Introduction

• Anal sac disease is common in the dog (affecting ~12% of the population) but neoplasia is an uncommon clinical finding.
• When neoplasia does occur, the majority of anal gland tumors are perianal adenomas Perianal neoplasia of intact male dogs.
• The most common malignancy of the perineal region is adenocarcinoma of the apocrine glands (within the anal sac).
• The tumor represents approximately 2% of canine skin neoplasms.
  Print off the owner factsheet Anal sac gland carcinoma to give to your client.

Pathogenesis

Etiology

• Malignant transformation of the apocrine components/glands located within the connective tissue stroma and near the fundic portion of the anal sac.

Predisposing factors

General

• Breed, age (7-12 years) and possibly sex (female, neutered male).

Pathophysiology

• Geotopical distribution of masses originate within the apocrine glands within the lining of the anal sac. There is a propensity of these tumors to metastasize to the regional (iliac/sub-lumbar) lymph nodes early. Later metastatic lesions appear within the liver, spleen, lungs and other sites.
• In some animals, the space occupying effect of the mass is identified by the pet owner prompting consultation with a veterinarian. If a perianal swelling is not identified then a pet may simply present based on the effects of metastatic disease (stool shape change, paraparesis, tenesmus or constipation) or from paraneoplastic hypercalcemia (pseudo hyperparathyroidism-associated polyuria and polydipsia).
• This is a highly invasive and metastatic tumor. In fact, the primary tumor burden in the pet may be incidental and barely palpable before metastatic disease is present. Because metastasis is generally, and initially, to the regional nodes, multimodality treatments (surgery with chemotherapy and/or radiation treatment) are generally favorable for median survivals beyond one year.
• The neoplasm causes hypercalcemia by secretion of a parathyroid hormone-related protein (PTHrP PTHrP assay ) - humoral hypercalcemia of malignancy. This protein is seen in various normal tissues, presumably as a paracrine factor.
• PTHrP stimulates osteoclastic bone resorption, increased renal tubular calcium reabsorption, and decreased renal tubular phosphate reabsorption.
• Tumor removal typically allows calcium to return to normal (until metastatic disease recurs).

Diagnosis

Treatment

Prevention

Outcomes