GENERAL CONSIDERATIONS
Biologic Behaviour
General Considerations
- intestinal tumors are uncommon and account for 3% of canine tumors
- intestinal tumors (small and large) account for 92% of all non-oral GI tumors
- large intestinal tumors are more common than tumors of the small intestine
- 80% of dogs > 7 years
- 88% malignant and 12% benign (i.e., leiomyoma and polyp)
- sex predilection: 60%-70% male for non-lymphoid intestinal neoplasia
- breed predisposition: GSD and Collie
Lymphosarcoma
- intestinal LSA is the most common intestinal tumor
- majority are multifocal and involve the small intestine
Adenocarcinoma
- age: mean 9 years (range, 1-14 years)
- sites: large intestine and mid-to-distal rectum
- pseudomyxoma peritonei has been reported in 1 dog with small intestinal ADC and is characterized by deposition of mucinous pools on serosal surfaces and gelatinous ascites
- 44% metastatic rate for small intestinal ADC with metastatic sites including the regional lymph nodes, mesentery, and liver ± spinal meninges and testes
Leiomyoma and Leiomyosarcoma
- smooth muscle tumors are the most common intestinal mesenchymal tumor
- mean age 9 years (range, 4-14 years)
- sites: small intestine and cecum
- 50% have localized peritonitis as a result of tumor rupture
- intestinal leiomyosarcoma has been reported as a cause of nephrogenic diabetes insipidus in 1 dog
- 38%-54% metastatic rate with metastatic sites including the liver, spleen, lungs, kidneys, and diaphragm
Mast Cell Tumor
- signalment: purebred male dogs of miniature breeds
- clinical signs: anorexia, lethargy, vomiting, and diarrhea
- hematology: anemia, hypoproteinemia, and mastocytemia are common
- GI ulceration is a common finding
- 100% metastatic rate with metastatic sites including regional lymph nodes (common), liver, spleen, heart, and lungs
Other
- intestinal carcinoids are rare
- Goblet cell carcinoid (characterized by features consistent with both carcinoid and ADC) has been reported
- secretory (IgG) and non-secretory extramedullary plasmacytoma
- FSA
CLINICAL FEATURES
Clinical Signs
- anorexia, weight loss, intermittent vomiting, and diarrhea
- severe, persistent vomiting is occasionally observed if proximal small intestinal tumor causes obstruction
Diagnosis
Physical Examination
- palpable abdominal mass and cachexia are common
- other findings include dehydration and abdominal pain
Laboratory Tests
- anemia and leukocytosis are common in dogs with non-lymphoid intestinal tumors
- anemia and hypoglycemia are common in dogs with intestinal leiomyosarcoma
- mesenchymal tumors are associated with microcytic hypochromic anemia, hypoproteinemia, and mild leukocytosis
Abdominal Radiographs
- abdominal mass, obstruction, or persistent irregularity of bowel appearance are identified in 25% of small intestinal tumors and nearly 50% of non-lymphoid intestinal tumors
- abdominal mass is detected in 60% of canine mesenchymal small intestinal tumors
Contrast Radiography
- intestinal mass identified in 57% of dogs with non-lymphoid intestinal tumors
- contrast radiographs: mural lesions include luminal filling defect, intestinal wall thickening, mucosal ulceration, abnormal positioning of intestinal loops, and constricting annular lesions
Ultrasonography
- intestinal mass identified in 87% (13/15) dogs with non-lymphoid small intestinal tumors
- intestinal ADC are transmural, poorly echogenic, and associated with complete loss of wall layering, increased intestinal wall thickness (median 12 mm), luminal fluid accumulation proximal to the lesion (81%), and regional lymphadenopathy (57%)
- loss of wall layering is an excellent predictive factor for differentiating intestinal neoplasia from enteritis in dogs (99% v 12%) with intestinal tumors 50.9-times more likely to have loss of wall layering
- intestinal tumors also have significant increases intestinal wall thickness (15 mm v 6 mm) and are significantly less likely to have diffuse intestinal involvement (2% v 72%)
Exploratory Celiotomy
- definitive diagnosis with exploratory celiotomy and biopsy
- majority of small intestinal ADC are associated with annular constrictions
- leiomyomas and sarcomas are usually large solitary masses growing through serosa
TREATMENT
Surgery
- debilitation and hypoproteinemia may complicate treatment
- exploratory celiotomy with resection and end-to-end anastomosis with 4-8 cm margins and serosal patching
- mesenteric and regional lymph nodes should be assessed ± aspirated
Chemotherapy
- multiagent protocols recommended for LSA as either adjuvant therapy or sole treatment for diffuse disease
- chemotherapy is also recommended for plasmacytoma and MCT
- no proven chemotherapy for ADC, but combination of 5-fluorouracil and cisplatin may be effective
- second-look surgery recommended for evaluation of response to chemotherapy
PROGNOSIS
Adenocarcinoma
- MST 272-300 days
- sex is a prognostic factor with MST for male dogs 272 days v 28 days for female dogs
Leiomyosarcoma
- MST 13.0-21.3 months after surgical resection
- 1-year survival rate 75% and 2-year survival rate 66%
- 54% metastatic rate, but metastasis is not a poor prognostic factor with a MST 21.7 months
Mast Cell Tumor
- MST 16 days with 100% tumor-related mortality within 2 months of diagnosis
- 100% metastatic rate
SMALL INTESTINAL TUMORS