Molecular-genetic markers for diagnosis and prognosis in pediatric solid malignancies
N.M. Khranovska, N.V. Ionkina, N.M. Svergun, M.V. Inomistova, G.I. Klymnyuk
National Cancer Institute, Kyiv, Ukraine
Introduction: Molecular-genetic markers are very important tools for diagnosis and prognosis of solid tumors in children. Aim: To study chromosomal translocations in patients with pediatric solid malignancies. Patients and Methods: Study has been performed on 279 tumor specimens, which were collected at diagnosis, and 90 specimens of bone marrow (BM) puncture biopsy from 200 patients with neuroblastoma (NB), 21 — Ewing sarcoma family tumors (ESFT), 29 — alveolar rhabdomyosarcoma (ARMS), 29 — embryonal RMS (ERMS). The study protocol was approved by Ethical Committee permission of National Cancer Institute (Kyiv, Ukraine). Chromosomal translocations were detected by fluorescence in situ hybridization (FISH) or real-time PCR on fresh or paraffin-embedded tissue samples. Results: Chromosomal translocation t(2;13)(q35;q14) exhibiting chimeric PAX3-FKHR and PAX7-FKHR gene products are the hallmarks of the ARMS. PAX-FKHR fusions were detected in 58 RMS samples: 10 (17,3%) had PAX3-FKHR and had 24 (41,4%) PAX7-FKHR fusions, 24 (41,3%) cases were fusion-negative. PAX3-FKHR or PAX7-FKHR fusions were found in all ARMS. PA3/7-FKHR was detected in 5 of 29 patients with eRMS; it indicates the type of mixed type RMS and requires a change of tactics on the protocol for the treatment of ARMS. In addition, PAX3-FKHR fusion products were detected in biopsy tissue and BM from 3 patients. ESFT is associated with chromosomal translocation t(11;22)(q24;q12). Out of the 21 samples with translocations detected, 16 (76.3%) had EWS-FLI1 type 1, 1 (4.7%) had EWS-FLI1 type 2, 2 (9.5%) had EWS-ERG, 2 (9.5%) had EWS-ETV4 translocation. Fusion transcript EWS-FLI1 type 1 was found in BM of 6 patients. The most significant abnormality in NB is amplification of proto-oncogene MYC; its locus lies on the short arm of chromosome 1. In 44 (22%) cases of primary NBs amplification of MYCN gene is present. MYCN gene is a factor of unfavourable prognosis and influences the choice of treatment schedules. One sample with MYCN amp pos and 1p36 del pos, and 3 samples in MYCN amp neg and1p36 del pos were detected. Loss of heterozygosity (LOH) at 1p36 was independently associated with a worse outcome in NB patients. NB expresses the tyrosine hydroxylase (TH) mRNA, the first enzyme in the catecholamine pathway. TH expression was found in BM of 74 (37%) patients with NB. Molecular-genetic testing is more accurate than standard morphological methods; it enables detection of the presence of tumor cells in BM at diagnosis and during treatment, allows optimization of the treatment strategy. Conclusion: Molecular-genetic analysis helps to identify specific genes in children with solid malignancies in order to specify the diagnosis, prognosis; it also influences the selection of at-risk patients and treatment monitoring.
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