Anal Sac Adenocarcinoma

Signalment

Have only been confirmed in dogs although they may occur in cats. Predisposed breeds include:

• 

  English Cocker Spaniels

• 

  Springer Spaniels

• 

  Daschunds

• 

  Alaskan Malamutes

• 

  German Shepherds

and mixed-breed dogs

• Mainly older bitches (90%)
• Also in castrated male dogs

Description

A highly malignant neoplasia that readily metastasizes to the medial iliac lymph nodes. Around 50% may lead to paraneoplastic hypercalcaemia due to parathyroid hormone-related peptide. The tumours can be between 1 and 10cm in size and 50% of them will metastasize.

Diagnosis

History and Clinical Signs

See Anal Sac Disease - General

Also:

• Obstipation due to enlarged internal iliac lymph nodes
• Pernieal swelling
• Hypercalcaemia signs including polydipsia, polyuria, anorexia and weight loss.

Rectal examination

Best carried out under general anaesthetic with manual compression of the caudal abdomen towards the rectum.

Biochemistry

To assess:

• Calcium
• Phosphate
• Renal function

Thoracic radiographs

At least two views to check for thoracic metastases.

Abdominal imaging

Caudal lateral abdominal radiographs or abdominal ultrasound to assess the medial iliac lymph nodes for metastases. When enlarged the displace the rectum ventrally as they are found ventral to the lumbar sacral disc.

Needle biopsy

Guided by ultrasound to aspirate the effected lymph nodes.

Treatment

The treatment of choice is surgical excision if the patient is normocalcaemic without any metastases. The success will depend upon the size of the mass.

Adjuvant radiotherapy

Can reduce the local recurrence and used if excision is incomplete. However it may lead to radiation-induced colitis.

Palliative chemotherapy

Using platinum or anthracycline can lead to the primary tumour shrinking before surgical excision.

Treatment of Hypercalcaemia

High fluid rates of 0.9% saline to diurese calcium. Furosemide should be administered (2mg/kg intravenously) once the patient in normocalcaemic.

Prognosis

Potential postoperative complications include infection, wound dehiscence, faecal incontinence and in 25% of cases, local recurrence. Hypercalcaemia reoccurs in 35-50% of cases due to metastases. Serum calcium levels should therefore be reguarly along with evidence of mass regrowth. Post-op survival ranges between 2 and 39 months with the average being 8 months

References

Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA

Merck & Co (2008) The Merck Veterinary Manual

Dobson, J.M. and Lascelles, B.D.X. (2003) BSAVA Manual of Canine and Feline Oncology (2nd Edition) BSAVA