Veterinary Society of
Surgical Oncology


General Considerations

  • majority of large intestinal tumors are malignant in dogs


  • mean age 8.5 years (range, 2-14 years)
  • sex predilection: 60%-70% male
  • sites: large intestine and mid-to-distal rectum
  • gross appearance is variable:
  • nodular (single or multiple)
  • pedunculated (mid-to-distal rectum)
  • annular constriction or obstruction (colon to mid-rectum)
  • metastatic rate is highly variable depending on the study

Leiomyoma and Leiomyosarcoma

  • smooth muscle tumors are the most common intestinal mesenchymal tumor
  • mean age 11 years (range, 8-13 years)
  • sites: small intestine and cecum
  • paraneoplastic syndromes include hypoglycemia and high plasma erythropoietin causing secondary erythrocytosis
  • 50% have localized peritonitis as a result of tumor rupture
  • 38%-54% metastatic rate with metastatic sites including the liver, spleen, lungs, kidneys, and diaphragm

Other Large Intestinal Tumors

  • LSA
  • polyp


Clinical Signs

  • tenesmus, hematochezia, dyschezia, and rectal bleeding unassociated with defecation
  • other signs can include vomiting, diarrhea, and weight loss
  • hematochezia uncommon in mesenchymal tumors due to lack of mucosal involvement
  • cecal tumors often present with collapse and septic peritonitis due to perforation


Physical Examination

  • cachexia is common
  • abdominal mass is frequently palpable via either abdomen and rectal palpation
  • other findings include dehydration and abdominal pain

Laboratory Tests

  • anemia and leukocytosis reported but occur less commonly than small intestinal tumors

Abdominal Radiographs

  • abdominal mass is detected in 40%-50% of canine mesenchymal large intestinal tumors
  • abdominal effusion is detected in 20% of cecal leiomyosarcoma secondary to perforation

Contrast Radiography

  • contrast radiographs: mural lesions include luminal filling defect, intestinal wall thickening, mucosal ulceration, abnormal positioning of intestinal loops and constricting annular lesions
  • only 25% of large intestinal leiomyosarcoma required contrast studies for identification


  • endoscopy is recommended prior to definitive treatment
  • biopsy samples should be interpreted histologically as cytologic misdiagnosis is common with intestinal ADC being misdiagnosed as either septic inflammation or LSA
  • biopsy samples are often small and superficial resulting in false-negative diagnosis if lesion is either submucosal or associated with surface ulceration and necrosis

Exploratory Celiotomy

  • definitive diagnosis with exploratory celiotomy and biopsy
  • 50% of large intestinal ADC are associated with annular constrictions
  • leiomyomas and sarcomas are usually large solitary masses growing through the intestinal serosa



  • debilitation and hypoproteinemia may complicate treatment
  • exploratory celiotomy with resection and end-to-end anastomosis with 4-8 cm margins and serosal patching of anastomosis
  • mesenteric and regional lymph nodes should be assessed ± aspirated


  • multiagent protocols recommended for LSA as either adjuvant therapy or sole treatment for diffuse disease
  • chemotherapy is also recommended for cats with intestinal plasmacytoma and MCT
  • no effective chemotherapy for ADC


Leiomyoma and Leiomyosarcoma

  • cecal leiomyoma: 28 month ST (n=1)
  • colorectal leiomyoma: 26 month MST
  • cecal leiomyosarcoma: 7.5-31.0 month MST
  • 54% metastatic rate with spleen and liver common metastatic sites
  • 1-year survival rate 75% and 2-year survival rate 66%
  • furthermore, metastasis at the time of surgery is not a poor prognostic factor with a MST 21.7 months


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