PATTERNS OF LYMPHOID INFILTRATE IN THE CANINE CUTANEOUS HISTIOCYTOMA

Ninety-three cases of canine cutaneous histiocytoma were examined histologically for relative amounts and patterns of intratumoural lymphocytic infiltrates. Eighteen cases (19 per cent) had a minimal, diffuse infiltrate limited to the peripheral tumour margin at the junction with normal dermis. Forty-eight cases (52 per cent) had a moderate, nodular, peripheral lymphocytic infiltrate. A marked nodular infiltrate was seen in both peripheral and central portions of the tumour in 19 cases (20 per cent), and extended from the deep tumour margin to the epithelial surface in an additional 8 cases (9 per cent). The progressive lymphocytic infiltrate was accompanied by progressive intratumoural foci of acute coagulation necrosis and other morphologically visible degenerative changes in tumour cells. It is proposed that these patterns of lymphoid infiltrate represent a morphological expression of an immune-mediated anti-tumour host response which correlate with in vivo observations of the spontaneous regression of this naturally occurring tumour in the skin of the dog. © 1979.