Intestinal MCT - Feline

+ 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

Systemic illness with visceral or systemic forms:

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

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

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