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

Abstract

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.TUNELsignals were observed in all types of tumours 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 betweenAIandMCwas observed in benign tumours, while no correlation was found betweenAIandMCin either malignant or locally invasive tumours. Among benign tumours, intracutaneous cornifying epithelioma, fibroma, haemangioma and Schwannoma had highAIand lowMC, while histiocytomas had lowAIand highMCand pilomatrixomas lowAIandMC. All malignant tumours had lowAIand highMC, except for fibrosarcomas, which had highAIandMC. Finally, higher heterogeneity was observed among locally invasive tumours, as they had highAIand lowMC(squamous cell carcinomas), and lowAIwith either lowMC(haemangiopericytomas) or highMC(basal cell tumours). The classification of the tumours according to theirAI(>15·8% high and <15·8% low) andMC(>9 high, <9 low) did not reflect the clinical behaviour of some tumour types.