Canvas now up to date – plus a quick explanation of a quiz 3 question.

Just a quick update – all the scores for all three of our quizzes are now posted on Canvas.

I have a couple comments about quiz 3. First: please note that Quiz 3 ended up only having 10 points instead of 15 (so your score for that quiz is out of a total of 10 points).

Second: there was one question on Quiz 3 that was problematic for quite a few people because of a misleading lecture slide – so I made a grade adjustment, and I want to be sure that you understand the concept correctly.

Here’s the question:

4. When a tumor is “well-differentiated,” that means:
A. The tumor cells look very similar to their cell of origin
B. The tumor cells look very different from each other
C.  The tumor is benign
D. The tumor probably has a poor prognosis

The correct answer is A (The tumor cells look very similar to their cell of origin). “Differentiation” refers to how closely a tumor’s cells resemble their cell of origin. Well-differentiated tumors are composed of cells that closely resemble their cell of origin, whereas poorly-differentiated tumors are composed of cells that hardly resemble their cell of origin at all.

Quite a few of you answered C (The tumor is benign). That answer is incorrect – but I can see why you may have chosen that answer based on this slide (slide 8 from the Neoplasia I: Tumor Nomenclature ppt):

This slide is misleading, because it seems to be saying that benign tumors are always well-differentiated, and malignant tumors are always poorly-differentiated (which isn’t true).

What I was trying to do on this slide was to list the general characteristics of benign vs. malignant tumors (for example: benign tumors tend to grow slowly, whereas malignant tumors tend to grow quickly). And with regard to differentiation, benign tumors tend to be well-differentiated, and malignant tumors tend to be poorly differentiated. But those are just big-picture trends! In real life, benign tumors are occasionally poorly-differentiated, and malignant tumors are sometimes well-differentiated.

Back to the quiz question. Choice C is incorrect because while it’s true that benign tumors tend to be well-differentiated, you can also see well-differentiated malignant tumors too! So just because a tumor is well-differentiated, that doesn’t automatically mean it is benign. It kind of makes you think in that direction – but it’s just a general rule of thumb (not an absolute rule).

I hope that makes sense. If not, please shoot me an email and I’ll be happy to explain it further.

Given the misleading slide, I went in and added a point to the score of everyone who answered C 🙂

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