Adenocarcinoma

Adenocarcinoma- histological (Courtesy of BioMed Image Archive)

• Adenocarcinoma is the most common gastric neoplasm in small animals.
  • This is a tumour of the mucosal epithelium.
• These are genreally found in the fundus (particularly along the lesser curvature), and in the pylorus.
• There are two main internal appearances of gastric adenocarcinoma, both of which show thickened, oedematous, pale and firm tissue:
  

  Adenocarcinoma- gross (Courtesy of BioMed Image Archive)
  1. A diffuse infiltration of gastric mucosa by neoplastic glandular epithelial cells.
     • Causes a diffuse rugal thickening.
  2. A more solitary lesion that is seen as a thick plaque-like lesion
     • Generally has a central erosion/ulceration of the tumour tissue.
       • Distinguishable from a peptic ulcer as the edges of the eroded area are raised and thickened (tumour tissue).
• The external appearance of an affected stomach can include thickening of the draining lymphoid vessels due to tumour infiltration ('cording of the lymphatics') and evidence of a scirrhous reaction to the carcinoma.
• Adenocarcinomas are locally aggressive and spread via the lymphatics to the lymph nodes, lung, liver and adrenal glands.

Intestinal

• An intestinal adenocarcinoma is a malignancy of epithelial cells from the intestinal mucosa.
• Found in both the small and large intestines
  • Common in the canine rectum.
• Species affected:
  • Fairly common in dog and cat.
  • Seen related to bracken ingestion in the older sheep.
  • Occasionally occur in horses.
• These tumours usually grow away from the mucosa, down through the muscularis mucosae and into the submucosa, muscular layers and the serosa.
  • They may, however, project into the lumen.
• Intestinal adeocarcinomas may take an annular form.
  • This may result in stenosis of lumen
    • Muscle proximal to the lesion becomes hypertrophied and dilated.
• Spread may be
  1. Via the lympahtics.
     • To the lymph nodes, lung and liver.
  2. Transcoelomic spread
     • Small, white plaques on serosa and adjacent tissues e.g. diaphragm.

Tumours of the Perianal Area

Adenocarcinomas of the Glands of the Anal Sac (Apocrine Glands)

• Apocrine glands are the true anal glands- not to be confused with the anal sacs or the perianal glands.
• Much less common than intestinal adenocarcinoma.
• Commoner in bitches than dogs.
• Can be bilateral.
• Consequences:
  • May cause local problems.
  • May metastasise.
  • Often secrete a parahormone-like substance to cause paraneoplastic syndrome.
    • This can arise even when the primary tumour is very small.
    • Results in bone resorption and hypercalcaemia,
      • In turn can cause renal failure. which in turn can cause renal failure.