Early clinical evaluation of neuroblastoma cell detection by reverse transcriptase-polymerase chain reaction (RT-PCR) for tyrosine hydroxylase mRNA

A comprehensive overview of liquid biopsy applications in pediatric solid tumors

Liquid biopsies are emerging as an alternative source for pediatric cancer biomarkers with potential applications during all stages of patient care, from diagnosis to long-term follow-up. While developments within this field are reported, these mainly focus on dedicated items such as a specific liquid biopsy matrix, analyte, and/or single tumor type. To the best of our knowledge, a comprehensive overview is lacking. Here, we review the current state of liquid biopsy research for the most common non-central nervous system pediatric solid tumors. These include neuroblastoma, renal tumors, germ cell tumors, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma and other soft tissue sarcomas, and liver tumors. Within this selection, we discuss the most important or recent studies involving liquid biopsy-based biomarkers, anticipated clinical applications, and the current challenges for success. Furthermore, we provide an overview of liquid biopsy-based biomarker publication output for each tumor type based on a comprehensive literature search between 1989 and 2023. Per study identified, we list the relevant liquid biopsy-based biomarkers, matrices (e.g., peripheral blood, bone marrow, or cerebrospinal fluid), analytes (e.g., circulating cell-free and tumor DNA, microRNAs, and circulating tumor cells), methods (e.g., digital droplet PCR and next-generation sequencing), the involved pediatric patient cohort, and proposed applications. As such, we identified 344 unique publications. Taken together, while the liquid biopsy field in pediatric oncology is still behind adult oncology, potentially relevant publications have increased over the last decade. Importantly, steps towards clinical implementation are rapidly gaining ground, notably through validation of liquid biopsy-based biomarkers in pediatric clinical trials.

Opportunities and challenges of circulating biomarkers in neuroblastoma

Molecular analysis of nucleic acid and protein biomarkers is becoming increasingly common in paediatric oncology for diagnosis, risk stratification and molecularly targeted therapeutics. However, many current and emerging biomarkers are based on analysis of tumour tissue, which is obtained through invasive surgical procedures and in some cases may not be accessible. Over the past decade, there has been growing interest in the utility of circulating biomarkers such as cell-free nucleic acids, circulating tumour cells and extracellular vesicles as a so-called liquid biopsy of cancer. Here, we review the potential of emerging circulating biomarkers in the management of neuroblastoma and highlight challenges to their implementation in the clinic.

Clinical Significance of Tyrosine Hydroxylase mRNA Transcripts in Peripheral Blood at Diagnosis in Patients with Neuroblastoma

Purpose

The purpose of this study is to investigate the clinical significance of tyrosine hydroxylase (TH) expression in peripheral blood (PB) at diagnosis in patients with neuroblastoma.

Materials and Methods

TH mRNA expression in PB was measured by reverse transcription quantitative real-time polymerase chain reaction in 210 patients who were newly diagnosed with neuroblastoma from July 2005 to June 2015 and the clinical significance of TH expression in PB at diagnosis was evaluated.

Results

TH expression was positive in 60 patients (28.6%). Fifty of 60 TH-positive patients had metastatic tumors and the remaining 10 had localized tumors. TH expression was associated with high-risk features (i.e., advanced stage, older age, unfavorable pathology, and MYCN amplification) at diagnosis. Among TH-positive patients, higher TH expression level was observed in high-risk patients than in low- or intermediate-risk patients (p=0.035). The probability of 5-year progression-free survival (PFS) was lower in TH-positive patients than in TH-negative patients (63.8±6.9% vs. 94.7±2.1%, p < 0.001). In analysis confined to high-risk patients, the 5-year probability of PFS remained lower in TH-positive patients (55.7±8.2% vs. 89.6±5.8%, p < 0.001). Among TH-positive patients, a higher expression level of TH was associated with a worse outcome. In multivariate analyses, positive TH expression in PB at diagnosis was an independent poor prognostic factor for PFS.

Conclusion

The treatment intensity should be tailored according to TH expression in PB at diagnosis.

Measurement of tyrosine hydroxylase transcripts in bone marrow using biopsied tissue instead of aspirates for neuroblastoma

BACKGROUND

Molecular detection of tyrosine hydroxylase (TH) transcripts by quantitative RT-PCR (qRT-PCR) is a sensitive method to detect neuroblastoma (NB) cells in the bone marrow (BM). However, its clinical utility following chemotherapy has not been thoroughly investigated.

