+ General Considerations

Majority of large intestinal tumors are malignant in dogs

+ Adenocarcinoma

  • 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

  • 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


+ Surgery

  • 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

+ Chemotherapy

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