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 tissue samples of 39 neoplasms of the skin and subcutaneous tissues of the dog 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 cell proliferation. The correlation between the apoptotic index (AI), the percentage of positive cells after randomly enumerating 1000 cells and the mitotic count (MC), the number of mitotic figures in 10 fields at a magnification of 400 times was assessed by the Spearman non-parametric correlation test. 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 in benign rumours, while no correlation was found between AI and Me in either malignant or locally invasive tumours. Among benign tumours, intracutaneous cornifying epithelioma, fibroma, haemangioma and Schwannoma had high AI and low Me, while histiocytomas had low AI and high Me and pilomatrixomas low AI and MC. All malignant tumours had low AI and high MC, except for fibrosarcomas, which had high AI and MC. Finally, higher heterogeneity was observed among locally invasive rumours, as they had high AI and low MC (squamous cell carcinomas), and low AI with either low MC (haemangiopericytomas) or 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.