PROCEDURES

TH transcripts in the BM were measured by qRT-PCR both at diagnosis and during the course of chemotherapy. The results were analyzed with respect to assay timing, tumor volume and histological findings.

RESULTS

TH transcripts were detected in 100% of BM aspirates at diagnosis in cases with concurrent tumor involvement in the BM section; however, the proportion of TH transcript positive BM aspirates in cases with concurrent tumor involvement in the BM section gradually decreased following chemotherapy (55.5% after three cycles, 28.6% after six cycles and 0% after nine or more cycles of chemotherapy). Decreased proportion of TH transcript positive BM aspirates was associated with reduced tumor volume in the BM and differentiation of tumors into mature forms during chemotherapy. When qRT-PCR was performed with both aspirated and biopsied tissue during chemotherapy, TH transcripts were detected in BM tissue not only in all of the histology-positive cases but also in some of the histology-negative cases, while the proportion of TH transcript positive BM aspirates was low, even in histology-positive cases.

CONCLUSIONS

Measurement of TH transcripts in BM aspirates does not appear to be clinically useful during or after chemotherapy. Therefore, molecular monitoring of NB cells during or after chemotherapy using BM tissue is more optimal than testing on BM aspirates.

Consensus criteria for sensitive detection of minimal neuroblastoma cells in bone marrow, blood and stem cell preparations by immunocytology and QRT-PCR: recommendations by the International Neuroblastoma Risk Group Task Force

Disseminating disease is a predictive and prognostic indicator of poor outcome in children with neuroblastoma. Its accurate and sensitive assessment can facilitate optimal treatment decisions. The International Neuroblastoma Risk Group (INRG) Task Force has defined standardised methods for the determination of minimal disease (MD) by immunocytology (IC) and quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) using disialoganglioside G(D2) and tyrosine hydroxylase mRNA respectively. The INRG standard operating procedures (SOPs) define methods for collecting, processing and evaluating bone marrow (BM), peripheral blood (PB) and peripheral blood stem cell harvest by IC and QRT-PCR. Sampling PB and BM is recommended at diagnosis, before and after myeloablative therapy and at the end of treatment. Peripheral blood stem cell products should be analysed at the time of harvest. Performing MD detection according to INRG SOPs will enable laboratories throughout the world to compare their results and thus facilitate quality-controlled multi-centre prospective trials to assess the clinical significance of MD and minimal residual disease in heterogeneous patient groups.

Immunologic and therapeutic synergy of IL-27 and IL-2: enhancement of T cell sensitization, tumor-specific CTL reactivity and complete regression of disseminated neuroblastoma metastases in the liver and bone marrow

IL-27 exerts antitumor activity in murine orthotopic neuroblastoma, but only partial antitumor effect in disseminated disease. This study demonstrates that combined treatment with IL-2 and IL-27 induces potent antitumor activity in disseminated neuroblastoma metastasis. Complete durable tumor regression was achieved in 90% of mice bearing metastatic TBJ-IL-27 tumors treated with IL-2 compared with only 40% of mice bearing TBJ-IL-27 tumors alone and 0% of mice bearing TBJ-FLAG tumors with or without IL-2 treatment. Comparable antitumor effects were achieved by IL-27 protein produced upon hydrodynamic IL-27 plasmid DNA delivery when combined with IL-2. Although delivery of IL-27 alone, or in combination with IL-2, mediated pronounced regression of neuroblastoma metastases in the liver, combined delivery of IL-27 and IL-2 was far more effective than IL-27 alone against bone marrow metastases. Combined exposure to IL-27 produced by tumor and IL-2 synergistically enhances the generation of tumor-specific CTL reactivity. Potentiation of CTL reactivity by IL-27 occurs via mechanisms that appear to be engaged during both the initial sensitization and effector phase. Potent immunologic memory responses are generated in mice cured of their disseminated disease by combined delivery of IL-27 and IL-2, and depletion of CD8(+) ablates the antitumor efficacy of this combination. Moreover, IL-27 delivery can inhibit the expansion of CD4(+)CD25(+)Foxp3(+) regulatory and IL-17-expressing CD4(+) cells that are otherwise observed among tumor-infiltrating lymphocytes from mice treated with IL-2. These studies demonstrate that IL-27 and IL-2 synergistically induce complete tumor regression and long-term survival in mice bearing widely metastatic neuroblastoma tumors.

