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.
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.
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.
Okay, broad brush got that.
Benign tumors are usually
small, there are exceptions,
but they're usually small.
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.
There are no metastasis,
typically in benign tumors.
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.
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.
They have a very characteristic
that looks like normal tissue, in that location,
it's just an expansion a proliferation.
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.
So, just meaning that there's a bipolar mitosis,
we're not doing something funky
like going in three directions.
Okay. On to the malignant side.
Again, broad brush because
there are some very small,
very malignant tumors
and melanomas for example
can be very sneaky that way.
But in general, malignant
tumors are going to be larger,
that's because they proliferate more.
They tend to be infiltrative, they
will invade beyond basement membrane
into blood vessels and other things,
so, they tend to be infiltrative invasive.
Again, there are exceptions.
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.
But in general, malignancy is
associated with metastasis.
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.
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.
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.
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.
You will often see tripolar mitosis,
not a bipolar mitosis.
But tripolar it looks like a Mercedes-Benz sign,
we call that the Mercedes-Benz sign.
Okay. So, frequently they will
have multiple and abnormal mitosis.
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.
So, we'll see hemorrhage and necrosis is
also characteristics of malignant cells.
Okay, broad brush and there are
exceptions to every single one of these.
But we'll play the game here and at least
give you a framework for thinking about it.
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.
But we have this little circumscribed,
growth of adipocytes,
that made this lipoma a
benign fat cell derived tumor.
The appearance is consistent
in uniform throughout,
there is no hemorrhage, there's no necrosis,
there's no abnormal structure at all.
It's usually, if we find these at surgery,
easily shelled out and they don't recur.
Okay, again kind of broad stroke
characteristics of a benign tumor.
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.
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.
The rest of that white tan
irregularly nodular kind of material,
that's all malignancy.
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.
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.
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.
Okay. So, we have the lipoma benign,
liposarcoma clearly malignant.