Abstract. Fifty canine gastrointestinal (GI) mesenchymal tumors were examined to determine the occurrence of leiomyomas (LM) and GI stromal tumors and to compare their clinicopathologic features. Twenty-one tumors (42%) were histologically reclassified as gastrointestinal stromal tumors (GISTs) and 29 tumors (58%) as LMs on the basis of their histologic similarity with homologous human tumors. The GISTs occurred equally in males and females, with a mean age of 11 years (range 5-14 years). Five GISTs (24%) were associated with clinical signs and six (29%) had metastasis in liver or abdominal cavity. The GISTs occurred in large intestine (10, 48%), small bowel (six, 29%), stomach (four, 19%), and mesentery of small intestine (one, 5%). Histologically, they were highly cellular spindle, or less commonly epithelioid tumors with mitotic rates ranging from 0 to 19 per 10 HPF. Eleven tumors (52%) were positive for CD117 (KIT); seven (33%) were positive for smooth muscle actin but none for desmin and S-100 protein. Sequences of KIT exon 11, often mutated in human GISTs, were evaluated from four GISTs. Deletion of Try 556 -Lys 557 coexisting with duplication of Gln 555 in one case of GIST and T to C transition resulting in substitution of Pro for Leu 575 in another were identified. The LMs occurred predominantly in males (82%) with a mean age of 11 years (range 8-17 years). Nine tumors (31%) had associated clinical signs. They occurred in the stomach (22, 76%), esophagus (four, 14%), and intestines (three, 10%); all were paucicellular, had no mitoses, and were composed of mature smooth muscle cells. Twenty-eight (97%) were positive for smooth muscle actin and 18(62%) for desmin but none for CD117 and S-100. Both GISTs and true LMs occur in the GI tract of dogs. Both tumors have distinctive pathologic features.

The optimal treatment for squamous and cloacogenic tumors of the anorectum is controversial. Radical surgery, limited surgery, and radiotherapy (XRT) are all potentially curative. This study was undertaken to determine which patients are candidates for each type of treatment and which would benefit from combined treatment. The records of 192 patients treated at this institution between 1954 and 1979 with the diagnosis of squamous or cloacogenic carcinoma of the anorectum were retrospectively reviewed. A subgroup of 132 patients undergoing abdominal perineal resection (APR) was analyzed to determine prognostic factors for these tumors. No survival difference was observed between the two histologic types (P = 0.51). Prognostic variables significant at P = 0.05 or better were sex, size, nodal status, and level of invasion. A new staging system is proposed that utilizes tumor size, invasion, grade, and nodal status. Actuarial 10‐year survival was 100%, 76%, 29%, and 0% for Stages A, B, C and D, respectively (P values 0.22, 0.0007, and 0.01, respectively). Twelve patients undergoing APR received postoperative XRT; when compared by stage with APR alone no survival difference can be shown, although there is a trend towards fewer local recurrences. Of 26 patients (14 Stage B, 12 Stage C) receiving preoperative XRT (average 4000 R) before APR, 10 had inoperable tumors prior to XRT. All became operable. Eight patients had negative surgical margins and survival was equivalent stage for stage to the operable group (Stage B 78%, 5‐year survival; Stage C 43%, 5‐year survival). Eleven patients had no demonstrable primary tumor after XRT, although three had nodal metastasis. Five‐year survival was 83% for this group. Thirty‐one local recurrences were retreated for cure by surgery, XRT, or combination. Actuarial 5‐year survival after retreatment was 38%. Thirty metachronous inguinal metastases were seen, 20 were retreated for cure, 18 by inguinal lymphadenectomy. Actuarial 5‐year survival was 42%. Using a new staging system based on analysis of prognostic parameters for this disease, the outcome of combined surgery and XRT is compared. The efficacy of preoperative XRT for inoperable tumors is demonstrated. An appreciable salvage rate for local or inguinal recurrence was observed. Cancer 53:1285‐1293, 1984.

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A correlation exists between the pathologic stage and the survival rate for adenocarcinoma. The most common recurrence pattern for adenocarcinoma was carcinomatosis, followed in frequency by abdominal wall recurrence. Leiomyosarcoma preferentially metastasizes to the liver.