Anal cancer
Anal cancer
is a type of
cancer which
arises from
the anus,
the distal
orifice of
the
gastrointestinal
tract. It is
a distinct
entity from
the more
common
colorectal
cancer. The
etiology,
risk
factors,
clinical
progression,
staging, and
treatment
are all
different.
Anal cancer
is typically
a squamous
cell
carcinoma
that arises
near the
squamocolumnar
junction.
Epidemiology
Incidence
* In
women and
men who do
not engage
in anal
intercourse
with other
men -
0.9/100,000
* In HIV
negative men
who engage
in anal
intercourse
with other
men -
35/100,000
* In HIV
positive men
who engage
in anal
intercourse
with other
men -
(estimated)
60-70/100,000
Anal cancer
is uncommon
and accounts
for only 4%
of all
cancers of
the lower
alimentary
tract. There
are
estimated to
be 4,650 new
cases and
690 deaths
from anal
cancer in
the United
States in
2007.
Risk
factors
* Human
papillomavirus
(HPV)
infection:
An
examination
of squamous
cell
carcinoma
tumor
tissues from
patients in
Denmark and
Sweden
showed a
high
proportion
of anal
cancers to
be positive
for the
types of HPV
that are
also
associated
with high
risk of
cervical
cancer (90%
of the
tumors from
women, 100%
of the
tumors from
homosexual
men, and 58%
of tumors
from
heterosexual
men). In
another
study done,
high-risk
types of HPV,
notably
HPV-16, were
detected in
84 percent
of anal
cancer
specimens
examined.
* Sexual
activity:
Having
multiple sex
partners or
having anal
sex, due to
the
increased
risk of
exposure to
the HPV
virus.
*
Smoking:
Current
smokers are
several
times more
likely to
develop anal
cancer
compared
with
nonsmokers.
*
Immunosuppression,
which is
often
associated
with HIV
infection.
Prevention
Since many,
if not most,
anal cancers
derive from
Human
Papilloma
Virus
infections,
and since
the HPV
vaccine
prevents
infection by
several
strains of
the virus,
scientists
surmise that
HPV
vaccination
will prevent
anal cancer.
Screening
Anal pap
smears
similar to
those used
in cervical
cancer
screening
have been
studied
experimentally
for early
detection of
anal cancer
in high-risk
individuals.
Treatment
Localized
disease
Anal cancer
is most
effectively
treated with
surgery, and
in early
stage
disease
(i.e.,
localized
cancer of
the anus
without
metastasis
to the
inguinal
lymph
nodes),
surgery is
often
curative.
The
difficulty
with surgery
has been the
necessity of
removing the
anal
sphincter,
with
concomitant
fecal
incontinence.
For this
reason, many
patients
with anal
cancer have
required
permanent
colostomies.
In more
recent
years,
physicians
have
employed a
combination
strategy
including
chemotherapy
and
radiation
treatments
to reduce
the
necessity of
debilitating
surgery.
This
"combined
modality"
approach has
led to the
increased
preservation
of an intact
anal
sphincter,
and
therefore
improved
quality of
life after
definitive
treatment.
Survival and
cure rates
are
excellent,
and many
patients are
left with a
functional
sphincter.
Some
patients
have fecal
incontinence
after
combined
chemotherapy
and
radiation.
Biopsies to
document
disease
regression
after
chemotherapy
and
radiation
were
commonly
advised, but
are not as
frequent any
longer.
Current
chemotherapy
active in
anal cancer
includes
cisplatin
and 5-FU;
mitomycin
has also
been used,
but is
associated
with
increased
toxicity.
Metastatic
or recurrent
disease
Up to 10% of
patients
treated for
anal cancer
will develop
distant
metastatic
disease.
Metastatic
or recurrent
anal cancer
is difficult
to treat,
and usually
requires
chemotherapy.
Radiation is
also
employed to
palliate
specific
locations of
disease that
may be
causing
symptoms.
Chemotherapy
commonly
used is
similar to
other
squamous
cell
epithelial
neoplasms,
such as
platinum
analogues,
anthracyclines
such as
doxorubicin,
and
antimetabolites
such as 5-FU
and
capecitabine.
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