Page 1350 - Clinical Small Animal Internal Medicine

1288 Section 11 Oncologic Disease

The intestinal lesion with feline intestinal mast cell pacemaker cells of the intestinal tract and regulate peri-
VetBooks.ir tumor can be diffuse, solitary or multifocal. The neopla- stalsis. Tumors derived from these cells are called gas-
trointestinal stromal tumors (GISTs). GISTs can be
sia may be either intraluminal or intramural. The small
intestine is the most common location for feline intesti-
expression of c‐kit (CD117). In one recent study, two‐
nal mast cell tumor but colonic involvement can occur. distinguished from leiomyosarcomas based on the
Widespread metastasis is common at the time of diagno- thirds of dogs diagnosed with intestinal leiomyosarco-
sis. One study found that 64% of cats with intestinal mast mas were reclassified as GISTs based on positive staining
cell tumor had multiorgan involvement. The most com- for CD117. In this study, GISTs were most common in
mon sites of metastasis include lymph nodes, liver, the cecum and large intestine (64%) as compared to the
spleen, and rarely lung. Intestinal mast cell tumors can be stomach and small intestine (36%). In oposition to
difficult to diagnose because their cytoplasmic granules GISTs,leiomyosarcomas appear to develop more com-
may not stain. This may be due to their anaplastic nature monly in the stomach and small intestine (90%) and are
or degranulation. It has been suggested that mucosal less common in the large intestine (10%).
mast cells are different from mesenchymal mast cells and It is reported that up to 60% of all intestinal tumors in
require special fixation to enhance the metachromasia. dogs are located in the colon and rectum. Dogs are typi-
Diff‐Quik staining of feline mast cell tumors sometimes cally middle‐aged to older with males reported to be
fails to reveal cytoplasmic granules. Circulating mast affected more frequently than females. Unlike in the
cells are uncommon with intestinal mast cell tumors, small intestine, adenomatous polyps and carcinoma in
although peripheral eosinophilia has been reported. situ are commonly identified in the large intestine.
Adenomatous polyps and carcinoma in situ are usually Malignant tumors, such as those that develop in the
solitary. However, multiple and diffuse varieties have small intestine also occur.
been identified. Furthermore, malignant transformation Lymphoma is the most common intestinal neoplasia in
to invasive carcinoma has been reported. cats. It is the most common anatomic form of lymphoma
Canine colorectal adenocarcinoma generally can be in cats since the advent of FeLV vaccine as well as routine
grouped into three categories based on its gross appear- FeLV testing and separation of FeLV‐positive cats.
ance: pedunculated, cobblestone, and annular. When Anatomic forms of feline lymphoma generally associated
metastasis does occur with colorectal adenocarcinoma, with FeLV infection, such as the mediastinal and nodal
it usually travels via lymphatics to the local lymph nodes forms, are becoming less prevalent. Adenocarcinoma is
and may sometimes seed the peritoneum, leading to car- the second most common small intestinal tumor in cats.
cinomatosis. The metastatic rate for colorectal adenocar- Siamese may be overrepresented. Intestinal mast cell
cinoma ranges from 0% to 80%. Malignant transformation tumor is the third most common intestinal tumor in cats.
from in situ tumors has been reported in 17–50% of dogs. Colonic adenocarcinoma (along with lymphoma) is one
Approximately 75% of cats with colonic adenocarci- of the two most common neoplasias that develop in the
noma have metastasis. Half have distant metastasis and feline large intestine.
half are local. Metastatic sites included the colonic lymph Other less common intestinal tumors include
nodes, mesenteric lymph nodes, liver, omentum, and extramedullary plasmacytoma, extraskeletal osteosar-
lungs. Carcinomatosis may also occur. coma, and hemangiosarcoma.

Epidemiology Signalment

Small intestinal tumors are in general, uncommon in The median age for dogs with all types of lymphoma,
dogs. According to most reports, lymphoma is the most including intestinal, is 6–9 years. Small intestinal neo-
common specific type. The intestinal tract is the most plasia should be considered a differential diagnosis in a
common extranodal site for this malignancy, affecting middle‐aged to older dog with signs consistent with
5–7% of all dogs diagnosed. Intestinal adenocarcinoma intestinal obstruction. The median age of onset for
and leiomyosarcoma are the two most common nonlym- canine intestinal leiomyosarcoma/GIST is 10.5 years.
phomatous small intestinal tumors in dogs. In particular, They are reportedly more common in female dogs. Dogs
leiomyosarcoma is the most frequently diagnosed intes- with colorectal polyps have a mean age of 7–8 years.
tinal sarcoma and it commonly involves the jejunum and Colorectal adenocarcinoma most commonly affects
cecum. older male dogs. Feline intestinal lymphoma is more
Recently, it was found that tumors previously catego- common in older cats with a median of age of 10–12
rized as leiomyosarcomas were in fact derived from the years. Domestic short‐hairs are more commonly
interstitial cells of Cajal. Interstitial cells of Cajal are the affected. The average age of cats with small intestinal