+ General Considerations

  • Benign and malignant tumors occur with equal frequency in the rectum of dogs
  • Benign tumors include adenomatous polyps which are described as sessile, raised, pedunculated, single, or multiple
  • Malignant rectal tumors in cats and dogs include ADC and LSA
  • Rectal ADC in dogs is described as infiltrative, ulcerative, or proliferative

+ 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

+ Polyps

  • Site: distal rectum
  • 80% are single lesions and 20% are multiple
  • 0%-41% local tumor recurrence rate after surgical resection
  • 18% rectal polyps undergo malignant transformation
  • Tenesmus, hematochezia, dyschezia, rectal bleeding unassociated with defecation, and polyp prolapse
  • Other signs can include vomiting, diarrhea and weight loss


+ 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
  • Paraneoplastic leukocytosis reported with adenomatous rectal polyp

+ 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



+ Surgical Techniques

  • Surgical approaches: rectal eversion, rectal pull-through, or resection and end-to-end anastomosis
  • Fecal incontinence is uncommon if rectal resection < 4 cm
  • However, fecal incontinence and incisional dehiscence is common if > 4 cm rectum is resected with rectal pull-through surgery
  • Transanal endoscopic resection of benign rectal tumors has been described in 6 dogs
  • Incontinent end-on colostomy has been described in the management of 1 dog with rectal ADC

+ Cryosurgery

  • Cryosurgery has been used in 1 dog rectal leiomyosarcoma complications include rectal prolapse, perineal hernia, and stricture formation
  • Cryosurgery of pedunculated stalk can be considered with rectal polyps

+ Chemotherapy

  • 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, but combination of 5-fluorouracil and cisplatin may be effective
  • Piroxicam (suppository or oral) for rectal tubulopapillary polyps with significant PR or CR in 88% (7/8)


+ Rectal Polyp

  • 0%-41% local tumor recurrence rate after surgical resection or cryosurgery
  • 18% rectal polyps undergo malignant transformation
  • Survival time > 1 year with few deaths related to polyp
  • Survival time for polyps diagnosed as carcinoma in situ 5-24 months

+ Benign Rectal Tumors

  • 5 dogs alive between 5-20 months after surgery
  • 3 local recurrence with recurrence as carcinoma in one dog

+ Rectal Carcinoma

  • Mean survival time 22 months following surgery
  • Radical surgery associated with high complication rate and poor survival (< 1 week)
  • Local appearance may be predictive of survival:
  • Mean survival time 32 months if pedunculated
  • Mean survival time 12 months if nodular or cobblestone
  • Mean survival time 1.6 months if annular
  • Mean survival time 24 months following cryosurgery
  • Survival times following electrocautery are reported between 18-29 months
  • MST 7 months following intraoperative orthovoltage radiation therapy with 12-month survival rate 67%, local tumor recurrence in 54%, and median DFI 6 months