Chromosomes and screening for neuroblastoma

Neuroblastoma: biological insights into a clinical enigma

Neuroblastoma is a tumour derived from primitive cells of the sympathetic nervous system and is the most common solid tumour in childhood. Interestingly, most infants experience complete regression of their disease with minimal therapy, even with metastatic disease. However, older patients frequently have metastatic disease that grows relentlessly, despite even the most intensive multimodality therapy. Recent advances in understanding the biology and genetics of neuroblastomas have allowed classification into low-, intermediate- and high-risk groups. This allows the most appropriate intensity of therapy to be selected - from observation alone to aggressive, multimodality therapy. Future therapies will focus increasingly on the genes and biological pathways that contribute to malignant transformation or progression.

Detection of N-myc amplification by FISH in immature areas of fixed neuroblastomas: more efficient than Southern blot/PCR

N-myc amplification is a major prognostic factor in neuroblastomas and is systematically investigated by Southern blot or polymerase chain reaction (PCR). A retrospective study of N -myc amplification has been carried out using fluorescence in situ hybridization (FISH) in 97 fixed neuroblastomas. For each tumour, FISH was performed on the area that contained the most immature neuroblasts. Among these 97 neuroblastomas, 16 were amplified and 12 were not interpretable. FISH was not interpretable in six cases. All neuroblastomas with N-myc amplification detected by Southern blot/PCR were amplified with FISH, except three that were not interpretable. Four tumours that were not interpretable in Southern blot/PCR contained more than five copies of N-myc by FISH: one was aneuploid and three were truly amplified, containing more than ten copies of N-myc. Among these three patients, two died in a short time of their tumours. Ten cases were not amplified by Southern blot/PCR and showed more than five copies by FISH: four were aneuploid and two showed heterogeneous amplification, with a few cells clearly amplified whereas most were not. Four cases were amplified, of which two patients died of their tumours. This study confirms that when applied to the most immature areas of fixed neuroblastomas, FISH displayed a higher sensitivity than molecular techniques (p < 0.001) and could detect heterogeneous amplification. FISH could therefore become an important complementary procedure in assessing prognosis in neuroblastomas.

Is there a future for neuroblastoma mass screening?

It is apparent that mass screening at the age of six months in Japan detects significant numbers of otherwise spontaneously regressing tumors. Nishi et al. estimated that at least 50% of tumors detected by screening with the HPLC method would otherwise regress spontaneously [31]. Considering that not all patients found by screening who were treated and survived required therapy to obtain that result, the proportion of spontaneously regressing NBLs would be even larger. Nobody can deny that screening at the age of six months detects some tumors that would otherwise be found clinically later on. Indeed, our data show that screening led to some decrease in incidence at the age of 3 years [10]. However, this study also showed that the tumors detected by screening would, if not picked up on screening, have grown very slowly over 3 years. That is, they were not rapidly progressing tumors. There is evidence showing that evolution from tumors with favorable biologic features to tumors with unfavorable ones is unlikely [32], while no convincing example of such evolution has been reported.

Neuroblastoma mass screening: the arguments for and against

Neuroblastoma is the second commonest malignancy in childhood. The prognosis of the disease is largely dependent on the extension of the tumour at diagnosis. For disseminated disease the survival rate is very low. The question as to whether mass screening in infants can improve the prognosis of the disease was first addressed in Japan more than 20 years ago. Since then, more than 7 million children have been screened in Japan and over 650 cases of neuroblastoma have been detected. However, the available data are compromised by an inadequate cancer registry and conclude that screening at 6 months of age seems to double the incidence of neuroblastoma. This result has been verified by a Canadian study conducted from 1989 to 1994 in the province of Quebec. The incidence of neuroblastoma appeared to have tripled, and there was no decrease in the rate of advanced disease. Mass screening pilot studies have also been conducted in the U.K., France, Austria, Australia, U.S.A., Italy, Norway and Germany. Analysis of the results shows that neuroblastoma screening before the age of 6 months is feasible, but no significant reduction in mortality could be shown until now. Moreover, most of the cases diagnosed by screening have favourable biological markers. Only a few with unfavourable parameters, such as amplification of proto-oncogene MYCN, diploidy and/or del 1p36 could be detected. A screening programme that includes 1.25-2 million screened and unscreened children at 1 year of age monitored by an almost complete national cancer registry should show whether mass screening for early detection of neuroblastoma is worthwhile.