Minimal disease monitoring by QRT-PCR: guidelines for identification and systematic validation of molecular markers prior to evaluation in prospective clinical trials

Real-time RT-PCR (QRT-PCR) is a sensitive method for the detection of minimal disease (MD) and may improve monitoring of disease status and stratification of patients for therapy. Where tumour-specific mRNAs have not been identified, the selection of which target(s) is(are) optimal for the detection of MD remains a challenge. This reflects the heterogeneity of tumour cells, the stability of mRNAs and low-level of transcription in cells of the normal haemopoietic compartments. The aim of this study was to establish for the first time guidelines for the systematic prioritization of potential markers of MD detected by QRT-PCR prior to evaluation in multicentre prospective clinical outcome studies. We combined microarray analysis, ESTs gene expression profiles, improved probe-sets sequence annotation, and previously described standard operating procedures for QRT-PCR analysis to identify and prioritize potential markers of MD. Using this methodology, we identified 49 potential markers of MD in neuroblastoma (NB), of which 11 were associated with neuronal function. We found that, in addition to TH, Phox2B and DCX mRNA may be useful targets for the detection of MD in children with NB. This same strategy could be exploited to select MD markers of other solid tumours from the large number of potential targets identified by microarray gene expression profiles.

Standardisation of operating procedures for the detection of minimal disease by QRT-PCR in children with neuroblastoma: Quality assurance on behalf of SIOPEN-R-NET

The clinical utility of detecting minimal residual disease (MRD) in children with neuroblastoma (NB) by quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) is not clear. This in part reflects the lack of uniform methodology for analysis and reporting. Reference laboratories across Europe have therefore established standard operating procedures (SOPs) for the detection of NB cells by QRT-PCR. Haemopoietic samples are collected into PAXgene blood RNA tubes, which stabilise mRNA for 48 h at room temperature and more than 6 months at -80 degrees C. Tyrosine hydroxylase (TH) was selected as the target for NB cell detection, expression is normalised to beta2-microglobulin and reported using the DeltaDeltaCt method. The sensitivity of QRT-PCR increased from 58% to 90% following the development of SOPs. A robust, transferable, objective method for the detection of NB cells by QRT-PCR has been defined to improve the power and consistency of studies on MRD in children with NB.

Pilot study to evaluate MYCN expression as a neuroblastoma cell marker to detect minimal residual disease by RT-PCR

This pilot study was performed to determine whether MYCN expression warrants further investigation as a tumor marker to detect low levels of residual neuroblastoma (NB). Seven NB cell lines and 30 bone marrow (BM) samples from patients with high-risk NB were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) for MYCN expression, and for the established NB marker tyrosine hydroxylase. MYCN was expressed in all 7 NB cell lines, but not in normal peripheral blood, CD34 cells, or BM. In dilution studies using cell lines with or without DNA amplification of MYCN, 1 NB cell in 10 to 10 nucleated blood cells was detectable by RT-PCR. MYCN was identified in all 21 BM samples in which tumor cells were identified by histologic examination, including 4 samples in which tyrosine hydroxylase was not detected. Additionally, expression of both markers was detected in 5 samples that were negative by histology but presumably contained low levels of tumor cells, consistent with the greater sensitivity of RT-PCR compared with morphologic methods. Detection of MYCN RNA was independent of MYCN DNA amplification status. The selective expression of MYCN in tumor cells, and the sensitivity of detection of MYCN by RT-PCR noted in this and other studies, supports further evaluation of MYCN as a NB marker for molecular detection of minimal residual disease.

Detecting minimal residual disease in neuroblastoma patients-the present state of the art

While cyto- and histological screening of bone marrow samples are still accepted as the gold standard for initial staging of neuroblastoma patients, these applications are insufficient during or after therapy because it is not always possible to detect tumour cell infiltration below the level of 1% by morphology alone. For monitoring of minimal residual disease, techniques offering a considerably higher sensitivity have been developed. Immunocytology, RT-PCR and flow cytometry are most frequently used, but differ with regard to targets (single cells, RNA transcripts), measured parameters (tumour cell number, antigen expression, cytomorphology, cytogenetic aberrations, level/number of RNA transcripts), specificity (uni-/multi-parameter analysis) and sensitivity (number of investigated cells). The pros and cons of these methods are reviewed. Precise quantification of residual tumour cells in bone marrow and blood may show a future impact on risk grouping and therapeutic strategies for patients with disseminated disease, but the potential clinical application of these techniques has to be preceded by thorough standardisation and validation in multi-centre studies.

