Q. When a squamous cell carcinoma is designated as “poorly differentiated”, what other parameters/tests are performed to determine the tissue of origin?
A. Differentiation, for those of you who have just joined us, is a quality of tumors that has to do with how  much the tumor cells resemble their tissue of origin. Well-differentiated tumors are composed of cells that closely resemble their tissue of origin, whereas poorly-differentiated tumors are composed of cells that have little resemblance to their tissue of origin. Anaplastic tumors are the least differentiated of all: they show no resemblance to their tissue of origin.
This concept is important for a couple reasons. First, the degree of differentiation of a tumor often has a bearing on prognosis. Well-differentiated tumors generally carry a better prognosis than poorly differentiated tumors. Second, when a tumor is totally undifferentiated (anaplastic), you have to resort to special tests in order to figure out its origin (is it a squamous cell carcinoma, an adenocarcinoma, a lymphoma, a sarcoma, etc.).
Back to our question: when you have a poorly-differentiated squamous cell carcinoma, how do you know it’s a squamous cell carcinoma (as opposed to an adenocarcinoma, for example)? If the tumor is poorly-differentiated, that means there are still some morphologic features (albeit few) that reveal the squamous nature of the tumor. If you look carefully, you should be able to find some of these features, which would then point you towards the diagnosis of squamous cell carcinoma.
Two clear-cut features of squamous cell carcinoma are intercellular bridging and keratin pearls (there are other, “softer” features indicating a squamous cell origin, but we’ll focus on the more definitive features). Intercellular bridging is a term describing the special connection between the epithelial cells of squamous epithelium (it’s not present in glandular epithelium). By light microscopy, you can see little horizontal hair-like connections between the epithelial cells in both normal squamous epithelium and in malignant squamous epithelium. Look closely between the epithelial cells in the above image of a squamous cell carcinoma. See the little connections between the cells (they look like little zippers connecting the cells)? Those are intercellular bridges.
Keratin pearls are whorl-shaped accumulations of keratin made by malignant squamous cells. In normal squamous epithelium, keratin lies in a nice flat layer on the epithelial surface. In malignant squamous epithelium, the tumor cells can grow in any direction they want, and so the keratin they produce often gets trapped inside the tumor, forming pink, glassy, spherical masses. Sometimes the keratin even gets trapped within the tumor cells themselves.
So, if you have a tumor that you think might be a squamous cell carcinoma, but the cells aren’t showing clear squamous cell differentiation, look closely for epithelial bridging and keratin pearls. If you find either of these, it’s a good bet that you’re dealing with a squamous cell carcinoma. There are other little clues that point towards other types of tumors (like adenocarcinoma, or melanoma, or sarcoma), but that’s for another post.
Sometimes, you’ll get a tumor that shows no defining morphologic features whatsoever – no interepithelial bridging, no keratin pearls, no signs of differentiation along any other cell line. In these tumors (which would be described as “anaplastic”), you need to use a secret weapon to figure out what the cells are: immunohistochemistry. In this technique, you use a reagent consisting of antibodies against specific components of cells (there are lots of these specific components: squamous cells have cytokeratin in them, muscle cells have actin in them, etc.). These antibodies are bound to a substance that appears brown under the microscope. The concept is simple: you apply the reagent to the tissue in question, allow it to bind to the cells, then wash off the excess reagent and look at it under the microscope. If the tumor cells appear brown, that means they possess whatever antigen the antibodies in your reagent are directed against, and that information can help you figure out what type of cells your tumor contains.
So, if you have an anaplastic tumor, you might choose to apply immunohistochemical stains for cytokeratin, actin, and CD45 (an antigen present on lymphoid cells). If the cytokeratin stain comes back positive (brown), and the actin and CD45 stains come back negative, the tumor is most likely a squamous cell carcinoma. There are tons of immunohistochemical stains for all different types of cells. Generally, these stains are pretty specific for one cell line, but it’s not always totally straightforward. Some tumors stain positive for markers from cell lines other than their cell of origin, and some tumors show only weak staining with the stains that are supposed to be nice and positive. So you really need to use a panel of a bunch of different stains to make the best diagnosis.
The bottom line, then, if you have an undifferentiated appearing tumor: look for little morphologic clues (like keratin pearls) first. If you see few or no clues, then your next step is immunohistochemical staining, which will almost always reveal the origin of the tumor. If that doesn’t work, there are still other tests you can do – like cytogenetics or molecular diagnostics – and we’ll talk about those in future posts.
Photo credit: AFIP
http://commons.wikimedia.org/wiki/File:Well_differentiated_squamous_cell_carcinoma.jpg
Wow! This post is very helpful! I have a a few questions though!
Question 1: You wrote, “In malignant squamous epithelium, the tumor cells can grow in any direction they want, and so the keratin they produce often gets trapped inside the tumor….”
Exactly how does this growth in all direction cause the keratin they produce to get trapped inside the tumor.
Question #2: By tumor you mean general locale (vicinity) of increased cell multiplication or are the abnormally dividing cells contained in some sort of encasing? And if there is an encasing, how is it created?
