Apocrine adenocarcinomas of the anal sac

Anal sac adenocarcinomas are often suspected due to location and their behaviour, but a biopsy is necessary for a definitive diagnosis. Needle aspiration biopsy is a common first step. Cytopathology reveals clusters of cells with uniform round nuclei. These cells do not have many of the features usually associated with malignancy, such as a high nucleus to cytoplasm ratio or prominent nucleoli. Further cytology of suspected metastases can be performed following ultrasonographic and/or radiographic examination for metastasis (most often locally and to the sublumbar lymph nodes initial stages).

It used to be regarded that all apocrine gland carcinomas carried a very grave prognosis, however, recent journals including the article  in JAVMA (vol 223 no 6 2003 pgs 825-831) performed a retrospective study and found that there was an equal sex predisposition and that the highest survival times were in dogs which were treated with surgery and chemotherapy and also had the smallest clinically palpable tumours. It was also found that 27% of dogs had hypercalcaemia and in those dogs they had a significantly shorter survival time. In most studies however the metastatic rate is considered at least 50%, therefore this tumour generally carries a very poor prognosis.

Paraneoplastic hypercalcaemia (may cause renal damage) and metastasis (to external iliac nodes and less often to liver, spleen and lungs) are common, 25-50% and 50-90% respectively.  Recurrence or persistence of hypercalcaemia following excision of the primary tumour indicates local recurrence and/or metastasis. Early diagnosis and complete excision of a small tumour can be curative but large or nonresectable tumours and the presence of metastasis are poor long-term prognosticators. The average reported postoperative survival time is 8 months, with a range of 2 weeks to 39 months. The reported rate of local recurrence is 25%.

First published: Fri, Oct 29 2010