Standardization of the immunocytochemical detection of neuroblastoma cells in bone marrow

Standard cytomorphological examination of bone marrow (BM) aspirates does not appear to be sensitive enough to detect single neuroblastoma cells. The SIOPEN Neuroblastoma Bone Marrow Committee developed a sensitive and reproducible anti-GD2 immunocytochemical assay and introduced morphological and immunocytological criteria for the interpretation of results. Fixed cytospins were incubated with a commercially available anti-GD2 monoclonal antibody and an APAAP kit. Cells fulfilling all morphological and immunocytological criteria were called criteria-positive cells (CPCs). Not convincingly interpretable cells fulfilled some, but not all, criteria, and negative cells displayed only exclusion criteria. The genetic profile of doubtful cells was checked by fluorescence in situ hybridization. Ideally, 3 x 10(6) cells were analyzed to reach a 95% probability of detecting one tumor cell in 1 x 10(6) mononuclear cells. Four quality control rounds were organized to validate the method. A total of 111 quality control samples were analyzed. Two main improvements were achieved: in discordant cases, the range between the lowest and highest reported result was reduced by half, and discordant results were only found in samples with less than 10 CPCs per 1 x 10(6). This article describes the first internationally standardized protocol to detect and quantify rare neuroblastoma cells by immunocytochemistry. This method is an indispensable tool for multicenter studies evaluating the clinical significance of minimal residual disease in neuroblastoma.

The Doublecortin Gene, A New Molecular Marker to Detect Minimal Residual Disease in Neuroblastoma

Neuroblastoma (NB) is a pediatric cancer of highly variable clinical outcome. Much effort is devoted to detection of minimal residual (MRD) disease through RT-PCR or immunology of tissue-specific markers. Tyrosine hyrdroxylase (TH) has demonstrated a high utility to assess disease dissemination, although this marker can be lost due to clonal variability. Here we propose the use of the doublecortin (DCX) gene as a new molecular marker of neuroblastoma cells. DCX specifically appears in migrating neurons of the central and peripheral nervous system and interacts with and regulates the microtobule cytoskeleton. We have studied this gene by real-time quantitative RT-PCR in a total of 47 primary tumors and 202 samples of bone marrow or peripheral blood from 34 high-risk neuroblastoma patients as well as in 41 normal controls. The expression of DCX demonstrated a good specificity and concordance with TH, showing a higher expression rate in all the sample types studied as well as at different time points from diagnosis. We conclude that DCX would be a more efficient marker of minimal disease in neuroblastoma and perhaps other tumors of neuronal lineage.

Measuring circulating neuroblastoma cells by quantitative reverse transcriptase-polymerase chain reaction analysis

BACKGROUND

Histologic examination of bone marrow (BM) is an accepted clinical standard for the detection of metastatic neuroblastoma (NB). Circulating tumor cells in peripheral blood (PB) derive from depots other than BM, and its measurement may provide additional information in the management of patients with NB.

METHODS

One hundred twenty patients with Stage 4 NB were evaluated for tumor cell content in PB by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis of GD2 synthase mRNA with a sensitivity of 1 NB cell in 10(6) normal cells. These findings were correlated with qRT-PCR analysis of their simultaneously sampled BM aspirates and 5 standard modalities of disease detection (histology, computed tomography/magnetic resonance imaging, bone scan, metaiodobenzylguanidine scan, and urinary homovanillic acid/vanillylmandelic acid levels).

RESULTS

Detection of GD2 synthase transcript was found in 62 patients: Eleven patients had positive (+) samples in their BM and PB (BM+PB+), 38 patients had BM+PB-negative (BM+PB-) specimens, and 13 patients had BM-PB+ samples. BM+PB+ paired samples had the highest transcript levels. When the extent of disease was scored (from 0 to 5) according to the number of positive disease detection modalities, the magnitude of the transcript level correlated with disease score. Ninety-one percent of patients with BM+PB+ samples had evidence of disease in >/= 3 modalities, whereas 97% of patients with BM-PB- samples and 100% of patients with BM-PB+ samples had low disease scores </= 2. Marker positivity in BM correlated with disease score. Patients who had positive marker in BM or PB had higher rates of relapse and death compared with patients who had negative marker. Kaplan-Meier analysis demonstrated a significantly greater risk of death for patients who had BM+PB+ specimens compared with patients who had BM-PB- samples (P = 0.03).

CONCLUSIONS

BM monitoring should continue to be an integral part of disease follow-up for patients with Stage 4 NB. PB monitoring to complement tumor surveillance in the BM can be informative.

