Q. What is the connection between dysplasia and neoplasia? I understand that dysplasia is a precancerous condition. Grades I and II are not neoplastic. But grade III dysplasia, also called carcinoma in situ, is neoplastic, right? But is it a true carcinoma, or is it not at that point malignant?
A. Dysplasia is not a neoplastic process. While it is often a precursor to neoplasia, not all cases will evolve into malignancy (e.g., mild cervical dysplasia usually does not progress to carcinoma. We watch patients who have it carefully, though, to catch those patients that do go down that path.).
Carcinoma in situ is neoplastic. The cells in carcinoma in situ have the potential to invade (and definitely will, if left alone and untreated). They have acquired enough genetic mutations to have the characteristics of malignant cells (they are able to invade, able to grow on their own without growth signals, insensitive to growth-inhibiting signals, able to metastasize, etc).
Some classification schemes equate grade III dysplasia with carcinoma in situ, while others leave carcinoma in situ in its own category at the far end of the nastiness spectrum. Personally, I prefer the latter way of looking at things, because keeps the separation between dysplasia and neoplasia intact.
The important thing to remember, no matter what semantics you choose, is that the chances of evolution into overt carcinoma rise with the degree of dysplasia. Mild dysplasia usually does not evolve into carcinoma, whereas severe dysplasia usually does.
The image above shows a portion of cervical epithelium that has undergone dysplastic change. The right hand side of the image shows normal squamous epithelium, and the left hand side of the image shows moderately dysplastic epithelium. The dysplastic epithelial cells are pleomorphic (varying in size and shape) and hyperchromatic (darkly-staining) nuclei. Their architecture is also disrupted. Instead of the nice basal layer and orderly maturation and flattening-out of cells that you see in normal epithelium, much of the epithelial thickness resembles the basal layer.