Differences between Benign and Malignant Tumors

by Richard Mitchell, MD, PhD

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    00:01 All right. That big brush on the right-hand side, is to indicate that, I’m going to be painting here with a very broad brush.

    00:10 Everything I tell you, I’m lying, there are some exceptions to everything I’m going to say, concerning whether a tumor is benign or malignant and that's part of the job of the pathologist, to be able to sort those things out.

    00:25 But in general, as a student and trying to learn your way through cancer, these at least give you some signposts along the way, so, you can kind of compartmentalize, what you think is benign versus malignant.

    00:38 Okay, broad brush got that.

    00:41 Benign tumors are usually small, there are exceptions, but they're usually small.

    00:46 They're usually encapsulated, meaning they grow so slowly, that the connective tissue around it just kind of forms a capsule and they don't tend to invade, they just expand as they grow slowly.

    00:59 There are no metastasis, typically in benign tumors.

    01:03 However just as an exception, there is an entity known as a benign metastasizing leiomyoma, that's a smooth muscle cell tumor of the uterus, that can metastasize, it's still considered benign.

    01:16 So, as I'm saying this there are exceptions to everything, but in general, benign tumors don't metastasize, they tend to be very well differentiated, they look like the cell type from which they are derived.

    01:27 They have a very characteristic typical organization, that looks like normal tissue, in that location, it's just an expansion a proliferation.

    01:36 They're typically slow growing, in fact, that's how we get them to be encapsulated and it's uncommon to see a high mitotic index, to see commonly mitoses, they're usually rarely seen in benign tumors and they're usually normal.

    01:52 So, just meaning that there's a bipolar mitosis, we're not doing something funky like going in three directions.

    01:59 Okay. On to the malignant side.

    02:02 Again, broad brush because there are some very small, very malignant tumors and melanomas for example can be very sneaky that way.

    02:11 But in general, malignant tumors are going to be larger, that's because they proliferate more.

    02:17 They tend to be infiltrative, they will invade beyond basement membrane into blood vessels and other things, so, they tend to be infiltrative invasive.

    02:26 Again, there are exceptions.

    02:28 They tend, in their end stage, to be metastasizing, but there are some tumors, that almost never metastasize, so basal cell carcinomas, it is reportable, if you have a metastasizing basal cell carcinoma of the skin.

    02:44 But in general, malignancy is associated with metastasis.

    02:48 They tend to be poorly differentiated, so, a malignant cell goes bad, it really doesn't care, to do all the specialized things that the original cell did, so, if it was a normal colonic epithelial cell, that was normally responsible for making mucus or for absorbing water, the tumor cell says, “No I'm only interested in growing,” so, they tend to lose those other normal functional activities and they become very poorly differentiated.

    03:17 They typically have an atypical structure, So, you cannot always tell what's up and what's down in malignancy, whereas in a benign tumor, you can say, “Yeah, that's kind of inside that's outside” and there's a recognizable structure, not so in malignancy.

    03:33 They tend to be rapidly growing and that's why, they tend to be found when they're larger, but they have a high mitotic index.

    03:41 They are very frequent therefore, very frequent mitosis, many of which will be abnormal, because as the tumor acquires more and more mutations and as it continues to grow and if there isn't an activation or reactivation of telomerase, then we can get abnormal breaks.

    03:59 You will often see tripolar mitosis, not a bipolar mitosis.

    04:03 But tripolar it looks like a Mercedes-Benz sign, we call that the Mercedes-Benz sign.

    04:10 Okay. So, frequently they will have multiple and abnormal mitosis.

    04:16 Malignant tumors, tend to outgrow their blood supply, actually, what they're doing is they are getting so big, they're compressing their blood supply and therefore, causing ischemic necrosis and then subsequent bleeding.

    04:32 So, we'll see hemorrhage and necrosis is also characteristics of malignant cells.

    04:36 Okay, broad brush and there are exceptions to every single one of these.

    04:42 But we'll play the game here and at least give you a framework for thinking about it.

    04:47 So, this is a benign lipoma, this was actually found in autopsy, it totally non-pathologic, you can see that it looks kind of like fat, it's a little globular fat, it's actually sitting there in the middle of the intestine and the mucosa around that is completely normal.

    05:06 But we have this little circumscribed, well-circumscribed, encapsulated growth of adipocytes, that made this lipoma a benign fat cell derived tumor.

    05:19 The appearance is consistent in uniform throughout, there is no hemorrhage, there's no necrosis, there's no abnormal structure at all.

    05:26 It's usually, if we find these at surgery, easily shelled out and they don't recur.

    05:32 Okay, again kind of broad stroke characteristics of a benign tumor.

    05:37 In comparison, this is a malignant tumor of the same lineage, so, it was originally a fat cell and now it is be turned into a liposarcoma, it is substantially larger, this is a surgical resection specimen.

    05:53 Just to give you a sense of scale, that kind of horseshoe shaped, red orange thing in the upper left-hand corner of the tumor mass, that's actually a portion of kidney, that had to be resected with the tumor, okay.

    06:07 The rest of that white tan irregularly nodular kind of material, that's all malignancy.

    06:14 It is deeply infiltrative, it's very poorly circumscribed, although we have carved it out or not me, but the surgeon has carved it out we've probably left tumor behind, that's in the patient.

    06:26 It has a very heterogeneous appearance, with focal areas of hemorrhage and necrosis, so, the areas that are firm and white are viable tumor, but there are areas of cavitation, that look kind of gray and black and or hemorrhagic, that look a little bit red, those are areas, where we've had tumor necrosis.

    06:47 And if we're going to be successful in trying to get rid of this surgically, we're going to have to remove huge margins around it, because the tumor is microscopically deeply invasive as well.

    07:00 Okay. So, we have the lipoma benign, liposarcoma clearly malignant.

    About the Lecture

    The lecture Differences between Benign and Malignant Tumors by Richard Mitchell, MD, PhD is from the course Surgical Pathology of Tumors.

    Included Quiz Questions

    1. They don't metastasize.
    2. They are not encapsulated.
    3. They can easily spread to other organs.
    4. They grow very fast.
    5. They are not organized like normal tissue.
    1. They are poorly differentiated and rapidly growing.
    2. They are small and noninvasive.
    3. They never metastasize.
    4. They have an organized structure, like normal tissue.
    5. They have low mitotic activity.
    1. They outgrow their blood supply and compress their blood vessels.
    2. They are tightly encapsulated.
    3. Their blood vessels grow independently.
    4. They compress lymphatic vessels.
    5. They have low mitotic activity.

    Author of lecture Differences between Benign and Malignant Tumors

     Richard Mitchell, MD, PhD

    Richard Mitchell, MD, PhD

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