagus is a precancerous disease that affects the esophagus, sometimes damaging it permanently: due to the repeated acid insults caused by gastroesophageal reflux, the normal tissue lining the esophagus is replaced by an epithelium similar to that of the esophagus. duodenal walls (metaplasia of the esophageal epithelium).
To give an idea, the risk of developing adenocarcinoma in the presence of Barrett's esophagus is estimated at 0.4 - 0.5% PER YEAR per patient. Although Barret's esophagus can be easily treated through the use of drugs specific, in this specific case the regression of metaplasia is difficult to obtain.
