Anal Sac Adenocarcinoma
 |
This article has been peer reviewed but is awaiting expert review. If you would like to help with this, please see more information about expert reviewing. |
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 (PTH-rP). The tumours can be between 1 and 10cm in size and 50% of them will metastasize.
Signalment
Have only been confirmed in dogs although they may occur in cats. Typically older bitches (greater than 10 years) are affected (90% of cases) however male dogs are occasionally affected. Predisposed dog breeds include the German shepherd dog, cocker spaniel, welsh spaniel and standard dachshund.
Diagnosis
History and Clinical Signs
See Anal Sac Disease - General
Also: Obstipation due to enlarged internal iliac lymph nodes and Perineal swelling. Additionally signs of hypercalcaemia including polydipsia, polyuria, anorexia and weight loss.
Rectal examination
Tumours of the anal sac can be detected by digital rectal palpation of the anal sac and associated structures, this must be performed with care as frequently the tumours are small and unilateral. Best carried out under general anaesthetic with manual compression of the caudal abdomen towards the rectum.
Laboratory Tests
Serum Biochemistry: Hypercalcaemia is present in 50%-90% of dogs with anal sac adenocarcinoma. This is thought to occur due to the expression of a gene for parathyroid hormone-related peptide by the tumour. Parathyroid hormone-related peptide has actions similar to parathyroid hormone, it acts to increase calcium levels in the blood. In severe cases of hypercalcaemia organ function can become compromised changing specific parameters on the biochemistry panel.
Urinalysis: Patients may be dehydrated with a pre-renal azotaemia due but have a relatively low urine specific gravity.
Radiography
Thoracic Radiography
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 they displace the rectum ventrally.
Sites of metastasis include the liver, spleen, abdominal lymph nodes and the lungs.
Biopsy
Ultrasound guided needle biopsy and histopathology of 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. Radiotherapy, however 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 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 regularly checked along with evidence of mass regrowth. Post-op survival ranges between 2 and 39 months with the average being 8 months.
Literature Search
Use these links to find recent scientific publications via CAB Abstracts (log in required unless accessing from a subscribing organisation).
Anal Sac Adenocarcinoma publications
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