Clinical impact of chromosome 1 aberrations in neuroblastoma: a metaphase and interphase cytogenetic study

Neuroblastoma tumors are characterized by aberrations of chromosome 1. Rapid detection of these chromosomal aberrations at diagnosis could give important clues to outcome and therapy. We attempted to detect numerical and structural aberrations of chromosome 1 not only by classical metaphase cytogenetics but also by interphase cytogenetics in order to overcome difficulties of karyotyping due to diminished metaphase quality and quantity in primary neuroblastoma samples. Karyotypic changes of chromosome 1 in 53 primary neuroblastomas were evaluated. In addition, we successfully performed interphase cytogenetics using single and double in situ hybridization procedures with chromosome 1-specific repetitive DNA probes on nuclei preparations obtained from 46 and 20 tumors, respectively. Polysomies of structurally normal chromosomes 1 were predominantly seen in tumors with good prognosis, whereas deletions of 1p material were nearly exclusively confined to progressive tumors. Numerical and structural chromosome 1 aberrations as studied by metaphase and interphase cytogenetics are thus valuable prognostic markers in neuroblastoma.

Mass screening in Japan increased the detection of infants with neuroblastoma without a decrease in cases in older children

Analysis of data from the Kanto-Ko-Shin-Etsu Branch of the Japan Children's Cancer Registry revealed that mass screening for neuroblastoma increased the detection of cases in infants younger than 1 year from about 25% before screening to about 50%, and the percentage of neuroblastomas among all pediatric cancers almost doubled, from approximately 10% to 19.3%. However, when the cases found on screening were subtracted, the numbers after the onset of mass screening were similar to those before screening. It is likely that neuroblastoma mass screening has identified a unique type of tumor, which may not be recognized without mass screening, rather than that it has contributed to the earlier diagnosis of tumors in older children.

Morphological and cytogenetic characterization and N-myc oncogene analysis of a newly established neuroblastoma cell line

A permanent cell line established from a xenograft of neuroblastoma which occurred in a 5-year-old girl was investigated for its morphological and biological characteristics. The cultured cells were tumorigenic in nude mice. Microscopically, each tumor consisted of small round to polygonal cells with irregular nuclei and prominent nucleoli, corresponding to the features of the primary and xenografted tumor cells. Electron microscopic examination revealed that both the transplanted tumor cells and the cultured cells contained scanty microtubules and dense-core neurosecretory granules. Chromosome analysis of this cell line showed monosomy for chromosomes 1, 10, 19 and X, and structural rearrangements involving chromosomes 8, 17 and 20, in addition to numerous double minutes. The N-myc oncogene was found to be amplified 40- to 80-fold in the transplanted and cultured tumor cells, as well as in the primary tumor cells. In situ hybridization with a digoxigenin-labeled uridine-triphosphate N-myc RNA probe detected abundant mRNA in the tumor cells. This neuroblastoma line may become a valuable in vitro experimental model system for studies aimed at better characterization of neuroblastoma.

Chromosomal changes in renal cell carcinoma. No evidence for correlation with clinical stage

A cytogenetic study was performed in 18 renal cell carcinomas using a culture method previously described. The significance of chromosome involvement in clonal aberrations was evaluated according to the mean + 1 SD objective criterion. Chromosomes 3, 7, 9, and 17 were preferentially involved in both numerical and structural changes. The cytogenetic data have been correlated with the clinical staging, but in contrast to a previous study, abnormalities of chromosome 3 were not associated with a higher clinical stage.

