Veterinary Society of
Surgical Oncology

BIOLOGIC BEHAVIOUR

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

DIAGNOSIS

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

TREATMENT

Surgery

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)

PROGNOSIS

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

RECTAL TUMORS

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