The peripheral neuroblastic tumour group includes NBL, GNBL and GN. NBL is the most common extracranial solid tumour of childhood and the incidence of pediatric neuroblastoma are increasing
[17, 18]. MYCN gene amplification is a known molecular marker for aggressive progression of NBL
. In the study, we evaluated the histological presentation and MYCN gene copy number in 220 pediatric neuroblastic tumors, which include 178 NBLs, 32 GNBLs and 10 GNs and analyzed their association with clinical outcome of the patients. To our knowledge, this is the first article for MYCN gene and chromosome 2 aneusomy analyses by using fluorescence in situ hybridization (FISH) method in chinese pediatric patients.
Our study reaffirmed the need for MYCN copy number to be determined in light of chromosome 2 copy number. MYCN copy number had been determined by southern blot analysis
. After 1993, fluorescence in situ hybridization (FISH) was used to determine the presence of MYCN amplification
[20, 21]. In these studies, the results of southern blotting and FISH analysis were prospectively compared and a MYCN copy number of ≥ 10 was determined to be the optimal cutoff by FISH
, as the vast majority of amplified tumors have very large numbers of double minutes in each tumor cell. By southern blotting, any normal cells in the tissue were included in the measurement, whereas by FISH, each tumor nucleus was visualized directly and simultaneous cohybridization with a specific chromosome probe is of great value in predicting the prognosis of patients
. FISH has a higher sensitivity because it detects the MYCN copy number on the single-cell level and allows correlation of morphologic details. In our estimation, FISH is a practical, useful and reliable method for analysis of MYCN copy number in neuroblastic tumors.
Our results showed that aberrant MYCN copy number was detected in 153 (85.9%) of 178 NBLs, with amplification constituting 24 (13.5%), gain 129(72.4%). In contrast, MYCN amplification is only observed in one GNBL case (1/32, 3.1%) and no GN cases (0/10, 0%). Moll A et al.
 also reported that no amplification of the MYCN-oncogene was found in mixed hepatoblastoma and teratoma of the liver in a 3-year-old boy. Wan,T.S et al.
 investigated 12 NBL patients for MYCN amplification by FISH and found that 16.7% cases had MYCN amplification. Angelini,P et al.
 reported that only about 2% had MYCN gene amplified tumours in 232 GNBL patients. Our results also showed that the frequency of MYCN gene gain was significantly higher in GNBL (78.1%, 25/32) and NBL (72.5%, 129/178) than in GN (40.0%, 4/10). Toraman,A.D et al.
 found that chromosomal gains displayed by chromosomes and chromosome loci were 2p25 approximately pter (60%) in five GNBL cases by comparative genomic hybridization. Truong LN et al.
 also detected MYCN oncogenes in malignant brain tumors by using multiplex ligation dependent probe amplification (MLPA). Thus, higher frequency of MYCN gene aberrations in undifferentiated or less differentiated tumors indicates an important function of MYCN gene in tumor malignancy.
MYCN amplification is an established marker indicating aggressive tumor progression of NBL
. Our data also showed that MYCN amplification is correlated with decreased overall survival in NBL (P=0.017) (Figure
3A). More significantly, we demonstrated for the first time that the presence of extra copies of MYCN gene is an independent prognostic factor for NBL in our case series. The patients with MYCN gene gain had a significantly longer mean survival time than those with normal MYCN gene copy number (P=0.012) (Figure
3B). In our data, NBL cases with MYCN gene gain also showed gain of centromere 2, suggesting polyploidy in these cases. In 1991, look et al.
 found that NBL patietns treated with cyclophosphamide-doxorubicin, hyperdiploidy was closely associated with long-term disease-free survival (greater than 90% of cases), while diploidy invariably predicted early treatment failure (P <0.001). Recently, George et al. had also found that NB patients with hyperdiploidy plus no amplified MYCN confers a favorable prognosis
, which is in line with our study. Furthermore, they also found that hyperdiploidy plus no amplified MYCN NBL patients may respond well to contemporary chemotherapy, and could be spared intensive myeloablative therapy with stem-cell rescue
. Thus, the classification of MYCN gene status as three groups by FISH may provide more powerful prognostic indicator and better treatment options in NBL.