+ Biologic Behavior

  • 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 lung

+ 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 Signs

+ 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


+ 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


+ 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