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.