In recent years, considerable progress has been made in understanding the role of the immune system in tumour progression. However, in canine mammary tumours (CMT), the prognostic value of T-lymphocytes is not established. The aims of the present study were to characterize T-lymphocytic infiltrate in 57 canine mammary tumours (21 benign and 36 malign), by immunohistochemical detection of CD3 antigen, and to determine its association with several clinicopathological parameters and overall survival. CD3+ positive cells were counted in 10 high-power fields within the tumour (i.e. The tumour-infiltrating T-lymphocytes, TIL), in the peripheral area of the tumour and in the adnexal non-tumoural mammary gland. CD3(+) TILs were significantly more frequent in benign than in malignant tumours (p<0.001). Conversely, peripheral CD3(+) TILs were significantly more frequent in malignant than in benign neoplasias (p<0.001). For CD3(+) T-lymphocytes in the adnexal non-tumoural mammary gland, there was no statistical difference in their frequency between benign and malignant tumours. On survival analysis, there was a tendency towards an association of a higher number of CD3(+) TILs and a shorter overall survival (p=0.08). Interestingly for CD3(+) T-lymphocytes in the adnexal non-tumoural mammary gland, a statistically significant relationship was observed, with a higher number of lymphocytes conferring a reduced overall survival (p=0.045). Further studies will be required to better understand the biological implications of the current findings.
