Dysplasia and Carcinoma in Situ

Expansion

The sequence

1. Normal epithelium
2. Metaplasia - a reversible change to another differentiated cell type, adaptive
3. Dysplasia - disordered growth with cytological atypia, graded low or high. Still potentially reversible
4. Carcinoma in situ - full thickness dysplasia with all the cytological features of malignancy, but confined by the basement membrane
5. Invasive carcinoma - the basement membrane is breached

“Carcinoma in situ cannot metastasise, because metastasis requires invasion.” That single fact is why detecting it is the purpose of screening, and why it is curable by local treatment.

Features of dysplasia: increased nuclear to cytoplasmic ratio, hyperchromasia, pleomorphism, increased and abnormal mitoses, loss of polarity and loss of maturation towards the surface.

Examples: cervical intraepithelial neoplasia (CIN), Barrett’s dysplasia, colonic adenoma, ductal carcinoma in situ of the breast, and actinic keratosis in skin.

The whole logic of screening programmes rests on this sequence: it is long enough to detect an intervening stage, and treating that stage prevents the cancer, which is why cervical and bowel screening work.