Detection of DNA Fragmentation in Human Breast Cancer Tissue by an Antibody Specific to Single-stranded DNA

While there have been many reports concerning the clinical significance of bcl-2 expression in human breast cancer, little is known about apoptosis in primary breast cancers. We immunohistochemically examined DNA fragmentation in 107 primary human breast cancers from Japanese women using an antibody specific to single-stranded DNA. The apoptosis index calculated as the product of the positive cell number and the cellularity coefficient, ranged from 0 to 48. The average incidence of apoptosis was calculated as 0.1% of tumor cells. No relationships were observed among the apoptosis index, expression of bcl-2, and the histological grade of the tumors. Almost all apoptotic cells were phagocytosed by surrounding tumor cells immediately after DNA fragmentation. Apoptotic body formation was rare. The apoptotic cells seemed to be degraded within phagocytes, leaving no trace of apoptosis except the tiny shells of nuclei. The intensive phagocytic reaction might be one of the main reasons for the low incidence of apoptosis in human breast cancers.