Immunocytochemical detection of the class A macrophage scavenger receptor CD204 using air-dried cytologic smears of canine histiocytic sarcoma.

Abstract

Cytologic diagnosis of canine histiocytic sarcoma (CHS) can be challenging because neoplastic histiocytes commonly show marked nuclear and cellular atypia and may resemble other pleomorphic malignant round cell tumors. Therefore, even on histopathologic examination, immunostaining is often necessary for a definitive diagnosis. The objective of this study was to validate an anti-human CD204 antibody for immunocytochemical staining of air-dried smears for a rapid definitive diagnosis of CHS. Cytologic specimens were obtained from 10 dogs with CHS and 45 dogs with other tumors. After the cytologic evaluation of modified Giemsa-stained smears, acetone-fixed specimens were immunostained using mouse anti-human CD204 antibodies. All immunocytochemical specimens were assessed blinded and at high-power magnification (×40 objective) in 10 randomly selected fields per sample. Parameters evaluated were the subjective staining intensity and location, and the proportion of positive cells. All 10 CHS samples showed intense positive staining for CD204 in ≥50% of the cells, whereas the 45 other tumors were negative for CD204 staining. Immunocytochemistry of air-dried cytologic smears of CHS for CD204 is useful for a rapid confirmation of a cytologic diagnosis of CHS.