Molecular Detection of Dopamine Decarboxylase Expression by Means of Reverse Transcriptase and Polymerase Chain Reaction in Bone Marrow and Peripheral Blood

A highly sensitive molecular method was used to evaluate the presence of dopamine decarboxylase (DDC) mRNA in the bone marrow and peripheral blood of patients with neuroblastoma (NB). DDC, like tyrosine hydroxylase (TH), is an enzyme involved in the catecholamine synthesis pathway and has recently been proposed as a specific marker of NB among pediatric malignancies. DDC transcript was detected in five of five NB cell lines, 10 of 10 NB primary tumors, 17 of 18 (94%) bone marrow samples, and 12 of 18 (66%) blood samples drawn at diagnosis in 18 patients affected by disseminated NB. In contrast, no PCR signal was found in 20 bone marrow samples obtained from patients with other malignancies or in eight of nine marrow and blood samples drawn from patients with localized NB (two stage 2 and seven stage 3). In addition, all marrow and blood samples obtained from NB patients at relapse revealed DDC mRNA. Furthermore, the percentage of DDC-positive samples was lower among the samples drawn from these patients during treatment. By comparison with conventional methods for disease evaluation, DDC transcript research can increase the sensitivity of NB cell detection in marrow and blood samples at diagnosis and during the treatment and follow-up of NB patients. These results suggest that finding DDC mRNA in NB patients could be a potential marker for minimal residual disease study.

Comparison of two methods for evaluating bone marrow metastasis of neuroblastoma: Reverse transcription-polymerase chain reaction for tyrosine hydroxylase and magnetic resonance imaging

BACKGROUND

The presence of bone marrow (BM) metastasis and circulating tumor cells in patients with neuroblastoma is a significant prognostic factor at diagnosis and might antedate detection of a relapse by other diagnostic studies. In this study, the clinical value of reverse transcription-polymerase chain reaction (RT-PCR) to amplify mRNA for tyrosine hydroxylase (TH) and magnetic resonance imaging (MRI) during the clinical course of patients with advanced neuroblastoma, was evaluated.

METHODS

Four patients with Stage 1, 4 or 4S neuroblastoma, were studied. BM and peripheral blood (PB), including peripheral blood stem cell (PBSC), samples were examined for TH mRNA using RT-PCR. Concurrently, MRI detection of BM metastasis was used.

RESULTS

In all cases, except one that had no evidence of BM invasion, TH mRNA in BM and PB at diagnosis were positive, and TH mRNA at diagnosis disappeared after chemotherapy. In two cases, although involvement in the neurocentrum BM was detected by MRI, TH mRNA in the iliac crest BM was negative. The pathological area still remained on MRI after intensive therapy.

CONCLUSION

RT-PCR for TH mRNA might be the most sensitive method for the detection of occult neuroblastoma cells in BM and PB. However, because invasion of the BM by neuroblastoma may have a focal distribution, sampling errors can occur. Therefore, not only RT-PCR but also MRI, need to be used to rule out marrow involvement, especially at diagnosis and BM relapse.

Micrometastases in neuroblastoma: are they clinically important?

Despite advances in the treatment of neuroblastoma (NBL), recurrence and metastases continue to pose major problems in clinical management. The relation between micrometastases and the development of secondary disease is not fully understood. However, accurate methods to detect low numbers of tumour cells may allow the evaluation of their role in the disease process, and by implication the possible benefits of eliminating them. Although there is substantial evidence for the increased sensitivity of current molecular methods for the detection of NBL cells compared with more conventional cytology, the clinical relevance and usefulness of detecting this disease remain controversial. The primary goal of current translational research must be to evaluate the clinical relevance of micrometastatic disease detected by these methods in multicentre prospective clinical outcome studies. Only then can the clinical usefulness of these methods be defined so that they may be introduced into relevant clinical practice.

