14 year old Cairn Terrier

Signalment: 14-year-old M/N Cairn Terrier

History/Physical exam: Thickening of left anal gland

Click here for the IDEXX Pathology Report on this case.

Microscopic description: Cellularity is high consisting of epithelial cells that are present in moderately cohesive clusters or in acinar arrangements. The cells are approximately 15 um in diameter with variably-distinct cell margins. Many free nuclei are present. Some of the cell nuclei appear to float on a raft of grainy basophilic cytoplasm. Nuclei are round to oval with somewhat smudged chromatin and 0-2 variably-distinct, small nucleoli. Anisokaryosis is mild to moderate.

Microscopic interpretation: Apocrine gland adenocarcinoma of the anal sac

Discussion: This is a common tumor in dogs (age range 5-15 years) and relatively uncommon tumor in cats (age range 6-17 years). Approximately 50% of the neoplasms will present as exophytic masses that are easily visualized and 50% will only be found on physical examination or rectal palpation. Apocrine gland adenocarcinoma of anal sac will often spread along the rectum in the pelvic canal. Rate of growth is variable but often slow; however, metastasis occurs in majority of cases including regional lymph nodes (sacral, iliac, sublumbar), lungs, spleen, and liver. This malignancy is often associated with a paraneoplastic syndrome of hypercalcemia (in dogs).


  1. M., A., & M., D. (2009). Anal Sac Gland Carcinoma in 64 Cats in the United Kingdom (1995-2007). Veterinary Pathology, 46(4), 677–683. https://doi.org/10.1354/vp.08-VP-0257-S-FL
  2. Goldschmidt, M.H. & Goldschmidt, K.H. (2016) Epithelial and Melanocytic Tumors of the Skin. In D. J. Meutin (Ed.), Tumors in Domestic Animals 5th edition (pp. 120-122).

Leave a Reply