Cellular Adaptation IV: Dysplasia and Metaplasia

Dysplasia

Dysplasia refers to abnormal changes in the size, shape, and organization of mature cells, characterized by pleomorphism, nuclear abnormalities, and increased mitotic activity. It commonly affects epithelial tissues, including the cervix, gastrointestinal tract, respiratory mucosa, and endometrium. Although it may occur alongside hyperplasia, dysplasia is not a true adaptive response but a preneoplastic change with potential to progress to cancer.

When confined above the basement membrane, it may be reversible if the underlying cause is removed. Once cells invade beyond the basement membrane, they become invasive carcinoma. Dysplasia is graded as low- or high-grade based on cellular atypia and structural disruption, guiding treatment and cancer risk assessment.

Metaplasia

Metaplasia is the reversible replacement of one mature cell type with another better suited to environmental stress. It occurs mainly in epithelial tissues and results from the reprogramming of local stem or progenitor cells under the influence of growth factors, cytokines, and extracellular signals. While initially protective, persistent injury can lead to genetic changes, progressing to dysplasia and carcinoma. Removal of the trigger may restore normal tissue.

Classic examples include respiratory metaplasia in smokers, in which ciliated columnar epithelium is replaced by stratified squamous epithelium, impairing mucociliary clearance, and Barrett esophagus, in which chronic gastroesophageal reflux prompts the replacement of squamous epithelium in the distal esophagus with intestinal-type columnar cells. Although more resistant to acid, this metaplastic change increases the risk for esophageal adenocarcinoma.