Detection of disseminated tumor cells in neuroblastoma: 3 log improvement in sensitivity by automatic immunofluorescence plus FISH (AIPF) analysis compared with classical bone marrow cytology

The sensitive detection of bone marrow involvement is crucial for tumor staging at diagnosis and for monitoring of the therapeutic response in the patient's follow-up. In neuroblastoma, only conventional cytomorphological techniques are presently accepted for the detection of bone marrow involvement, yet since the therapeutic consequences of the bone marrow findings may be far-reaching, the need for highly reliable detection methods has become evident. For this purpose, we developed an automatic immunofluorescence plus FISH (AIPF) device which allows the exact quantification of disseminated tumor cells and the genetic verification in critical cases. In this study, the power of the immunofluorescence technique is compared with conventional cytomorphology. 198 samples from 23 neuroblastoma patients (stages 4 and 4s) at diagnosis and during follow-up were investigated. At diagnosis, 45.6% of the samples (26 of 57) which were positive by AIPF investigation were negative by cytomorphology. During follow-up, 74.2% (49 of 66) of AIPF-positive samples showed no cytological signs of tumor cell involvement. False negative morphological results were found in up to 10% of tumor cell content. A tumor cell infiltrate below 0.1% was virtually not detectable by conventional cytomorphology. Using the sensitive immunofluorescence technique, the analysis of only two instead of four puncture sites did not lead to false negative results. Thus, the immunofluorescence technique offers an excellent tool for reliable detection and quantification of disseminated tumor cells at diagnosis and during the course of the disease.

Myogenin--a more specific target for RT-PCR detection of rhabdomyosarcoma than MyoD1

BACKGROUND

MyoD1 and myogenin are differentially expressed in early myogenesis and have been identified in rhabdomyosarcoma (RMS). This study evaluates reverse transcriptase-polymerase chain reaction (RT-PCR) for MyoD1 and myogenin mRNA as diagnostic markers of RMS, and the potential application of this method for the detection of small volume disease in bone marrow (BM) and peripheral blood (PB).

PROCEDURE

Expression of MyoD1 and myogenin mRNA was examined by RT-PCR in RMSs (9 alveolar RMS, 10 embryonal RMS, 1 pleomorphic RMS), and 21 other paediatric tumor samples (10 neuroblastoma, 10 Ewing sarcomas, and 1 Sarcoma (not otherwise specified) (S(NOS)). BM (n = 19) and PB (n = 22) samples from the same RMS study population were also examined for MyoD1 and myogenin mRNA expression.

RESULTS

Positive expression of both markers was demonstrated in adult muscle, but not in normal PB. Myogenin mRNA was expressed in 16/18 and MyoD1 mRNA in 12/12 RMSs studied. Myogenin was not expressed in 10/10 neuroblastomas, but was present in 2/10 Ewing sarcomas. However, MyoD1 mRNA was detected in 10/10 Ewing sarcomas and 7/10 neuroblastomas. Myogenin mRNA was detected in two BM samples from children with histologically negative BM and in 1/22 PB samples. Detection of MyoD1 mRNA in BM and PB was compromised by the amplification of a similar sized, non-specific product.

CONCLUSIONS

Myogenin mRNA is a more specific marker than MyoD1 for the diagnosis of RMS. Myogenin mRNA is potentially a useful target for the assessment of small volume disease in RMS.

Detection procedures for neuroblastoma cells metastatic to blood and bone marrow: blinded comparison of chromogranin A heminested reverse transcription polymerase chain reaction to tyrosine hydroxylase nested reverse transcription polymerase chain reaction and to anti-GD2 immunocytology

Specific and sensitive tumor cell detection is becoming increasingly important for diagnosing and staging as well as for the therapeutic management of neuroblastoma patients. We propose a chromogranin A heminested reverse transcription polymerase chain reaction (CgA hn RT-PCR) procedure for the detection of neuroblastoma minimal residual disease in peripheral blood and bone marrow samples. The results were checked in comparison with the presently available procedures (i.e., with the tyrosine hydroxylase nested RT-PCR [TH n RT-PCR] and with the immunocytochemical approach using anti-GD2 antibodies). Controls from healthy patients or from people with unrelated disease (12 samples of bone marrow and 23 samples of peripheral blood) and serial dilution experiments using neuroblastoma cell lines (SKNLP, SKNFI, STA6, STA8) showed CgA hn RT-PCR full specificity and sensitivity ranging from 10(3) to 10(6) (depending on the cell line). The results compared favorably with those obtained using TH n RT-PCR. Preliminary data obtained analyzing bone marrow and peripheral blood specimens from stage IV neuroblastomas showed substantially overlapping results between CgA and TH n RT-PCR procedures. Our data support the potential usefulness of CgA heminested RT-PCR as a specific and sensitive procedure for minimal disease detection in neuroblastoma. A prospective evaluation of this tool in clinical studies might be warranted.

