If special staining was not performed on the biopsy sample (typically you have to request this), you will want to do so. Many tumors initially classified as leiomyosarcomas are really gastrointestinal stromal tumors (GISTs). In general the STs may not be that different and most cases that are completely excised had longterm survival. The prognosis is better with the GIST tumors. I have one patient now who has been under the care of a oncologist since I surgically removed a cecal GIST 1.5 years ago. She did develop a second tumor in her abdomen near her bladder a few months back, but it was resected completely as well. She is doing great!
I've copied and pasted two papers below that discuss survival times based on the tumor type and location. Please note that it is possible to have obtained a cure if the entire tumor was removed. You may also wish to follow up with a veterinary oncologist to discuss follow-up chemotherapy.
Some papers on reclassification of the tumor type based on special stains and length of survival:
Reclassification of small intestinal and cecal smooth muscle tumors in 72 dogs: clinical, histologic, and immunohistochemical evaluation
Vet Surg. June 2007;36(4):302-13.
Ceriel P H J Maas1, Gert ter Haar, Ingrid van der Gaag, Jolle Kirpensteijn
1 Department of Clinical Sciences of Companion Animals, University of Utrecht, Utrecht, The Netherlands.
OBJECTIVES: To reclassify canine small intestinal and cecal leiomyoma (LM) and leiomyosarcoma (LMS) into smooth muscle and gastrointestinal stromal tumors (GIST) using histologic and immunohistochemical (IH) analysis and to report clinical findings and survival data. STUDY DESIGN: Retrospective review of cases. ANIMALS: Dogs (n=47) with small intestinal (40 LMS; 7 LM) and 25 dogs with cecal tumors (23 LMS; 2 LM). METHODS: Clinical and survival data were reviewed. Tissue sections were reevaluated for light-microscopic malignancy criteria and examined for expression of SMA, desmin, vimentin, S-100, and CD117 (KIT) by immunohistochemistry. RESULTS: Reclassification resulted in 2 LM, 9 LMS, 19 GIST, and 17 GIST-like tumors in the small intestine and 23 GIST and 2 GIST-like tumors in the cecum. GIST-like tumors were morphologic and IH identical to GIST but lacked KIT expression. No significant difference in survival was observed for tumor type, location, histologic, or IH characteristics; however, dogs with cecal tumors were significantly older in age, presented more commonly with intestinal perforation and peritonitis, and less commonly with weight loss. Cecal tumors had more histologic malignancy criteria than small intestinal tumors. After excision, 1 and 2 year recurrence-free periods were 80.1% and 67.2% for small intestinal and 83.3% and 61.9% for cecal tumors. CONCLUSION: Prognosis for intestinal tumors with histologic smooth muscle appearance is good after excision and not related to tumor type, location, histologic, or IH characteristics. CLINICAL RELEVANCE: Clinical importance could not be demonstrated for reclassification, but may be for future treatment, of intestinal smooth muscle or stromal tumors.
Clinical and immunohistochemical differentiation of gastrointestinal stromal tumors from leiomyosarcomas in dogs: 42 cases (1990-2003)
J Am Vet Med Assoc. May 2007;230(9):1329-33.
Kelli N Russell1, Stephen J Mehler, Katherine A Skorupski, Jennifer L Baez, Frances S Shofer, Michael H Goldschmidt
1 Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
OBJECTIVE: To reexamine (via immunohistochemical techniques) canine tissue samples that had been previously classified as gastrointestinal leiomyosarcomas (GILMSs), identify and differentiate gastrointestinal stromal tumors (GISTs) from GILMSs, and compare the biological behavior and clinical course of GISTs and GILMSs in dogs. DESIGN: Retrospective case series. ANIMALS: 42 dogs. PROCEDURES: Medical records of 42 dogs for which a histologic diagnosis of GILMS was confirmed were reviewed for signalment, clinical signs, physical examination findings, results of initial diagnostic tests, surgical findings, adjunctive treatment, location of the tumor, completeness of resection, and outcome after surgery. Archived tumor tissue specimens from each dog were restained via immunohistochemical techniques to differentiate tumor types. Long-term follow-up information was obtained from the medical record or through telephone interviews with owners and referring veterinarians. RESULTS: On the basis of immunohistochemical findings, 28 of 42 tumors were reclassified as GISTs and 4 were reclassified as undifferentiated sarcomas; 10 tumors were GILMSs. In dogs, GISTs developed more frequently in the cecum and large intestine and GILMSs developed more frequently in the stomach and small intestine. Median survival times for dogs with GISTs and GILMSs were 11.6 and 7.8 months, respectively; if only dogs surviving the perioperative period were considered, median survival times were 37.4 and 7.8 months, respectively. These differences, however, were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, many previously diagnosed GILMSs should be reclassified as GISTs on the basis of results of immunohistochemical staining. The biological behavior of these tumors appears to be different.
I hope this information was helpful. I'm pulling for you and your dog. Please let me know how things go, or if you have any other questions.