Apoptosis rate in malignant mammary tumours in bitches

Abstract

As the equilibrium between cell division and cell death (apoptosis) determines the growth of a tumour, the aim of the study was to evaluate the apoptosis frequency in dog mammary tumours both by the TdT-mediated dUTP-biotin nick end Libelling (TUNEL) method and by the ELISA detection of nucleosoms in cell homogenates. For that, apoptosis rates were investigated in 35 malignant tumours (16 malignant mixed tumours, 12 lobular adenocarcinomas, 3 cirrhotic adenocarcinomas and 4 myoepitheliomas) and in 10 normal mammary tissues. Whereas the apoptotic cells were found abundant and homogeneously distributed throughout the healthy breast tissues by the TUNEL method, they appeared less numerous in malignant tumours and were essentially located within mammary acini in few areas. The average amounts of nucleosoms proportional to the absorbance at 405 nm in the ELISA test in cell homogenates from malignant tumours were lower than in the healthy mammary tissues but according to the tumour type, the difference with controls was significant only for the malignant mixed tumours (P < 0.05). These results show that apoptosis rate tended globally to decrease in dog malignant mammary tumours, favouring in this way the selection and expansion of apoptosis-resistant neoplastic cells.