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.