ANAL SAC ADENOCARCINOMA
The following information is simply
informational. It's intent is not to replace the advice of a
veterinarian nor to assist you in making a diagnosis
of your pet. Please consult with your own veterinary physician for
confirmation of any diagnosis. Your pets life may depend on
it.
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OVERVIEW
Anal sac adenocarcinomas are
tumors arising from the apocrine glands present on either side of
the rectum. They occur primarily in older (average 10 years) female
dogs. Dogs might have symptoms such as straining to have bowel
movements (either due to the tumor itself or due to enlarged lymph
nodes in the pelvic area), or the tumors might be found incidentally
on a routine physical examination. Sometimes dogs may have symptoms
such as increased drinking and urinating which results from very
high calcium levels in the blood (due to hormones produced by the
tumor) which in turn can affect the kidneys.
There is not much written about the tumors that
appear in the very last inch of the GI tract in pets. Each sex has
its own syndrome. Intact male dogs develop tumors of the tiny perianal glands
that surround the anus. Senior female dogs develop malignancies of
the anal sacs some of which manifest
hypercalcemia.
The last inch of the G.I. tract in pets has the potential to
develop tumors that can be fatal. If our profession continues to
educate pet guardians regarding the value of neutering male dogs,
many lives would be saved. Veterinarians can include rectal exams in
their well dog annual physical exams. The public could also request
that their pet receive a rectal exam from their vet if it is not
offered initially. Awareness is the best medicine we can offer for
this important last inch of the GI tract.
CLINICAL SIGNS IN MALE DOGS**
Half of the cases initially presented to their
local veterinarian with one large perianal mass which affected
elimination behavior. Half of the tumors were discovered by their
local vet on a routine physical exam or when the pet was presented
for another reason. Some dogs presented with several nodules around
the anus involving the sphincter muscles. Some of the tumors may be
infected, ulcerated and cause the dog to worry the area with
persistent licking and chewing the site. Generally, the dog had one or two excisional
biopsy procedures prior to the metastatic event which led them to
our
service.
Time to metastases in most cases was at least several months
and often 9-12 months following the first or second surgery. Follow up visits with rectal
palpation were variable. Dogs generally presented with a history of
tenesmus and or constipation problems. Dogs may have a history of
abnormal eliminations with ribbon-like stool or smaller than normal
size or droppings from one angle. Local recurrence was often
accompanied by the presence of a large sub-lumbar mass obstructing
the distal colon.
Some dogs present with deep sphincter recurrence along with
the sublumbar lymphadenopathy six to 9 months post initial surgery.
Panels on these dogs do not show abnormalities in calcium
levels.
Most of the dogs were suspected to have routine perianal
tumors and there is no way to tell the malignant tumors apart from
the benign ones, unless they are biopsied.
The end result to consider is that 50% recur after attempts
to control them by castration and dogs die of metastases to the
sublumbar lymph nodes. With these events in mind, I recommend a more analytical
approach and a more rigid follow up program to scout for recurrent
perianal tumors in senior male dogs.
IN FEMALE DOGS
Hypercalcemia is a tell tale marker
for anal sac carcinoma in female dogs. If the dog does not exhibit
the enlarged lymph nodes which are characteristic of lymphoma, a
search for anal sac carcinoma is indicated. Anal sac carcinomas
should be considered very aggressive from the start. Even small
tumors release cancer cells that travel forward involving the dorsal
rectal nodes, the sublumbar and illiac lymph node
chain.
Symptoms typical of hypercalcemia
are increased thirst and urine output, polydypsia and polyuria.
Renal injury is a sequelae of hypercalcemia in that calcium
precipitates lodge in the nephrons causing elevations of BUN and
Ceatinine levels.
Affected dogs must be treated for
malignant hypercalcemia with saline diuresis and monitored closely
during and post surgically. Once the primary tumor is exised, the
calcium level returns to normal. Recurrence or metastases may be
detected.
Upon recheck lab work that shows
hypercalcemia.
DIAGNOSIS/INITIAL
EVALUATION*
Initial evaluation of a dog that is suspected to have an anal sac
tumor should include a blood cell count and blood chemistries
(particularly to evaluate blood calcium and phosphorus levels and
kidney function) and ultrasound or X-ray examination of the abdomen
to look for evidence of tumor spread to the pelvic lymph nodes. Dogs
can have fairly small tumors in the anal sac and still have very
enlarged lymph nodes. Chest X-rays might also be helpful because
these tumors can also spread to the lungs.
TREATMENT***
Surgery is the first treatment
approach. If the primary tumor is amenable to surgery, it should be
removed. While this is unlikely to result in cure because these
tumors tend to spread early in the course of disease, it might
provide a significant disease-free interval with a good
quality of
life. The goals of
surgery are to minimize symptoms and to return the blood calcium to
normal if it is elevated. If the lymph nodes are enlarged, they can
be removed as well. Surgery in these areas can be technically
challenging and might require a surgical specialist. The benefits of
surgery must be weighed against the risk of complications.