Circulating neuroblastoma cells detected by reverse transcriptase polymerase chain reaction for tyrosine hydroxylase mRNA are an independent poor prognostic indicator in stage 4 neuroblastoma in children over 1 year

PURPOSE

In this prospective, multicenter study, the independent prognostic power of neuroblastoma cells detected by reverse transcriptase polymerase chain reaction (RT-PCR) for tyrosine hydroxylase (TH) mRNA was evaluated.

PATIENTS AND METHODS

The clinical significance of disease detected by RT-PCR in peripheral blood from children at diagnosis was compared with established prognostic markers [ie, age, lactate dehydrogenase (LDH), neuron-specific enolase, ferritin, and MYCN gene amplification] by multivariate analysis. The value of disease detection by RT-PCR during treatment and follow-up was also examined.

RESULTS

TH mRNA was detected in peripheral blood from 33 of 49 (67%) children with stage 4 neuroblastoma > 1 year old at diagnosis and was a significant predictive factor for overall survival [hazard ratio (HR) = 2.40, 95% confidence interval (CI) 1.19 to 4.84, P =.014) and event-free survival (HR = 2.09, 95% CI 1.06 to 4.17, P =.034) in a multivariate analysis. Detection of disease in blood from clinically disease-free children was related to increased risk of death (HR 2.54, 95% CI 1.42 to 4.55, P =.0014).

CONCLUSION

TH mRNA in peripheral blood of children with neuroblastoma is a poor prognostic indicator, reflecting the propensity for dissemination via the bloodstream. When combined with a serum LDH > 1500 IU/L, this is the most powerful poor prognostic model at diagnosis for children > 1 year old with stage 4 disease. The detection of TH mRNA in peripheral blood from clinically disease-free children is related to increased risk of relapse and death.

Quantitative tumor cell content of bone marrow and blood as a predictor of outcome in stage IV neuroblastoma: a Children's Cancer Group Study

PURPOSE

This study investigated the prognostic value of quantifying tumor cells in bone marrow and blood by immunocytology in children with high-risk, metastatic neuroblastoma.

PATIENTS AND METHODS

Patients with stage IV neuroblastoma (N = 466) registered on Children's Cancer Group study 3891 received five cycles of induction chemotherapy and were randomized either to myeloablative chemoradiotherapy with autologous purged bone marrow rescue or to nonmyeloablative chemotherapy. Subsequently, they were randomized to 13-cis-retinoic acid or no further treatment. Immunocytologic analyses of bone marrow and blood were performed at diagnosis, week 4, week 12, bone marrow collection, and end induction and were correlated with tumor biology, clinical variables, treatment regimen, and event-free survival (EFS).

RESULTS

Immunocytology identified neuroblastoma cells in bone marrow of 81% at diagnosis, 55% at 4 weeks, 27% at 12 weeks, 19% at bone marrow collection, and 14% at end induction. Tumor cells were detected in blood of 58% at diagnosis and 5% at collection. There was an adverse effect on EFS of increasing tumor cell concentration in bone marrow at diagnosis (P =.04), at 12 weeks (P =.006), at bone marrow collection (P <.001), and at end induction (P =.07). Positive blood immunocytology at diagnosis was associated with decreased EFS (P: =.003). The prognostic impact of immunocytology was independent of morphologically detected bone marrow disease, MYCN status, and serum ferritin level in bivariate Cox analyses.

CONCLUSION

Immunocytologic quantification of neuroblastoma cells in bone marrow and blood at diagnosis and in bone marrow during induction chemotherapy provides prognostic information that can identify patients with very high-risk disease who should be considered for experimental therapy that might improve outcome.

Clinical implications of minimal disease in the bone marrow and peripheral blood in neuroblastoma

PURPOSE

In patients with neuroblastoma (NB), minimal disease (MD) in bone marrow (BM) and peripheral blood (PB) is thought to play an important role in metastasis. The current study was designed to evaluate the clinical implications of the detection of MD in NB at the initial diagnosis.

METHODS

Expression of the neuroendocrine protein gene product 9.5 (PGP9.5) and tyrosine hydroxylase (TH) mRNA in BM and PB obtained from 18 patients with NB was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

MD was detected in the BM obtained from 4 of 14 localized NB patients and also in the PB from 2. However, it was found also in both the BM and PB obtained from all 4 patients with metastatic NB. Two of the 4 MD-positive patients with localized NB had metastatic recurrence after a complete tumor excision. They also had unfavorable biological prognostic factors compared with the other 2 who did not have recurrent disease.

