The diagnosis of tumours in children

Determining if there exist genetic alterations that can be associated with the diagnosis and prognosis of neuroblastic tumours, responsible for 15% of child deaths due to cancer, was the aim of the Paula Lázcoz Ripoll’s PhD thesis which she recently defended at the Public University of Navarra. The work was entitled: Molecular diagnosis of neuroblastic tumours: genetic profile and analysis of tumour suppressor genes.

Genetic alterations

Neuroblastic tumours are malignant extracraneal tumours most frequent in infancy: they affect 1 in every 8,000 children. Amongst these tumours are ganglioneuromas, ganglioneuroblastomas and neuroblastomas, the latter being the most malignant. According to the authoress of the thesis, in some cases, treatment is not required and they revert to their original state. But there are other neuroblastomas that are more aggressive and require an excision of the tumour and the subsequent treatment with radiotherapy and chemotherapy, although with scant percentage of success.

In this context, Ms Paula Lazcoz put forward as the objective of her PhD an attempt, from a molecular pathology perspective, at the diagnosis and prognosis of neuroblastic tumours. To this end, 45 neuroblastic tumours were analysed and 12 cellular lines of neuroblastoma, i.e. cells extracted from this type of tumour and maintained in culture.

Also, eight tumour suppressor genes that appear altered in numerous types of cancer were studied. In concrete, the genes involved are PTEN, DMBT1, MGMT, FGFR2, MXI1, RASSF1A, NORE1A, BLU and CASP8. According to Paula Lazcoz, in normal conditions, the tumour suppressor genes avoid a normal cell transforming into a tumorous cell and thus giving rise to a tumour, and so the alteration of any of these genes could be involved in the genesis of a tumour.

In this way, the corresponding DNA was obtained from the tumours and the indicated cellular lines, in order to subsequently determine the frequency of homozygotic delections, loss of heterozygosity, instability of microsatellites, hypermethylation of the promoter and the level of genetic expression of the previously mentioned genes, all of these being mechanisms that can inactivate the tumour suppressor genes and, thus, favour the formation of the tumour. The techniques used in order to carry out this analysis were differential PCR, standard PCR, MSP and RT-PCR. The profile of gains and losses of genetic material at a global genome level was also studied by means of CGH.

Once the genetic alterations are determined, it was observed that no statistically significant relationship existed between the genetic alterations found and the clinical-pathological data of the tumours (age, sex, tumour location, etc). According to the authoress, these results could be due to the fact that the sample, given its size, was not very representative thus begging the question that, with a wider sample, more significant data would be obtained.

Nevertheless, a statistically significant relationship was in fact observed (p<0.05) between the hypermethylation of the RASSF1A and CASP8 genes, which might suggest the need to alter simultaneously two routes of carcinogenetic control in order to obtain a neuroblastic tumour.