What is a Metaplasia?
Metaplasia is a purely medical term, which tends to generate anxieties and concerns in patients because of their phonological similarity with neoplasia, a word that is certainly better known and much feared.
So let's start by specifying that metaplasia is NOT synonymous with tumor (or neoplasm if you prefer).
We could simplify the concept to the maximum by defining metaplasia as a pre-tumor state, absolutely reversible:
- tumor : abnormal mass of tissue that grows in excess and in an uncoordinated way 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 IN ANOTHER TYPE OF ADULT NORMAL CELL. This process of cellular transformation can have the meaning of simple physiological repair or be induced by the need to withstand unfavorable environmental conditions, such as hormonal, inflammatory, chemical or physical stimuli. The character of reversibility means that when the stimulus that induced the modification ceases, it is still possible to recover the original function and structure.
Metaplasia of the smoker
Let's look at some examples to better clarify the concept of metaplasia. The image shows enlargements of the cylindrical cylindrical epithelium - typical (among other things) of the trachea, bronchi and cervix - and stratified squamous epithelium (or paved multi-layer); the latter 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 the areas where the more specialized and fragile cylindrical epithelium could not face such insults. Well, in hardened smokers the cylindrical cylindrical epithelium of the trachea and bronchi is replaced by a stratified squamous epithelium, due to the thermal and irritative effect of cigarette smoke; although the metaplasia described above results in 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 hair cells of the cylindrical epithelium) .
- Metaplasia is therefore a double-edged sword and, in most cases, represents an unwanted alteration. Furthermore, the persistence of the stimulus that leads to the metaplastic transformation can induce the neoplastic transformation, therefore tumoral and irreversible, of the metaplastic epithelium. This is why metaplasia can be considered a pre-tumor stage, which requires an immediate treatment aimed at removing the stimulus that caused its formation.
Barrett's Esophagus
The Barret 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 that lines the esophagus internally is replaced by an epithelium similar to that of the duodenal walls (metaplasia of the esophageal epithelium).
To give an idea, the risk of developing an adenocarcinoma in the presence of Barrett's esophagus is estimated at 0.4 - 0.5% PER YEAR per patient. Although the Barret esophagus can be easily treated by the use of specific drugs, in this specific case the regression of metaplasia is difficult to obtain.
