Apoptosis and mitosis in tumours of the skin and subcutaneous tissues of the dog

The presence of apoptotic cell death was evaluated in routinely processed t issue samples of 39 neoplasms of the skin and subcutaneous tissues of the d og using the method of terminal deoxynucleotidyl transferase (TdT) mediated deoxyuridine-5'-triphosphate (dUTP)-biotin nick end labelling (TUNEL). The degree of apoptosis was related to the frequency of mitosis, an index of c ell proliferation. The correlation between the apoptotic index (AI), the pe rcentage of positive cells after randomly enumerating 1000 cells and the mi totic count (MC), the number of mitotic figures in 10 fields at a magnifica tion of 400 times was assessed by the Spearman non-parametric correlation t est. TUNEL signals were observed in all types of rumours as brown products detected in non-pyknotic nuclei, in non-identifiable rounded structures (so -called apoptotic bodies) and occasionally in the cytoplasm, either singly or in combination. An inverse relationship between AI and MC was observed i n benign rumours, while no correlation was found between AI and Me in eithe r malignant or locally invasive tumours. Among benign tumours, intracutaneo us cornifying epithelioma, fibroma, haemangioma and Schwannoma had high AI and low Me, while histiocytomas had low AI and high Me and pilomatrixomas l ow AI and MC. All malignant tumours had low AI and high MC, except for fibr osarcomas, which had high AI and MC. Finally, higher heterogeneity was obse rved among locally invasive rumours, as they had high AI and low MC (squamo us cell carcinomas), and low AI with either low MC (haemangiopericytomas) o r high MC (basal cell tumours). The classification of the rumours according to their at (>15.8% high and <15.8% low) and MC (>9 high, <9 low) did not reflect the clinical behaviour of some tumour types.