Carcinoma in
situ
Carcinoma in situ (CIS) is an early form of carcinoma defined
by the
absence of
invasion of
surrounding
tissues. In
other words,
the
neoplastic
cells
proliferate
in their
normal
habitat,
hence the
name 'in
situ' (Latin
for 'in its
place'). For
example,
carcinoma in
situ of the
skin, also
called
Bowen's
disease is
the
accumulation
of
neoplastic
epidermal
cells within
the
epidermis
only.
For this reason, CIS will usually not form a tumor. Rather,
the lesion
is flat (in
the skin,
cervix, etc)
or follows
the existing
architecture
of the organ
(in the
breast,
lung, etc).
Some CIS,
however,
form tumors,
for example
colon polyps
or papillary
cancer of
the
bladder.
Many forms of cancer originate from a 'carcinoma in situ'
(CIS)
lesion.
Therefore,
CIS is
considered a
precursor
that may, if
left
untreated
long enough,
transform
into a more
malignant
form of
neoplasm,
invasive
carcinoma
or, in
common
language,
"cancer".
Many doctors will not refer to 'carcinoma in situ' as
"cancer"
when
explaining a
laboratory
report to a
patient.
However,
because most
forms of CIS
have a real
potential to
turn into
invasive
carcinoma,
CIS is
usually
treated much
the same way
as a
malignant
tumor.
In the TNM classification, carinoma in situ is indicated as
TisN0M0
(Stage 0).
Dysplasia vs carcinoma in situ vs invasive carcinoma
These terms are related since they represent the three steps
of the
progression
toward
cancer:
* Dysplasia is the earliest form of pre-cancerous lesion
recognizable
in a biopsy
by a
pathologist.
Dysplasia
can be low
grade or
high grade.
The risk of
low-grade
dysplasia
transforming
into
high-grade
dysplasia
and,
eventually,
cancer is
low.
Treatment is
usually
easy.
* Carcinoma in situ is synonymous with high-grade
dysplasia in
most organs.
The risk of
transforming
into cancer
is high.
Treatment is
still
usually
easy.
* Invasive carcinoma, commonly called cancer, is the
final step
in this
sequence. It
is a disease
that, when
left
untreated,
will invade
the host
(hence its
name) and
will
probably
kill them.
It can
often, but
not always,
be treated
successfully.
Examples of
carcinomata
in situ
* Many bladder cancers are CIS.
* Cervical cancer is often predated by cervical
intraepithelial
neoplasia (CIN),
also called
dysplasia.
It is this
lesion that
is detected
with the pap
smear.
* Ductal carcinoma in situ (DCIS) of the breast is a
rather
frequent
disease with
a high
probability
of
transforming
into true
breast
cancer if
untreated.
* Bowen's disease is squamous carcinoma in situ of the
skin.
*
Colon polyps
often
contain
areas of CIS
that will
almost
always turn
into colon
cancer if
left
untreated.
* Bronchioalveolar carcinoma of the lung is the only form
of CIS that
can kill,
because it
fills the
lungs and
prevents
breathing.
Thus, it is
malignant,
but not
invasive.
For this
reason, this
unusual form
of carcinoma
is seen as
CIS by
pathologists,
not by
oncologists
or surgeons.
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