Radiation therapy can be used to
control both the primary tumor and associated lymph nodes. It can be
used alone or in combination with surgery, depending on the
particular dog in question. Similarly, chemotherapy might be useful (either alone or in
combination with other treatments) in causing regression of the
tumor or delaying the progression of the disease. However, more
studies need to be done to more fully define the best treatment
protocols for this tumor. Treatment decisions are based on a
thorough evaluation of each individual case and the clinical
judgment of the oncologist and/or surgeon.
Unfortunately, regardless of
treatment, most dogs will still eventually succumb to this tumor.
For dogs treated with surgery alone, average survival times are
about 9 months, with a range of several weeks to over three years.
Some early anecdotal reports suggest that an aggressive combination
of surgery, radiation and chemotherapy might improve on these
results, but this remains to be confirmed.
ONGOING CLINICAL TRIALS FOR ANAL SAC
ADENOCARCINOMA
CLINICAL TRIAL RESULTS
|
J Am Vet Med Assoc. 2001 Dec 15;219(12):1729-31,
1708.
Omentalization of
cystic sublumbar lymph node metastases for long-term
palliation of tenesmus and dysuria in a dog with anal sac
adenocarcinoma. |
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Hoelzler MG, Bellah JR, Donofro MC.
A 13-year-old castrated male Bassett Hound was examined
because of a 2-week history of severe constipation and tenesmus.
Radiography revealed a large cystic mass in the caudal portion of
the abdomen that was compressing the urethra and obstructing the
pelvic canal. A small perianal mass was also noticed in the region
of the left anal sac. Exploratory surgery was performed, but the
mass was deemed unresectable. Instead, the mass was incised,
drained, and omentalized in an attempt to establish continuous
drainage after surgery. Cytologic evaluation of the perianal mass
was consistent with a diagnosis of anal sac adenocarcinoma.
Histologic evaluation of the abdominal mass revealed it was a lymph
node effaced by adenocarcinoma. Despite the poor prognosis for anal
sac adenocarcinoma with metastatic spread to the sublumbar lymph
nodes, tenesmus and dysuria in this dog remained palliated until the
dog's death 18 months after surgery. Omentalization was successful
in providing a continuous method of fluid drainage for this
cystopapillary abdominal tumor.
PMID: 11767923 [PubMed
- indexed for MEDLINE]
2: J Vet Intern Med. 2002
Jan-Feb;16(1):100-4
Canine anal sac adenocarcinomas: clinical
presentation and response to therapy.
Department of Veterinary Clinical Sciences,
Purdue University, West Lafayette, IN, USA. pfbvet@yahoo.com
A
retrospective study of 43 dogs with anal sac adenocarcinoma (ASAC)
was performed to characterize the clinical presentation and response
to treatment. Clinical signs at presentation varied considerably,
with signs related either to sublumbar nodal metastasis (tenesmus or
constipation) or hypercalcemia (polyuria-polydipsia and anorexia)
being the most frequent findings. At the time of presentation, 23
(53%) dogs had hypercalcemia and 34 (79%) had metastases, with the
regional lymph nodes (31 dogs, 72%) being the most common site of
metastasis. A variety of chemotherapeutic agents were administered,
with partial remission (PR) recorded in 4 of 13 (31%) dogs treated
with cisplatin and in 1 of 3 (33%) dogs treated with carboplatin.
The median survival for all dogs was 6 months (range, 2 days-41
months). There was no statistical association between the presence
of hypercalcemia and survival, although the power of the study to
detect an increase in survival of 3 months was low (.33). We
conclude that platinum chemotherapy has antitumor activity in canine
apocrine gland carcinoma and that further study of these agents is
warranted.
PMID: 11822797
[PubMed - indexed for MEDLINE]
LINKS FOR ADDITIONAL INFORMATION ON ANAL SAC
ADENOCARCINOMA
Flat Coated Retriever Society of
America
Sparky's Cancer Page
Merck Veterinary
Manual
ACKNOWLEDGMENTS
Canine Cancer Awareness gratefully
acknowledges the University of Pennsylvania Cancer Center (OncoLink) for granting us permission for
the use of the above information.
**Many thanks and acknowledgment to
Dr. Alice Villalobos, Editor-in-Cheif of the American Association of
Human Animal Bond Veterinarians; Animal Oncology
Consultation Service
Coast Pet Clinic of Hermosa Beach, Inc. for
enthusiatically granting us permission to use the above information. To
read more about the wonderful work Dr. Villalobos has done in the field of
animal oncology click
here.
***Canine Cancer Awareness gratefully acknowledges the
University of Pennsylvania Cancer Center (OncoLink) for granting us permission for the
use of the above information as it appears in their "ask the experts"
section.
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