Question #3 What is the benefit of discovering the origin organ/gland/etc,. of a well differentiated tumor as far as treatment is concerned?
Question #3 should read:
What is the benefit of discovering the origin organ/gland/etc,. of a UNDIFFERENTIATED tumor as far as treatment is concerned?
Great questions!
Regarding question 1: Squamous epithelial cells normally grow in an organized, directional fashion, with the basal layer at the bottom, and keratinocytes in layers up until the very top, where keratin is present. Malignant squamous epithelial cells don’t respect normal architecture. They don’t have a nice, orderly, layered maturation like benign epithelium; instead, they grow in nests and sheets. If there are keratin producing cells present, they won’t necessarily layer out only at the surface of the tumor – they’ll be scattered here and there throughout the tumor nests – so keratin will just accumulate wherever it is produced (often in little “pearls” scattered throughout the tumor).
Regarding question 2: A tumor is a collection of neoplastic cells (which, as you rightly note, usually divide more frequently than their normal, non-neoplastic counterparts). Some tumors are enclosed in a casing (usually called a capsule), which is derived from the normal extracellular matrix of the tissue surrounding the tumor. When the tumor grows, it presses on the normal surrounding parenchymal cells. The parenchymal cells undergo atrophy, but the extracellular matrix remains and is compressed into a thin rim of connective tissue. Benign tumors are often encapsulated; malignant tumors usually are not.
Regarding question 3: It’s important to try to figure out the origin of an undifferentiated tumor (or any tumor, for that matter), because treatment is different for different tumors. Lymphomas, for example, are treated very differently than breast carcinomas, which are treated differently than melanomas. If a patient has an undifferentiated tumor with multiple metastases, the prognosis is likely to be grim, with the chances of cure being pretty low. Treating the patient with the appropriate chemotherapy provides the best chance for extending the patient’s survival.
Great! Do you have something about Skill Cell Basal Carcinoma?
Yep – I have posts on basal cell carcinoma here and here.
Hi Dr Krafts,
I sent you an email a few minutes ago with a question and I am just now reading this article. So I am looking at my pathology report from my thyroid biopsy and it says moderately to poorly differentiated squamous cell carcinoma. The stain results say this
pancytokeratin: strongly positive
cytokeratin 5/6: strongly positive
carcinoembryonic antigen: negative
chromogranin: negative
TTF-1: neg
S-100 neg
Mart-1 neg
Do these stain results rule out or confirm anaplastic?
I just got these results yesterday and I see a head and neck oncologist tomorrow. I was dreading anaplastic thyroid this whole weekend.
Thanks,
Charlene
I’m so sorry to hear about your tumor. I can understand why you’re worried about anaplastic thyroid carcinoma. Here’s what the markers say about primary squamous vs. anaplastic carcinoma.
pancytokeratin: strongly positive
cytokeratin 5/6: strongly positive
Cytokeratins tend to be positive in primary squamous cell carcinoma of the thyroid. There aren’t a ton of studies to evaluate – but in general, cytokeratin positivity is seen in squamous cell carcinomas. Cytokeratin is usually negative in anaplastic carcinoma.
carcinoembryonic antigen: negative
CEA is negative in squamous cell carcinoma. I don’t see it even listed for anaplastic carcinoma, so I am assuming it is negative in that tumor as well.
chromogranin: negative
I don’t see studies listing chromogranin staining in either tumor. Chromogranin is a stain that is positive in some endocrine tumors – I would expect it to be negative in both squamous and anaplastic carcinoma.
TTF-1: neg
TTF-1 can be positive or negative in primary squamous cell carcinoma of the thyroid (there are too few studies to make a generalization either way). TTF-1 is positive in about 22% of anaplastic carcinomas.
S-100 neg
S-100 is a stain that is positive in neural tumors. It is not listed in studies of squamous carcinoma (which probably means it’s negative). It is positive in most anaplastic carcinomas, for some reason.
Mart-1 neg
Mart-1 is a stain that’s positive in melanomas. I don’t see it listed for squamous cell carcinomas. It is listed as negative in anaplastic carcinomas.
Taken together, these stains point more towards squamous cell carcinoma than anaplastic. The cytokeratins are positive (which goes with squamous, and not with anaplastic), and the S-100 is negative (it would most likely be positive if the tumor were anaplastic). The other markers don’t really help one way or the other.
These stains, together with the pathologist’s comments, indicate that the tumor is squamous and not anaplastic. I hope that helps! Let me know if you have other questions after your appointment tomorrow. My thoughts are with you…
I love you man, awesome explanation, preparing for squamous cell carcinoma presentation tomorrow and your articles are a life saver 😀
Glad you found something useful! Good luck on your squamous cell carcinoma presentation!
If in a given section, all the features of well, moderate and poorly differentiated oral squamous cell carcinoma is seen then on what basis grading can be given?
You grade it on the highest grade present. You might mention in the report that there are several different areas present – but the final grade is made on the highest grade of tumor seen.