In situ detection of DNA fragmentation and expression of bcl-2 in human neuroblastoma: relation to apoptosis and spontaneous regression.

Abstract Spontaneous regression occurs in some cases of neuroblastoma, especially stage IVS. The incidence of neuroblastoma has been reported to be increasing since the mass screening program was introduced in Japan. This would indicate that the screening is detecting regressing tumors. However, the mechanism of regression is still unknown. To evaluate the hypothesis that the regression might be related to apoptosis, the authors examined apoptosis by in situ end-labeling of fragmented DNA and expression of the apoptosis-suppressing protein bcl -2. Materials and Methods: One hundred eighteen neuroblastoma cases were available for examination. Eighty (67.8%) were detected by the mass screening program. Serial sections were cut from paraffin-embedded tumors. A modified TdT-mediated dUTP nick end-labeling (TUNEL) method was performed to detect apoptosis. Immunohistochemical analysis was performed to detect bcl -2 expression. Results: In cases under 1 year of age or with a favorable clinical stage, the incidence of apoptosis was significantly high. Expression of bcl -2 was associated with N- myc amplification and unfavorable histology (Shimada classification). Tumors in patients under 1 year of age often had areas where cellularity was markedly decreased, and apoptosis was often observed while bcl -2 expression was reduced. In such cases, there was a negative correlation between occurrence of apoptosis and bcl -2 expression. This suggests that apoptosis may be related to spontaneous regression in neuroblastoma.