Telomerase activity distinguishes between neuroblastomas with poor prognosis
C. Poremba
1
3
H. Willenbring
0
1
3
B. Hero
1
3
H. Christiansen
1
3
K.-L. Schafer
1
3
C. Brinkschmidt
1
3
H. Jiirgens
1
2
3
W. Bocker
1
3
B. Dockhorn-Dworniczak
1
3
0
Department of Pediatrics
1
'Gerhard-Domagk-Institute of Pathology
2
Department of Pediatric Hematology and Oncology, University of Minister, Germany; Departments of Pediatric Hematology and Oncology, ~ University ofKoln, and University of Marburg
,
Germany
3
B. Dockhorn-Dworniczak, MD, PhD Gerhard-Domagk-Institute of Pathology Westfalische Wilhelms-University Domagkstrasse
17 48149 Minister
Germany
Summary Background: Treatment of neuroblastoma has remained a major challenge in pediatric oncology because the assessment of the individual prognosis, particularly in disseminated disease is still obscure. Previous studies have correlated clinical outcome with activity levels of telomerase, a cellular reverse transcriptase which has been detected in the majority of human malignant tumors. Patients and methods: In this blind-trial study, a non-radioactive telomeric repeat amplification protocol (TRAP) with an internal telomerase-assay standard was used on an automated laser fluorescence sequencer for the detection and semiquantitative analysis of telomerase activity (TA) in 67 neuroblastomas of all clinical stages from the German Neuroblastoma Trial and 2 ganglioneuromas. TA levels were correlated with event-free and overall survival rates and established prognostic markers such as MYCN. Results: TA was present in 14 of 69 (20%) samples, including 3 of 22 stage IVS, 8 of 14 stage IV, 1of 10 stage III, 1of 7 stage II and 1of 14 stage I neuroblastomas and 0 of 2 ganglioneuromas. We found a strong statistical correlation between the presence of TA and poor clinical prognosis with regard to all tumor stages. Multivariate analysis revealed TA as an independent prognostic marker. In particular, the analysis of TA in IVS neuroblastomas distinguished two different prognostic groups. Conclusions: Our data suggest that TA is an independent prognostic marker in neuroblastoma which, in combination with other markers such as MYCN, may proof useful in assessing the individual patient's prognosis.
Introduction
Neuroblastoma represents the most common solid
extracranial neoplasm of infancy and childhood,
accounting for about 7% of all childhood cancers. The
most significant predictors of outcome are age and
stage, although an assessment of the patient's prognosis
solely on the basis of clinical parameters is limited due
to diverse biological tumor behavior and subsequent
survival rates, even at distinct clinical stages [1]. The
heterogeneity of this tumor entity requires cellular and
molecular markers in order to distinguish the different
biological characteristics. MYCN copy number and loss
of heterozygosity for Ip3236 predict poor outcome in
all age and stage groups [2-4]. Telomerase activity (TA)
has been shown to be a strong indicator of cellular
malignancy in virtually all malignant tumors, including
neuroblastoma [5, 6]. Telomerase describes a
ribonucleoprotein polymerase which uses an internal RNA
component as a template to synthesize telomeric DNA directly
onto the ends of chromosomes [7, 8]. These repetetive
sequences are considered to be important in the
protection and replication of chromosomes. Cells without
telomerase activity display progressive shortening of
telomeric repeats with each cell division, because
lagging-strand DNA synthesis at the very end of linear
chromosomes cannot be completed, a phenomenon
generally referred to as the end-replication problem [9-11].
Telomere shortening contributing to genetic instability
is believed to be the primary signal for senescence
mediated by tumor suppressor genes, such as p53 and
Rb [12-15]. Induction of telomerase activity in cells that
have bypassed this control mechanism could give rise to
clonal immortality by compensating for the loss of
telomeric DNA and thus maintaining telomere length
[16-19]. Telomere length has not proven to be a good
indicator of malignancy, since both stabilization and
extension caused by mechanisms other than telomerase
activation have been reported [6, 19-23]. Previous studies
proposed that neuroblastomas with low telomerase
activity might consist of cells that completely failed to
repress telomerase activity during development, whereas
tumors with high telomerase activity are likely to be
derived from an immortalization event in a single cell
[6, 24-26]. This condition renders clinical implications,
since high telomerase activity is supposed to be
accompanied by several genetic alterations and poor prognosis,
whereas low or even absent telomerase activity in
neuroblastomas coincides with good prognosis, and eventually,
spontaneous regression [6, 26]. Exact prognostic
implications on the basis of this two-entity model have so far
been hampered by insufficient distinction of activity
levels due to positivity for telomerase activity in the vast
majority of neuroblastomas [6, (...truncated)