Here’s a good question that gets at a concept you should understand: tumor cell differentiation.

Q. I’m doing a clinical research project, and I’m supposed to record the differentiation of resected tumors per the pathology reports.  A specific report says, ” cell carcinoma with squamous differentiation.”  Is this a ‘well-differentiated’ tumor, or how do you define this in the commonly used descriptive terms?

A. There are three common types of skin cancer: basal cell carcinoma (in which the tumor cells resemble the basal layer of epithelium), squamous cell carcinoma (in which the tumor cells resemble the upper layers of epithelium), and melanoma (in which the tumor cells are trying to be melanocytes). In the image of a basal cell carcinoma above, even at this low power you can see the dark blue, palisading tumor cells that are trying their best to resemble their normal basal-layer epithelial cell counterparts.

“Basal cell carcinoma with squamous differentiation” means that you have a basal cell carcinoma in which areas of the tumor look more like the upper layers of epithelium rather than the basal layer. It sometimes happens that a tumor of one type can show “differentiation” along another cell line (e.g., a glandular tumor that shows squamous differentiation). It really doesn’t have anything to do with whether a tumor is well-differentiated or poorly-differentiated.

“Well-differentiated” and “poorly differentiated” are terms that refer to how much the tumor cells resemble their cell of origin (a well-differentiated basal cell carcinoma is composed of tumor cells that closely resemble basal cells, whereas a poorly-differentiated basal cell carcinoma is composed of tumor cells that don’t resemble basal cells very much at all). So, you could have a well-differentiated basal cell carcinoma that shows areas of squamous differentiation, or a poorly-differentiated basal cell carcinoma that shows areas of squamous differentiation. The areas of squamous differentiation are really a separate issue.

Photo credit: Wikimedia.