P8 is a transcription factor and its expression is elevated in response to apoptotic stimuli. However, p8 in human carcinoma tissue has not been investigated in depth. In this study, we investigated p8 expression in breast carcinoma. We immunohistochemically investigated p8 expression in 50 cases of breast carcinoma, including 7 non-invasive ductal carcinomas. High expression of p8 was observed in 60% of cases, which was inversely related to tumor size and UICC stage. All non-invasive ductal carcinomas diffusely expressed p8. Furthermore, in tumors of 2cm or larger, the p8 expression was inversely linked to the apoptotic index. These results suggest that p8 plays a role in the early phase of breast carcinoma progression and especially in tumors of larger size, acting as an inhibitor of apoptosis of breast carcinoma cells.