General Considerations

•intestinal MCT is the 3rd most common feline GI tumor (after LSA and ADC)

•mean age 13 years

•histology: poorly differentiated MCT with less prominent cytoplasmic granules

•more commonly involves small intestine with equal distribution between duodenum, jejunum, and ileum

•< 15% have colonic involvement

•peritoneal effusion relatively common, but peripheral mastocytosis and eosinophilia rare

•metastasis is common and sites include mesenteric lymph node and liver ± spleen, lung, and bone marrow

Clinical Signs

•systemic illness with visceral or systemic forms: depression, anorexia, weight loss, and intermittent vomiting

Diagnosis

•splenomegaly ± peritoneal effusion for splenic MCT

•abdominal mass with diarrhea and possibly pyrexia in intestinal MCT

•mast degranulation is usually episodic with systemic mastocytosis and clinical signs include GI ulceration, uncontrollable hemorrhage, altered smooth muscle tone, hypotensive shock, and respiratory distress

•respiratory distress can also be caused by pleural effusion or anemia which is present in up to 33% of cats

•FNA of cutaneous mass, spleen, intestinal mass, or from pleural or peritoneal fluid: granules stain blue with Giemsa and purple with toluidine blue and appear more eosinophilic with hematoxylin and eosin stains

•tissue biopsy and histology required for diagnosis of histiocytic MCT

•disseminated disease: hematology, serum biochemistry, buffy coat smear, bone marrow aspirate, and coagulation profile

•anemia (33%) common in the splenic but not intestinal form due to increased splenic sequestration, red blood cell coating with antibodies, and endocytosis of red blood cells by mast cells

•cats with systemic mastocytosis will have eosinophilia, basophilia and peripheral mastocytosis (50%)

•mast cells can account for up to 25% of white blood cells in cats

•coagulation abnormalities reported in 90% of cats with splenic MCT, but rarely clinically significant

•methylated metabolites of histamine in urine may be a valuable diagnostic technique for mastocytosis

Treatment

•surgery: resection (5-10 cm margins recommended) with end-to-end anastomosis for intestinal MCT

•effectiveness of adjunctive therapy unknown

•combination chemotherapy protocols using prednisone, vincristine, cyclophosphamide, and methotrexate have not offered a survival advantage over surgery alone

Prognosis

•poor prognosis as most cats die or euthanased soon after diagnosis

•solitary intestinal MCT without metastasis may have prolonged survival following end-to-end anastomosis

•MST 199 days for cats with colonic MST