Anal sac adenocarcinoma

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Pre-operative view of an anal sac adenocarcinoma in a 9-year-old male Akita[1]

Anal sac adenocarcinoma are a relatively rare neoplasia of the anal glands of older dogs, especially German Shepherds and Golden Retrievers.

These tumors are highly metastatic and locally invasive and should be approached cautiously.

Affected dogs usually present with perianal pruritus, anal licking, tenesmus, constipation, scooting, dysuria, hindlimb weakness or acute paralysis (associated with vertebral metastases)[2].

Many clinical symptoms are referable not only to the primary perianal mass but also the cystic metastatic sublumbar lymph nodes which press on vital organs. Secondary anal sacculitis and perineal dermatitis may also be present due to self-trauma.

Manual palpation of the anus in affected dogs may reveal a large mass (sometimes up to 100cm), but some are quite small and cannot be palpated. Regional lymphadenopathy in metastatic cases occurs in many cases, and pulmonary metastasis in about 10% of cases[3].

Diagnosis is based on presenting clinical signs, careful digital examination of the anus, rectum and anal glands, and histological analysis of biopsied material[4]. Fine-needle aspirates of the anal gland are well tolerated in most dogs.

A thorough radiographic study should be performed to exclude metastases in visceral and thoracic organs.

Hematological analysis may reveal hypercalcemia of malignancy (normal range 1.1-1.3 mmol/L). A calcium:phosphate ratio higher than 60 suggests soft-tissue mineralization and impending renal failure, and these cases should be treated aggressively. Disrupted calcium homeostasis is a potential complication following the treatment of long-standing cases[5]. Secondary hypertrophic osteopathy has also been reported[6].

At the time of diagnosis, approximately 50% of dogs have hypercalcemia and 80% have metastases within regional lymph nodes[7].

A differential diagnosis would include mast cell tumor, perianal adenocarcinoma, squamous cell carcinoma, anal gland abscess and perianal fistula.

Treatment usually involves a combination of therapies including surgery, radiation therapy[8] and chemotherapy.

Surgical resection is the mainstay of treatment, including cytoreductive surgery on regional lymph nodes. In dogs with visible metastases within regional lymph nodes, omentalization of regional sublumbar lymph node is recommended for long-term palliation of tenesmus and dysuria[9]. Post-operative infections and fecal incontinence are common complications.

Chemotherapy drugs include melphalan (7 mg/m2 x 5 days every 3 weeks orally indefinitely)[10], actinomycin-D (0.7 - 0.9 mg/m2 every 3 weeks intravenously), doxorubicin (30 mg/m2 every 2 - 3 weeks intravenously), mitoxantrone (5 mg/m2 every 3 weeks for five treatments)[11] or nitrosylcobalamin[12].

Since approximately 20% of anal sac adenocarcinomas express Kit and platelet-derived growth factor receptors[13], toceranib has also been trialed with favourable responses when given at 2.8 mg/kg daily[14].

Corticosteroids such as prednisolone are less effective.

Fecal softeners such as lactulose will help to reduce fecal straining.

The prognosis for most cases is guarded, with survival rates of 1 - 4 years[15], but early detection and aggressive management may result in good quality of life for some years.

References

  1. Veterinary Practice News
  2. Brisson BA et al (2004) Metastatic anal sac adenocarcinoma in a dog presenting for acute paralysis. Can Vet J 45(8):678-681
  3. Chun, R (2009) Anal sac tumors. In Kirk's Current Veterinary Therapy. XIV. Saunders Elsevier, Missouri. pp:382-384
  4. Sakai H et al (2012) Cytologically atypical anal sac adenocarcinoma in a dog. Vet Clin Pathol 41(2):291-294
  5. Saba C et al (2011) Hypocalcemia following surgical treatment of metastatic anal sac adenocarcinoma in a dog. J Am Anim Hosp Assoc 47(6):e173-e177
  6. Hammond TN et al (2009) What is your diagnosis? Metastatic anal sac adenocarcinoma with paraneoplastic hypertrophic osteopathy. J Am Vet Med Assoc 235(3):267-268
  7. Bennett PF et al (2002) Canine anal sac adenocarcinomas: clinical presentation and response to therapy. J Vet Intern Med 16(1):100-104
  8. Keyerleber MA et al (2012) Three-dimensional conformal versus non-graphic radiation treatment planning for apocrine gland adenocarcinoma of the anal sac in 18 dogs (2002-2007). Vet Comp Oncol 10(4):237-245
  9. Hoelzler MG et al (2001) Omentalization of cystic sublumbar lymph node metastases for long-term palliation of tenesmus and dysuria in a dog with anal sac adenocarcinoma. J Am Vet Med Assoc 219(12):1729-1731
  10. Emms SG (2005) Anal sac tumours of the dog and their response to cytoreductive surgery and chemotherapy. Aust Vet J 83(6):340-343
  11. Turek MM et al (2003) Postoperative radiotherapy and mitoxantrone for anal sac adenocarcinoma in the dog: 15 cases (1991-2001). Vet Comp Oncol 1(2):94-104
  12. Bauer JA et al (2010) Anti-tumor effects of nitrosylcobalamin against spontaneous tumors in dogs. Invest New Drugs 28(5):694-702
  13. Brown RJ et al (2012) Expression of PDGFR-β and Kit in canine anal sac apocrine gland adenocarcinoma using tissue immunohistochemistry. Vet Comp Oncol 10(1):74-79
  14. London C et al (2012) Preliminary evidence for biologic activity of toceranib phosphate (Palladia(®)) in solid tumours. Vet Comp Oncol 10(3):194-205
  15. Hobson HP et al (2006) Surgery of metastatic anal sac adenocarcinoma in five dogs. Vet Surg 35(3):267-270
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