Spontaneous programmed cell death in infiltrating duct carcinoma: association with p53, BCL-2, hormone receptors and tumor proliferation

Recent evidence has emphasized the importance of programmed cell death or apoptosis in the maintenance of tissue homeostasis and pathogenesis of tumors. This study, analyzed in breast cancer, investigates the significance of apoptosis in relation to the expression of p53 and bcl-2 proteins, tissue proliferation defined by Ki-67 expression, hormone receptors and tumor grade. The extent of apoptosis was defined by morphological criteria and the TUNEL (Tdt-mediated dUTP biotin nick end labelling) assay. Immunocytochemistry was performed for p53, bcl-2, estrogen receptor, progesterone receptor and Ki-67 expression. Mutant p53 protein was detected using a mutant specific ELISA. Immunoreactivity of p53 significantly correlated with the presence of mutant p53 protein detected by ELISA (r = 0.654, p = 0.00001). An inverse correlation was observed between bcl-2 expression and the extent of apoptosis (r = -0.33369, p = 0.01912). The extent of apoptosis directly correlated with p53 protein accumulation (r = 0.485, p = 0.00041), Ki-67 immunoreactivity (r = 0.435, p = 0.001), histopathological grade (r = 0.492, p = 0.0003), tumor size (r = 0.326, p = 0.023) and lymph node status (r = 0.287, p = 0.047). A direct correlation was also observed between p53 expression and Ki-67 immunoreactivity (r = 0.623, p = 0.0002). There was no statistically significant association between estrogen and progesterone receptor status and apoptosis. In addition, the TNM stage of the disease correlated with immunoreactivity of p53 (r = 0.572, p = 0.00012) and Ki-67 (r = 0.3744, p = 0.00818). Bcl-2, by inhibiting apoptosis, may cause a shift in tissue kinetics towards the preservation of genetically aberrant cells, thereby facilitating tumor progression. These results imply that rapidly proliferating tumors appear to have a high "cell turnover state" in which there may be an increased chance of apoptosis amongst the proliferating cells. The ability of apoptosis to also occur in the presence of mutant p53 protein suggests the existence of at least two p53-dependent apoptotic pathways, one requiring activation of specific target genes and the other independent of it.