Metaplasia

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Metaplasia is the replacement of one differentiated cell type with another differentiated cell type. An example is the condition synovial chondromatosis where cells of the synovial membrane undergo metaplasia to become cartilage-producing chondrocytes. Metaplasia is not synonymous with dysplasia and is not considered carcinogenesis.

Metaplasia causes precursor cells to change their cell fate, and does not change existing differentiated cells.

Metaplasia is reversible and usually occurs in response to chronic irritation and inflammation and allows for substitution of cells that are better able to survive under circumstances in which a more fragile cell type might succumb. Usually harmless in itself, metaplasia can affect the lining of various organs, such as the bronchi (airways) and bladder. Metaplasia of the cervix, which occurs in cervical erosion, can be detected by a cervical smear test.

The medical significance of metaplasia, is that cells may progress from metaplasia, to develop dysplasia, and then cancer. This occurs in many sites in the body, including the bladder, cervix, and in Barrett's esophagus. Thus where metaplasia is detected at these sites, efforts are made to remove the causative irritant, thereby decreasing the risk of progression to malignancy. The metaplastic area must be carefully monitored to ensure that dysplastic change does not begin to occur. A progression to significant dysplasia indicates that the area could need removal to prevent the development of cancer.