Adenocarcinoma

Adenocarcinoma- histological (Courtesy of BioMed Image Archive)

Introduction

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 Adenocarcinoma

Intestinal adenocarcinomas are a reasonably common malignant neoplasm of dogs and cats arising from the epithelial lining of the gastrointesinal tract. As yet, no causative organism or chemical agent has been identified for intestinal adenocarcinomas, but experiments have suggested that nitrosamines may have a role. Intestinal adenocarcinomas can be nodular or annular in appearance. By the time of diagnosis, they have often metastasised via the lymphatic and vascular routes, most commonly to the mesenteric lymph nodes. Other sites of metastasis include the liver, kidneys, peritoneal cavity, omentum and lungs. Intestinal adenocarcinomas display aggressive local growth and invasion, and tumours frequently recur after resection.

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.

Anal Sac Adenocarcinoma

Anal sac adenocarcinoma is 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