Page 192 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Round Cell Tumours
179
Pearls and Pitfalls
VetBooks.ir • Cytologically, cutaneous histiocytoma may sometimes resemble other round cell tumours,
including large cell lymphoma and plasma cell tumour. Histopathology and immunohis-
tochemical studies may help to provide a definitive diagnosis.
• Regressing cutaneous histiocytoma is accompanied by a progressive lymphocytic infiltrate
(CD8+ T-cells). In the later stages, this may be difficult to differentiate from a cutaneous small
cell lymphoma. In these cases, molecular clonality testing (PARR) might be considered to assist
in the diagnosis. However, clonal T-cell expansions have been documented in association with
the cytotoxic T-cell response to histiocytoma.

Fig. 10.9. Dog. Cutaneous histiocytoma. Wright-Giemsa.

Fig. 10.10. Dog. Cutaneous histiocytoma. The cytoplasm of the histiocytes is lighter than the surrounding back-
ground. Wright-Giemsa.