So, I don't quite understand what the term carcinoma in situ means - I took a look in Robbins and the text says that it refers to a situation when there are dysplastic changes that involve the full thickness of an epithelium, but are not invasive. Doesn't the term carcinoma imply malignancy, which itself implies invasion/ spread? So, since carcinoma in situ is not invasive, does this mean it is a technically a benign neoplasm (despite the carcinoma name)? Also, based on the definition in Robbins, it seems that this term is only used to distinguish between high and low grade dysplasia for a straitified squamous epithelium - b/c for any other epithelium type (ex. simple columnar), full thickness dysplasia would be the same thing as plain old dysplasia since there would only be one cell layer...
X = Cancer cells
O = Happy Cells
_ = Basement membrane
OOOOOOO
OOOOOOO Normal Epithelium "yay!"
OOOOOOO
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XXXXXXX
XXXXXXX Carcinoma in Situ "uh oh"
XXXXXXX
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XXXXXXX
XXXXXXX Invasive Carcinoma "cancer'd!"
XXXXXXX
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X------------
XXXXXX
XXX..XX..XX
XX...XX.X.X..X..X..X..XX.X
now here's a real kicker... There are different degrees of dysplasia. Lets look at the nomenclature for squamous cell carcinoma
XXXXXOO
OOOOOO CIN I, "meh, mild dysplasia"
OOOOOO
OOOOOO
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XXXXXOO
XXXXXOO CIN II "meh, moderate dysplasia"
OOOOOO
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XXXXXXX
XXXXXXX Carcinoma in Situ, CIN III "ooh, severe dysplasia"
XXXXXXX
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So carcinoma in situ is
NOT "benign" because if you don't do anythign about it, it will eventually progress.
CIN 1 --> CIN 2 --> Carcinoma in Situ = CIN 3 --> Invasive carcinoma.
If you've followed this so far, lets keep going. Once its invasive, it depends on spread. If its all over the body (
mets) then its
stage 4. If its just a little invaded (and this differs from cancer to cancer on "how much invasion does it take to upstage"), its stage 2 or 3.
Carcinoma in situ by defintion is
Stage 1, that is, limited to the tissue without invasion through the basement membrane.
How does it get into the rest of the body? Either by
local invasion (the picture i showed) or by
lymph or
blood spread. What is right on the other side of that basement membrane? Yep. Blood vessels and lymph. Also neural tissue, which is why reports will usually see no vascular or perineural involvement.
Think of the
basement membrane as the flood gate. You've got the mighty mississippi on one side (the cancer), and the entirety of southwest louisiana on the other (the body). If you don't get this reference, you should pay more attention to CNN. As long as the flood gates are closed (basement membrane intact) the river stays in the river. But once you open that gate up (invasion), the mississippi is going to flood everywhere. Neurons, Lymph, Blood, and then its up to you to stage, that is, find how far the cancer has gotten to determine treatment.
To get back to
benign vs not, there are tumors that will grow. And they grow alot. But a benign tumor just never invades. That's what makes it benign.
Benign = will not invade. It can get huge, steal all the person's blood, destroy organs, literally eat the person from the inside out, but its still "benign" because it wont invade.
Malignant tumors invade. Malignant tumors are those that will invade. A carcinoma in situ squamous cell carcinoma of the cervix, for example, is malignant. I suppose, much like a polyp in the colon, it could be considered "pre-malignant" because it "hasn't invaded yet." But
"premalignant" and "benign" are not the same thing. Using colon cancer as an example, a tubular pedunculated polyp is benign, as in, not precancer, so you only have to increase the screening a little. A Sessile, villous tumor with active dysplasia is premalignant, and screening is stepped up alot.
So in summary:
Benign = tumor will not invade
Malignant = tumor will invade
Premalignant = tumor hasn't invaded yet but it will
Carcinoma in Situ = tumor that hasn't invaded the basement membrane
Carcinoma in Situ = Stage 1 = curable with local resection only
Stage 2 = a little out of the basement membrane (variable per cancer)
Stage 3 = a little more out from the basement membrane (variable per cancer)
Stage 4 = Metastasis.