COLORECTAL tumors

BACKGROUND

Large intestinal tumors are rare in cats and dogs. The majority of intestinal tumors are malignant and include lymphoma (especially cats), adenocarcinoma and leiomyosarcoma. Benign large intestinal tumors include leiomyoma and rectal polyps. The metastatic risk for malignant tumors is moderate with metastasis to the regional lymph nodes, liver and lungs relatively common.

DIAGNOSIS

Ultrasonography is recommended for both diagnosis and clinical staging. Other diagnostic tests include contrast radiographs (barium study) and colonoscopy. A preoperative diagnosis is sometimes not possible and surgery may be required to both diagnose and treat gastric tumors.

CLINICAL STAGING

An abdominal ultrasound is recommended to check for metastasis to the regional lymph nodes and liver. Chest radiographs or CT scans are done to check for metastasis to the lungs.

TREATMENT

The majority of intestinal tumors are treated with surgical resection with wide margins (3-5 cm) and end-to-end anastomosis. The surgical approach depends on the location of the tumor. Some tumors can be excised from an abdominal approach (which may need to be combined with a pubic symphyseal separation or bone flap for adequate exposure) while others can be approached from the perineum (ie, rectal pull-through procedure).

Rectal polyps are simply treated with rectal eversion and submucosal excision. Non-steroidal anti-inflammatory drugs are recommended after surgical excision of rectal polyps to minimize the risk of local recurrence or malignant transformation.

Lymphoma can be treated with multiagent chemotherapy protocols, but surgery is often required for definitive diagnosis.

PROGNOSIS

The median survival time for cats with intestinal lymphoma treated with chemotherapy is 201-280 days. The prognosis is better for cats responding to chemotherapy with a median survival time greater than 11 months. The median survival time for cats with surgically excised intestinal adenocarcinoma is up to 15 months and this is not decreased by metastasis to the lymph nodes. The prognosis is very poor for cats with intestinal mast cell tumor because of widespread metastasis at the time of diagnosis. 

In dogs, the mean survival time following surgical resection of rectal carcinomas depends on the gross appearance of the tumor and ranges from 1.6 months for annular carcinomas to 12 months for nodular carcinomas and 32 months for pedunculated carcinomas. The prognosis is excellent following excision of rectal polyps as most dogs are cured.

To be updated