Author reply

Abstract

We thank Matsumura et al. for their interest, comments, and insightful investigation. Matsumura et al. have already established the cell line from the metastatic foci of a neuroblastoma case, investigated the biologic characteristics by using molecular biologic techniques, and demonstrated evidence of the cytogenetic heterogeneities in neuroblastoma.1, 2 In addition, as they mentioned in their correspondence, they reported the neuroblastoma case showing the clonal evolution in vivo. The concept of clonal evolution or selection during the accumulation of genetic aberrations of the neuroblastoma is very important in considering the natural history of the tumor. We have the same hypothesis regarding the study of the histopathologic characteristics of neuroblastomas.3 Especially in cases detected through a mass screening system, we often find distinct heterogeneity of the histology and the undifferentiated foci in the favorable histology, as we demonstrated in our report.4 Whether or not any minor focus or foci of tumor tissue with N-myc amplification were present in the original tumor is an interesting and important question. However, there has not been any distinct evidence of clonal evolution or selection in our case, and we are investigating both the frozen tissue and the paraffin-embedded tissue of the original tumor to compare with the biologic properties of our cell line (MASS-NB-SCH-1) by fluorescence in situ hybridization. However, we are not yet quite satisfied with the results of the experiment so far, with respect to whether the tumor tissue taken for cultivation is different from the preserved primary tumor tissue. It is not apparent whether the primary tumor cells with similar properties to the cultivated cells are included in the rest of the tissues or not, even if the original tumor had a distinct heterogeneous property. It is suggested in general that some chromosomal aberrations would occur during the establishment of a cell line in vitro. Meanwhile, we have considered N-myc copy number to be a stable marker,5 indicating that the amplification would occur relatively early in tumorigenesis.6 If there were no unfavorable foci with N-myc amplification in the original tumor, it might be suggested that some clonal evolution had emerged in vitro. We think that any finding of a distinct heterogeneity or clonal selection might be incidental and dependent on the phase of tumorigenesis at the time the tumor tissue was removed. It was reported that a case of rhabdomyosarcoma, which did not have N-myc amplification at diagnosis, showed 10-fold amplification at relapse.7 Neuroblastomas de-tected through a mass screening system are in general diagnosed when the patient is age 6 months regardless of clinical symptoms. Although that is no more than a speculation, some neuroblastomas detected through a mass screening system might be in the early phase of tumorigenesis. The cultivated cells from Matsumura's case with metastatic lesions would be in a later phase of tumorigenesis of neuroblastoma than the usual lesions detected through a mass screening, and the clonal selection or evolution might already be terminated. Needless to say, the more the heterogeneity of the neuroblastoma is involved with clonal evolution or selection, the more important it is to analyze the biologic characteristics using molecular biologic techniques. Furthermore, we think that investigation of the cases detected through a mass screening could reveal the mechanism of the tumorigenesis of neuroblastoma, with respect to amplification of the N-myc gene, chromosome 1p deletion, and so on. Hisayuki Hiraiwa M.D.*, Minoru Hamazaki M.D.