Problems of mass screening for neuroblastoma: analysis of false-negative cases

The Japanese mass screening (MS) system for neuroblastoma at 6 months of age has resulted in the earlier diagnosis of the tumor with excellent therapeutic results. However, some problems are involved in the present MS system. We present six false-negative cases, ages ranging from 1 year 11 months to 3 years 11 months. Neuroblastoma cell taken from four of these patients were studied biologically. These patients had advanced disease (one was stage III; five were stage IV). Three of the patients have died and one is terminally ill despite undergoing surgery combined with intensive chemotherapy. Cytogenetic analysis performed in three cases showed that all the cases had diploid chromosome mode associated with 1P-, double minutes (DMs), or marker chromosomes. N-myc oncogene analysis, performed in four cases, showed amplification in two; one patient had diploid chromosomes, but the other was not examined cytogenetically. These findings were strikingly different biologically from those of cases found by MS. The majority of neuroblastomas detected by MS were found to be triploid tumors without N-myc amplification. These findings suggest that the main reason for the false-negative results in the patients we examined is that they were tumor-free or the tumors were so small in size that they were unable to produce urinary vanillylmandelic acid and or homovanillic acid levels high enough to be detected at the time of MS. Therefore, we conclude that MS at 6 months of age is too early to detect neuroblastoma with a diploid chromosome mode and/or amplified N-myc oncogene. We propose that MS at the age of 1 year 6 months would be more effective to pick up these cases, because treatment strategies depend on the different biological characteristics of tumor cells.

A comparative analysis of nuclear DNA content and N-myc gene amplification in neuroblastoma

Nuclear DNA content and N-myc amplification have been found to have prognostic significance in neuroblastoma. To investigate the interrelationships between these two parameters, tumor samples from 18 patients with neuroblastoma were analyzed for both total DNA and N-myc gene content. Quantitative DNA analysis was performed by image analysis. Quantitative Southern blot hybridization was used to determine N-myc gene copy number and to distinguish between low level gene amplification or excess gene copies secondary to aneuploidy. Six of the 18 patients have died. Five of the six had nonaneuploid tumors, but only two of the six exhibited major N-myc amplification. Low-level amplification was detected in one Stage II patient. The authors' results suggest that neuroblastomas with N-myc amplification are a subset of nonaneuploid tumors.

How frequent is spontaneous remission of neuroblastomas? Implications for screening

The 'true' incidence of spontaneous regression of neuroblastomas is uncertain. However, the frequency of spontaneous regression is important when the benefits of screening procedures are considered. In the population-based Danish neuroblastoma survey 1943-80, spontaneous regression was documented in less than 2% of cases. However, the 'true' incidence may be higher. The epidemiological findings of increased incidence and survival rates with an unchanged mortality rate may suggest the inclusion of borderline lesions among 'truly' malignant neuroblastomas in recent decades in Denmark. However, it is more likely to be a result of improved diagnosis, changes in the social composition of the population and possibly unidentified environmental agents. However, if some premalignant lesions in fact had been included, they are most likely to be stages I-II tumours of infancy. In this study we describe cases of spontaneous regression of neuroblastoma from the Danish population-based survey 1943-80.

Flow cytometry DNA ploidy analysis and catecholamine secretion profiles in neuroblastoma

Previous studies have shown that catecholamine secretion patterns have been imperfect predictors of clinical behavior of neuroblastomas. Recently, studies of nuclear DNA content in neuroblastoma have shown that an aneuploid DNA content predicts favorable clinical behavior. To determine if a correlation exists between these tumor biologic indicators, the authors analyzed both in a series of 39 patients with neuroblastoma. Flow cytometric DNA analysis performed on paraffin blocks determined that 23 patients had tumors with aneuploid DNA content (aneuploid tumors) and 16 patients showed no demonstrable anomalies of tumor DNA content (nonaneuploid tumors). Comparison of catecholamine levels in urine and tumor homogenates with DNA content data indicate that nonaneuploid neuroblastomas include a significant number (P less than 0.02) of biochemically primitive tumors which secrete high levels of 3,4 dihydroxyphenylalanine (DOPA), dopamine and homovanillic acid (HVA). This suggests a dopamine-norepinephrine pathway block, which supports previous reports of deficiency of dopamine beta-hydroxylase activity in some neuroblastomas. The study shows that in contrast to aneuploid tumors, nonaneuploid neuroblastomas secrete higher levels of early pathway catecholamine metabolites and are more likely to present in higher (unfavorable) clinical stages of disease.

The chromosomal analysis of human solid tumors. A triple challenge

The present review considers the three main issues of the cytogenetic analysis of human solid tumors: the technical limitations, the difficulty in interpreting the available results, and the uncertainty affecting any hypothesis about the role of chromosome changes in tumorigenesis. Information is given on the recent improvements in the field of tumor cell culturing and karyotyping, with a critical discussion of more than 1300 cytogenetic studies from 18 different tumors, and clues for a synthetic understanding of the cytogenetics of malignancy.