Page 489 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 23 Cancer of the Gastrointestinal Tract 467

the mass. 537 For malignant rectal tumors, full-thickness removal MCT with metastasis to the spleen. A strong PR was seen but was
of the rectum is generally indicated. Rectal-pull through is com- brief in duration. 547
A reduction in the size and clinical signs of rectal polyps in 8
monly performed for rectal adenocarcinomas. This can be per-
VetBooks.ir formed through either a perineal or combined perineal-abdominal dogs was noted after piroxicam therapy, either orally or in sup-
Complications are relatively common, including
538,539
approach.
pository form. Clinical response did not relate to whether there
fecal incontinence (57% total with 40% permanent fecal incon- was inflammation associated with the tumor. 502
tinence), diarrhea (43%), tenesmus (31%), stricture formation
(21%), rectal bleeding (11%), dehiscence (8%), and infection Radiation Therapy
(5%). 538 Colostomy use has been reported to aid in management
of dogs with nonresectable rectal tumors. In one report, skin exco- RT is seldom used in the treatment of intestinal tumors because of
riation was the most common complication, but colostomy bags the concern regarding toxicity to surrounding abdominal viscera,
were managed for up to 7 months. 540 the ability to often obtain adequate local control via surgery, and
For rectal polyps and carcinomas in situ, depending on the sur- the inability to reliably irradiate the same tissue each day because
gical technique used for resection, local recurrence of clinical signs of the mobility of the intestine.
is reported in up to 41% of dogs and 18% of dogs had malig-
nant transformation associated with tumor recurrence. 455 Surgical Prognostic Factors
removal of duodenal polyps in cats is typically curative. 446 For
dogs with colorectal adenocarcinoma, local excision results in Intestinal perforation does not appear to be a negative prognos-
MSTs of 2 to more than 4 years compared with 15 months for tic factor for leiomyosarcoma because dogs surviving the periop-
stool softeners alone; 474,475,539,541 colorectal EMPs and polyps also erative period had prolonged STs in one series. 451 For colorectal
fare well with MSTs of 15 months and 2 years or more, respec- tumors, treatment is prognostic, with local excision resulting in
tively, after surgical excision. 464,542 significantly better outcomes than palliative care. Gross appear-
In cats with large intestinal neoplasia, STs after surgery alone ance, although not statistically examined, may determine outcome
are approximately 3.5 months for lymphoma, 4.5 months for ade- because dogs with annular, obstructing masses survived a mean
nocarcinoma, and 6.5 months for MCT. Subtotal colectomy has ST of 1.6 months whereas dogs nodular/cobblestone masses or
been recommended for cats with colonic adenocarcinoma. 447,543 single pedunculated masses had mean STs of 12 and 32 months,
Adjuvant chemotherapy has improved STs for cats with adenocar- respectively. 474
cinoma, but not for lymphoma. 447 For nonlymphomatous small intestinal tumors in dogs, metas-
tasis at the time of surgery resulted in significantly shorter STs (3
Chemotherapy months vs. 15 months). The 1-year survival rates for dogs with
and without LN metastasis were 20% and 67%, respectively. 441 In
No randomized studies exist to investigate the efficacy of adjuvant another study, however, dogs with and without visceral metastasis
chemotherapy after resection of epithelial intestinal tumors in dogs from leiomyosarcoma survived equally as long after surgical resec-
and cats. The benefit of adjuvant chemotherapy in humans is ques- tion (21 months). 451 Male dogs with small intestinal adenocarci-
tionable, although current fluorouracil-based regimens are often noma had a significantly better outcome; however, the number of
considered to be the standard of care. When attempted, adjuvant female dogs in that study was low. 456 Cats with adenocarcinoma,
chemotherapy typically includes doxorubicin in veterinary medi- however, survived significantly longer if they were treated with
cine. One retrospective study in cats with colonic adenocarcinoma subtotal colectomy (138 days vs. 68 days with mass excision),
treated with subtotal colectomy did show a significant survival received postoperative doxorubicin (280 days with vs. 56 days
advantage for cats receiving adjuvant doxorubicin; MSTs were without doxorubicin), and had no LN metastasis at surgery (259
280 days with and 56 days without chemotherapy. 447 In another days for no LN metastasis vs. 49 days with LN metastasis). 447 For
retrospective study using adjuvant carboplatin, the MST was 269 further details about prognosis for dogs and cats with intestinal
days, but no controls were included to evaluate treatment without MCT see Chapter 21. For prognostic factors for canine and feline
chemotherapy. 543 Distant and nodal metastases were found to be alimentary lymphoma see Chapter 33, Sections A and B.
negative prognostic indicators, with an MST of 200 days versus
340 days and 178 days versus 328 days, respectively. 543 For carci- Comparative Aspects
nomatosis, intracavitary therapy may be helpful with carboplatin
for cats or cisplatin or 5-fluorouracil (5-FU) for dogs. 544 For fur- Although cancer of the large intestine and rectum is well char-
ther details about treatment of alimentary lymphoma please see acterized in humans, small intestinal neoplasia is rare. Theories
Chapter 33, Sections A and B. for this discrepancy include more rapid small intestinal transit
Individual case reports in dogs using receptor tyrosine kinase time compared with the large intestine (creating less contact time
inhibitors (TKIs, imatinib and toceranib phosphate) to treat for carcinogens), dilution of carcinogens with fluid compared
GISTs in the setting of metastatic disease, nonresectable disease, or with solid stool, differences in pH, relative lack of bacteria to
recurrent disease have shown good responses with partial (PR, n = allow transformation of procarcinogens, presence of detoxifying
1) or complete responses (n = 2) for greater than 140 days, greater enzymes, and increased presence of immunoglobulin A promoting
than 9 months, and greater than 4 years, respectively. 486,545,546 local immunosurveillance of damaged cells as a result of increased
The only toxicity seen was in one dog, and this manifested as an lymphocytes in the small intestine. This is in contrast to veterinary
increase in ALT resulting in dose reduction of imatinib. 546 After medicine where in cats and sometimes dogs, malignant neoplasia
this dose decrease, the PR ceased, which could have been due to is more common in the small intestine than the large intestine.
the lower dose or emergence of resistance as has been documented This may reflect differences in physiology, diet, or genetics. As
in human GISTs due to a second site mutation in c-kit. 546 Ima- in animals, tumors of the small intestine of humans are usually
tinib has also been reported in the treatment of canine intestinal malignant. Diagnostic evaluation is similar to that described in