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Adenocarcinoma, Anal Sac 29

Adenocarcinoma, Anal Sac Client Education
Sheet
VetBooks.ir Diseases and Disorders

due to tumoral production of parathormone-
BASIC INFORMATION
related peptide (parathyroid hormone–related monitoring of serum calcium levels in
the immediate postoperative period is
Definition protein [PTHrP]). required.
Malignant neoplasm arising from apocrine • Radiation therapy
glands of the anal sac DIAGNOSIS • Various chemotherapeutic agents have been
investigated for adjuvant and palliative
Synonyms Diagnostic Overview management of anal sac adenocarcinoma
Apocrine gland adenocarcinoma, apocrine Diagnosis is based on physical exam (visualiza- in dogs, including carboplatin, cisplatin,
gland anal sac adenocarcinoma (AGASA or tion or palpation of a perineal mass) and history actinomycin-D, mitoxantrone, melphalan,
AGASACA) (tenesmus, dyschezia, signs of hypercalcemia). and toceranib phosphate (Palladia), but the
• Fine-needle aspirate cytology is useful for role of adjuvant chemotherapy in the treat-
Epidemiology differentiating neoplastic from inflammatory ment of anal sac adenocarcinoma remains
SPECIES, AGE, SEX processes. poorly defined.
Tumors occur more frequently in dogs than • Confirmation of the diagnosis requires • Hypercalcemia should resolve on surgical
cats, typically in older animals (median age, histopathology. removal of the primary tumor, but it may
9-11 years and 12 years, respectively). There persist if widespread metastases are present.
is no sex predisposition. Differential Diagnosis • In dogs with advanced disease, palliative use
• Other tumors of the anal sac (e.g., squamous of chemotherapy or radiation therapy may
GENETICS, BREED PREDISPOSITION cell carcinoma, melanoma) be indicated.
Spaniel breeds, particularly English cocker • Perianal adenoma or adenocarcinoma
spaniels • Perineal hernia Chronic Treatment
• Anal sac abscess • If metastases cause persistent hypercalcemia,
RISK FACTORS • Other cutaneous neoplasia additional therapy may be necessary (p. 491).
Neutering may increase risk, particularly for • Perineal fistula
male dogs. Possible Complications
Initial Database • Postoperative complications include tenes-
ASSOCIATED DISORDERS • CBC, serum chemistry profile, urinalysis, ± mus, hematochezia, fecal incontinence,
Paraneoplastic hypercalcemia occurs in ionized calcium incisional dehiscence, incontinence, rectal
approximately 50% of dogs with anal sac • Thoracic radiographs or thoracic CT scan prolapse, perirectal abscess, and stenosis.
adenocarcinoma. • Abdominal ultrasound or CT scan • Acute radiation complications include ery-
thema and dry or moist desquamation of
Clinical Presentation Advanced or Confirmatory Testing perineal skin and mild to moderate colitis.
HISTORY, CHIEF COMPLAINT • Fine-needle aspirate cytology of affected anal • Late radiation effects include rectal fibrosis
• Perineal irritation manifested by licking/ sac or stricture and chronic diarrhea.
biting at region, scooting, bleeding • Incisional biopsy for larger tumors to aid in • Hypocalcemia (p. 515) can occur postop-
• Dyschezia or tenesmus ± stranguria, especially planning definitive surgical resection eratively in patients with hypercalcemia
with sublumbar lymphadenopathy • Abdominal CT or MRI, including the before surgical excision of their tumors.
• If hypercalcemia present: polyuria, polydipsia, perineal region for clinical staging and surgi-
vomiting, poor appetite, weakness cal and/or radiation therapy planning PROGNOSIS & OUTCOME
• 40% of tumors are found incidentally on
routine physical exam. TREATMENT • Approximate median survival times for dogs
treated with surgery, radiation therapy, or
PHYSICAL EXAM FINDINGS Treatment Overview chemotherapy alone are 7-9, 21, and 7
• Rectal exam reveals a mass in the region of The goals of treatment are to months, respectively.
the anal gland ± palpable sublumbar lymph • Provide adequate locoregional control of • The longest reported median survival time
node enlargement. disease for anal sac adenocarcinoma is 31.4 months
• Palpable caudal abdominal mass effect in • Palliate clinical signs associated with the with a combined therapy of surgery, defini-
cases of moderate to severe sublumbar lymph primary tumor, regional metastases, and/or tive radiation therapy, and mitoxantrone
node enlargement hypercalcemia chemotherapy
• Large tumors may be visible perineally. • Negative prognostic factors include hyper-
• Tumors may be bilateral. Acute General Treatment calcemia, primary tumor size > 10 cm, and
• Surgical excision of the primary tumor is pulmonary metastases.
Etiology and Pathophysiology recommended along with removal of enlarged • The presence of iliac lymphadenopathy is
• Anal sac apocrine gland adenocarcinoma regional lymph nodes, especially when an inconsistent negative prognostic factor.
tumors arise from the apocrine glands of the causing obstruction of the pelvic canal or • Information on the outcome in cats is
walls of the anal sacs. in cases of concurrent hypercalcemia. lacking; however, a multimodal treatment
• Tumors are locally invasive and have a high ○ Approximately one-half of the anal approach appears warranted.
rate of metastasis to local lymph nodes (iliac, sphincter can be removed without the
sacral, and sublumbar nodes) and distant development of fecal incontinence. PEARLS & CONSIDERATIONS
sites in the body, most frequently the lungs, ○ Recurrence rates are 20%-50% with
liver, spleen, and bone. surgery alone. Comments
• Paraneoplastic hypercalcemia occurs in up ○ Postoperative hypocalcemia can occur in • Many anal sac tumors are diagnosed inci-
to 50% of dogs with anal sac adenocarcinoma previously hypercalcemic patients; careful dentally on physical exam. A rectal exam is

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