+ 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
  • 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