Significance of mastocytemia in cats.

Background: In cats, mastocytemia is considered to be confined to animals with mast cell tumors (MCT), whereas in dogs it is associated with diverse diseases.

Objective: The objective of this retrospective study was to investigate the diagnostic and prognostic significance of mastocytemia in cats.

Methods: All blood smears and buffy coat (BC) smears on which mast cells were identified over a 6-year period were retrospectively reviewed and mast cells counted. Mastocytemic cats were classified based on their clinical diagnosis.

Results: Mastocytemia was identified on 40 blood smears and 13 BC smears from 33 cats. The incidence of mastocytemia detected in cats during routine CBCs was 0.33% (40/12,116 CBCs). Twenty-two of 33 mastocytemic cats (67%) had visceral (n = 17) or cutaneous MCT (n = 7), including 2 that had concurrent visceral and cutaneous involvement. In 3 additional cases (9%), visceral MCT was clinically suspected, but no cytologic or histopathologic evaluation of visceral organs was performed. MCT was excluded in 3 of 33 mastocytemic cats (9%) with a final diagnosis of lymphoid neoplasia (n = 2) and multiorgan hemangiosarcoma (n = 1). Five additional animals (15%) had a diagnosis other than MCT, including lymphoma (n = 2) and chronic renal failure (n = 3), but no cytologic or histopathologic evaluation of the spleen was performed. Blood smears from cats with confirmed MCT had 1-113 mast cells per smear, whereas cats in which MCT was excluded had 1-2 mast cells per smear.

Conclusions: Data confirm that mastocytemia is rare and most commonly found in cats with visceral MCT; however, rare circulating mast cells may also be seen with neoplasms other than MCT.