Veterinary Voice, October 2012 – Anal Sac Adenocarcinoma; Not Always a Pain in the Rear

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October 2012, Issue 48


Hope you have a safe &

HAPPY HALLOWEEN!

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From Aspen Meadow Veterinary Specialists


AMVS Event Updates!

AECC & AMVS’s CE on October 25th had a
great turn out, We hope that those of you that attended had a great
time and learned a lot about how to treat common toxicity poisoning and
look forward to seeing you all at our CE’s in the winter. 


Upcoming Events!

pageimage_1091_112190_2_1AMVS
will be taking family and pet holiday portraits with Santa, at our
facility in Longmont, CO so keep your eyes open for more information to
be announced…

You can also find information about our upcoming events by checking out our facebook page.

Simply click on the link below.

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Anal Sac Adenocarcinoma;

Not Always a Pain in the Rear

By: Jim Perry, DVM, PhD, DACVIM

Oncologist; Orthopedic Surgical Resident

Practice Points:

1. Anal sac adenocarcinoma is a top differential in any animal presenting with hypercalcemia

2. Metastasis is present at the time of diagnosis in greater than 50%
of animals with anal sac adenocarcinoma; staging should included blood
work, UA, thoracic radiographs and abdominal ultrasound.

3. Surgery is the mainstay of treatment even when metastatic disease is evident within the local lymph nodes.

4. Carboplatin, doxorubicin and mitoxantrone can be considered
following surgery, but no controlled studies have proven efficacy of
adjuvant chemotherapy.

5. Palladia has recently been described to have a clinical benefit for the treatment of gross disease.

The anal glands in dogs and cats are small glands found next to the
rectum and are lined with secretory apocrine gland cells. Tumors
associated with these cells within the anal sac are commonly called
apocrine gland adenocarcinoma or anal sac adenocarcinoma (ASACA). This
type of tumor is relatively uncommon, but highly malignant in dogs. This
is in contrast to the usually benign “perianal” or “hepatoid” gland
adenomas that primarily occur in intact male dogs. ASACA often occurs
unilaterally, but several case reports have described bilateral disease.
In addition to being very locally aggressive, up to 50% of these tumors
show evidence of spreading to other sites within the body at the time
of diagnosis. The most common sites for these tumors to metastasize
include the local lymph nodes (medial iliac/hypogastric LN), liver, and
lungs. 

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Left anal sac adenocarcinoma

9yr old male Akita mix

The average age of diagnosis of ASACA is
10 years old. Greater than 25% of animals presenting with ASACA have
hypercalcemia associated with the paraneoplastic production of a
parathyroid-related protein (PTHrp). If hypercalcemia is present, this
should be treated prior to surgery using IV non-calcium containing
balanced crystalloid fluids, Lasix, bisphosphonates (Pamidronate:
1-2mg/kg IV diluted in 0.9% NaCl to be administered over 2 hours) or
steroids (dexamethasoneSP at 0.7mg/kg IV or prednisone at 1-2mg/kg PO
q24). The latter should only be used if diseases such as lymphoma have
been ruled out. The use of calcitonin is discussed in many texts, but is
rarely needed in addition to the more available and cost effective
treatment modalities listed above.

The mainstay of treatment for anal sac
adenocarcinoma is surgery. Prior to surgery however, staging with blood
work, thoracic radiographs, and abdominal ultrasound should be performed
to determine the most appropriate treatment plan. While surgical
removal provides the most significant increase in survival time, even in
the presence of sublumbar lymph node metastasis, adjunctive
chemotherapy and/or radiation therapy are often considered to further
benefit the patient’s disease free interval and survival time.

Negative prognostic factors for dogs with
ASACA include evidence of metastasis, hypercalcemia, and tumor size at
the time of surgery. The median survival time for dogs treated with
surgery for ASACA with lymph node metastasis is 20 months (with primary
tumor resection and sublumbar lymph node extirpation) and 30 months for
dogs with tumor localized to the anal sac without evidence of metastatic
disease. Patients with evidence of pulmonary metastases have even
shorter survival times-only 7 months in one study. With regards to
calcium levels, dogs presenting with hypercalcemia had significantly
shorter survival (median, 9 months), compared with those that were
normocalcemic (median, 20 months). Finally, dogs with primary tumors ≥
10 cm3 had significantly shorter survival (median, 10 months) than dogs
with tumors ≤ 10 cm3 (median, 20 months) following surgery.

Current chemotherapy recommendations
included carboplatin, doxorubicin, and/or mitoxantrone. Since
carboplatin and doxorubicin are both radiation sensitizing agents,
mitoxantrone is often used if radiation therapy is being included in the
protocol. Radiation therapy, when used, often includes 18-20 fractions,
administered M-F. Side effects of radiation therapy to the sublumbar
and perianal region can be severe, and therefore it is not currently
recommended.

There is also recent evidence showing
efficacy of tyrosine kinase inhibitors (Palladia) for the treatment of
non-resectable ASACA or when surgery is otherwise not an option. In a
recent study looking at dogs with gross disease, a clinical benefit was
appreciated in 87% of the dogs treated with Palladia (25% partial
responses and 62% stable disease). The median duration of a partial
response in this study was 22 weeks and stable disease was 30.5 weeks.

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right anal sac carcinoma

9yr old male Bassett Hound

Currently at AMVS, the diagnostic and
treatment recommendation for ASACA includes full staging with CBC,
Chemistry, UA, thoracic radiographs and abdominal ultrasound. If the
disease is localized to the anal glands with or without regional
abdominal lymph node involvement, surgical removal of the primary tumor
and lymph nodes is the mainstay of treatment. Adjuvant chemotherapy (6
doses of carboplatin) is recommended for large primary tumors (>10
cm3) or if metastatic disease is noted. If surgery or traditional
chemotherapy is not elected or if distant metastatic disease is present,
then Palladia is recommended with the goal in mind to delay progression
as long as possible while maintaining a good quality of life. If
hypercalcemia is present at any phase of the disease process, additional
supportive therapies such as steroids or bisphosphonates are combined
with the above treatment recommendations.

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Thank you for your continued support!

-Aspen Meadow Veterinary Specialists

104 S. Main Street

Longmont, CO 80501

303-678-8844 (p)

303-678-8855 (f)

info@AspenMeadowVet.com

www.AspenMeadowVet.com

 

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