Evidence of apoptosis in neuroblastoma at onset and relapse. An analysis of a large series of tumors.

Neuroblastoma (NB) is a tumor of pediatric age that is associated with high mortality in metastatic stages, although stage IVS patients undergo frequent spontaneous regression. Since apoptosis has been proposed as a possible cause of remission among cancer patients, we tested this hypothesis among both localized and metastatic NB and, in particular, NB metastatic stage IVS. We have assayed 36 localized and 117 metastatic neuroblastomas for evidence of internucleosomal DNA degradation and confirmed DNA fragmentation by the flow cytometric Terminal deoxynucleotidyl Transferase method, which also allowed us to measure DNA content and cell cycle phases. These techniques provided evidence of apoptosis in 18 out of 153 samples (11.8%), that were equally distributed among all stages except IVS, i.e. 11.1% in stage I (2/18), 11.1% in stage II (2/18), 13.2% in stage III (5/38), 13.4% in stage IV (9/67), and 0% in stage IVS (0/12). Tumor tissue samples collected at onset and also at relapse for the same patients showed that apoptosis may occur at relapse. In addition, cells appear to undergo apoptosis independently from N-myc amplification, cell cycle phase and DNA ploidy. In conclusion, apoptosis seems to take place with about an equal frequency for both favourable and unfavourable stages with an exception for IVS. Since DNA fragmentation remained undetected in stage IVS, we suggest that apoptosis is not a mechanism of spontaneous regression for these patients. A better basic understanding of the complex molecular mechanisms and biochemical pathways that control apoptosis in neuroblastoma appears to be necessary.