Metaplasia, dysplasia, anaplasia
What it means
Metaplasia: reversible change of one differentiated cell type to another (Barrett's: squamous→columnar; smoker's bronchial columnar→squamous). Dysplasia: disordered growth with cytological/architectural atypia — pre-malignant, reversible if the stimulus is removed. Anaplasia: complete loss of differentiation — a hallmark of malignancy.
Worked example
Columnar (intestinal) metaplasia of the lower oesophagus from chronic acid reflux = Barrett's oesophagus (a pre-malignant change).
In the exam
Chronic acid reflux causes the distal oesophageal squamous epithelium to be replaced by columnar (intestinal-type) epithelium.
What settles it
Metaplasia (reversible cell-type switch) → dysplasia (atypia, pre-malignant) → anaplasia/carcinoma (malignant, irreversible).
Classically confused with
Benign vs malignant neoplasia
Source: StatPearls