Metaplasia, Dysplasia and Carcinoma in Situ

Key points

• • These are three changes that some tissues may show on the path towards cancer, each more worrying than the last, but one does not inevitably lead to the next.
• • Metaplasia is the reversible change of one mature cell type into another that is better suited to a stress, such as the gullet lining changing to a gut-type lining in acid reflux (Barrett oesophagus).
• • Dysplasia is disordered growth with abnormal-looking cells that have not yet invaded; it is graded from mild to severe, and low-grade dysplasia may regress if the cause is removed.
• • Carcinoma in situ is severe dysplasia involving the full thickness of the surface layer, but the cells have not yet broken through the basement membrane.
• • Because carcinoma in situ has not invaded through the basement membrane, it has no capacity to metastasise at that stage, so finding it early can prevent an invasive cancer from developing.
• • Once the abnormal cells break through the basement membrane it becomes an invasive cancer that can spread, which is the key dividing line.