Here are two words that can cause some serious headaches for pathology students: differentiation and dysplasia.
Both terms are graded on a scale. Cells can be anywhere from well-differentiated (pretty normal looking, and resembling the cells from which they originated) all the way down to poorly differentiated (“bad” looking, and not really resembling the cells from which they originated at all) or even anaplastic (which means that they don’t look anything at all like the cells from which they originated). Similarly, dysplasia is graded on a mild – moderate – severe scale.
The problem arises when you start talking about the actual characteristics of poorly-differentiated and severely dysplastic cells. Both types of cells have a lot in common:
- Pleomorphism (the cells and nuclei vary a lot in size and shape)
- Abnormal looking nuclei (really big nuclei, or nuclei with dark, “hyperchromatic” chromatin, or nucleoli)
- Lots of mitoses, and some abnormal mitoses (especially tripolar ones)
- Loss of architectural orientation (the cells are basically in a state of anarchy: they pile up on each other, they don’t respect their neighbor’s boundaries, and they don’t arrange themselves in the nice regular way that normal cells do).
So…what’s the deal? It seems like both concepts (differentiation and dysplasia) are talking about the same thing: the degree of abnormality or “ugliness” in a particular group of cells. So why have two words? Is this just some masochistic pathology terminology aimed at making us miserable?
It turns out that while the two terms/concepts are indeed getting at the same idea (how “ugly” the cells look), you use the terms in totally different contexts.
Differentiation is only used when talking about neoplastic cells. You would never say, “wow, that section of normal liver is really well-differentiated.” It’s only used to describe tumor cells, period. Also, you can use the concept of differentiation to describe tumor cells of any origin – epithelial, mesenchymal, whatever.
Dysplasia, on the other hand, is only used when talking about non-neoplastic cells – it’s never used to describe neoplastic cells. Also, you only use the word dysplasia when you’re talking about epithelial cells.
The classic example for illustrating dysplasia is cervical pap smears and biopsies. One good thing about cervical cancer is that it is always preceded by dysplastic changes. So the epithelial cells don’t just one day turn into malignant cells: they go through long stages of mild, moderate, and severe dysplasia.
It’s really important to know this, because you can catch cervical carcinomas before they even become carcinomas. If you see an area of severe dysplasia, you can remove those cells and thereby prevent carcinoma from developing in that area. You can see a pretty clear demarcation in the photo above between dysplastic cells (on the left) and normal cervical squamous epithelium (on the right).
So to summarize:
1. Both dysplasia and differentiation are words that get at the same concept: the degree to which cells look abnormal or “ugly.”
2. You only use “differentiation” when you’re talking about neoplastic cells (and they can be neoplastic cells of any type – epithelial or otherwise).
3. You only use “dysplasia” when you’re talking about non-neoplastic cells (and they have to be epithelial cells).