Page 1353 - Clinical Small Animal Internal Medicine

142 Cancer of the Small and Large Intestine 1291

can be attempted. A study evaluating lomustine for cats Many animals with intestinal neoplasia need support-
VetBooks.ir with a variety of mast cell tumors (cutaneous, splenic, ive medications for nausea, decreased appetite, gastroin-
testinal protection, and diarrhea. The most commonly
intestinal) found that two cats with intestinal mast cell
tumors responded. Whether lomustine would be effec-
dolasetron, and metoclopramide. Appetite stimulants
tive in a large population of cats with intestinal mast cell used antiemetics include maropitant, ondansentron,
tumors is unknown. Other chemotherapy agents used in include capromorelin, mirtazapine, cyproheptadine, and
dogs with mast cell tumors include vinblastine, cyclo- megestrol acetate. Effective gastroprotectants include
phosphamide, hydroxyurea, and prednisone. Their effec- famotidine, omeprazole, and sucralfate. Common antidi-
tiveness in cats with mast cell tumors is unknown. arrheal medications include metronidazole, tylosin, sul-
Many cat mast cell tumors have mutations in the gene fasalazine, and loperamide.
c‐kit leading to constitutive activation of the tyrosine
kinase growth factor receptor KIT. Activating mutations
of c‐kit have been implicated in mast cell tumor develop- Prognosis
ment and progression in dogs. Small molecule targeted
therapies (toceranib phosphate and masitinib meslyate) The prognosis for dogs with intestinal lymphoma is
have been approved for use in dogs with mast cell tumors. generally much worse than for dogs with multicentric
As mentioned previously only toceranib phosphate is lymphoma. A recent study using a CHOP‐based proto-
approved for use in the USA. These targeted therapies col with consolidation resulted in a 56% response rate
inhibit the activation of the abnormal growth factor (50% complete response, 6% partial response). The
receptor KIT, resulting in cessation of cell growth and median survival time for the entire study population
proliferation and potentially leading to cell death through was 2.5 months. The response rate for dogs with multi-
apoptosis. A recent study evaluating Palladia in cats with centric lymphoma is up to 90–95% with median sur-
mast cell tumors reported a clinical benefit in 76% vival times of 12–18 months. Another study evaluating
(13/17) of those with the gastrointestinal form. However, dogs with intestinal lymphoma treated with multiple
further studies are necessary. treatment modalities revealed very poor survival, with a
Aside from definitive treatment with chemotherapy median survival time of 13 days. In dogs with intestinal
and/or a tyrosine kinase inhibitor, all patients with intes- lymphoma, the presence of diarrhea and lack of
tinal mast cell tumors should receive prednisolone or response to chemotherapy were negative prognostic
prednisone as well as a histamine receptor 1 and 2 factors
antagonist. In dogs treated with surgical excision for small intesti-
For dogs with colorectal polyps, the use of NSAIDs has nal adenocarcinoma, the presence of metastasis at the
been found to be of benefit in reducing clinical signs and time of surgery is associated with statistically shorter
may be an alternative treatment to surgical excision. The survival time (median survival time three months, 20%
author recommends placing dogs that have had surgical survival at one year) when compared to dogs without
removal of colorectal polyps on NSAIDs postoperatively metastasis (median survival time 15 months, 66.7%
in an attempt to prevent local recurrence, development survival at one year).
of additional polyps or malignant transformation of pol- Long‐term survival has been reported in dogs with
yps. Although there are no clinical studies evaluating the metastatic intestinal leiomyosarcoma. In one study, 50%
use of NSAIDs in this particular setting, NSAIDs have of dogs with intestinal leiomyosarcomas had metastasis
been found to have various antineoplastic properties. at the time of surgery. The median survival time of the
Surgical excision of colorectal plasmacytomas is cura- entire study population was 21.3 months. Another study
tive in most cases. Plasmacytomas of other areas of the revealed a median survival time of 1.1 years for dogs
intestinal tract can have a high metastatic rate and if with small intestinal leiomyosarcoma that survived the
metastasis is observed, follow‐up chemotherapy in the immediate postoperative period, with 29% of the dogs
form of prednisone and melphalan is recommended. dying of leiomyosarcoma. The results of these historical
Extraskeletal osteosarcomas are both locally and system- studies should be viewed in light that some might have
ically aggressive. Adjuvant chemotherapy has been been GISTs that had been misdiagnosed. In one study
shown to help prolong survival in dogs with extraskeletal evaluating both GISTs and leiomyosarcomas, the median
osteosarcoma. Therefore, postoperative carboplatin is survival time for dogs with GISTs that survived the peri-
recommended for intestinal extraskeletal osteosarcoma. operative period was 37.4 months, whereas the median
Visceral hemangiosarcoma is an aggressive disease with survival time for dogs with leiomyosarcomas was only
a high rate of metastasis. Adjuvant doxorubicin chemo- 7.8 months. Further, 7% of the dogs with GISTs devel-
therapy is recommended after surgical resection of intes- oped metastasis. There were no reports of metastasis in
tinal hemangiosarcoma. those with leiomyosarcomas.