CONCLUSION

MD detected by RT-PCR in the BM and the PB of patients with NB thus suggests a risk for metastatic disease, which in association with other unfavorable biological features may indicate a poor prognosis.

Long-term results of CD34(+) cell transplantation in children with neuroblastoma

BACKGROUND

This is the first report of the long-term results of CD34(+) cell transplantation in children with neuroblastoma. We investigated the hematologic and immune recovery, posttransplant morbidity, and clinical outcome of these children.

PROCEDURE

Twenty-three children with advanced neuroblastoma had PBPCs (20 patients) or BM (3 patients) collected, followed by CD34(+) cell selection on Ceprate column. The purge of residual neuroblastoma cells was evaluated using an RT-PCR for tyrosine hydroxylase (TH) mRNA assay. Reinfusion of CD34(+) cells followed busulfan + melphalan myeloablative chemotherapy.

RESULTS

A median of 2.9 x 10(6) CD34(+) cells/kg was reinjected. Median days to achieve ANC > 0.5 x 10(9)/liter and platelets > 50 x 10(9)/liter were 13 (range 9-33) and 59 (range 22-259), respectively. Circulating T cells were primarily CD4(-)/CD8(+) with fewer than 0.2 10(9)CD4(+) cells/liter throughout the first 6 months. CD19(+) cells and CD56(+) cells were not detectable up to day +35 posttransplant. At 1 year posttransplant, 16 evaluable patients had stable hematopoiesis with 2.3 x 10(9) ANC/liter (range 0.8-4.1), 1.4 x 10(9) lymphocytes/liter (range 0.5- 2.0) and 251 x 10(9) PLT/liter (range 35-490). After the completion of hematopoietic reconstitution, six events of severe septicemia/septic shock were noted. Six children had severe VZV infections, and 2 had EBV-associated lymphoproliferation. Thirteen patients are alive with a median follow-up of 40 months (range 2-54). Ten patients have died; 8 relapsed or developed progressive disease, 1 died from nondocumented pneumopathy at day 56, and 1 developed AML-M4 at 3 years posttransplant.

CONCLUSIONS

In children, CD34(+) cell transplantation can be accomplished with a reduction of neuroblastoma cell inoculum in the selected graft as assessed by RT-PCR analysis. CD34(+) cell grafts provide successful neutrophil reconstitution. However, delayed platelet recovery, persistent decrease in CD4(+) lymphocyte levels and a high incidence of serious and life-threatening late infections were observed in these children. There remains a critical need to evaluate any real clinical benefit of CD34(+) cell autografts in neuroblastoma patients.

Molecular detection of cancer cells in bone marrow and peripheral blood of patients with operable breast cancer. Comparison of CK19, MUC1 and CEA using RT-PCR

We have compared three different RT-PCR procedures to measure cytokeratin 19 (CK19), carcinoembryonic antigen (CEA) and mucin MUC1 gene expression in order to determine their diagnostic value in detecting tumour cells in bone marrow aspirates of patients with operable breast cancer. In an experimental model, the best sensitivity was observed for CK19 and MUC1 RT-PCR assays, although only the CEA and CK19 assays showed good specificity. The study of 42 patients showed that a 'CK19 positive/CEA positive' RT-PCR assay in bone marrow correlated positively with a positive axillary lymph node status (N(0) versus N(1-3), P<0.05). Both assays were also positive in 17% of node negative patients. RT-PCR assays were more sensitive in bone marrow than in peripheral blood. Our results suggest that CK19 and CEA RT-PCR assays are powerful methods for detecting disseminated breast cancer cells. A larger study with long-term follow-up is required in order to clarify their clinical usefulness.

Molecular detection of low-level disease in patients with cancer

The accurate detection of low-level disease in patients with cancer is essential to improve the staging of disease and consequently to define appropriate treatment strategies. Most methods currently used for staging are based on imaging studies and histological and immunocytochemical analysis of tissues such as bone marrow aspirates, or antibody assays for marker proteins secreted into the circulation. These methods have limited sensitivity. However, assays for nucleic acid-based markers may be valuable tools for the sensitive detection, assessment, and monitoring of disease status in asymptomatic cancer patients. Application of these methods may allow the early detection of cancer, when the tumour burden is smaller and the disease potentially more curable. The last decade has seen the application of polymerase chain reaction (PCR)-based methods to the detection of tumour in a wide variety of compartments, including peripheral blood, bone marrow, lymph nodes, urine, sputum, faeces, pancreatic juice, and more recently plasma. Molecular detection of disease by PCR has targeted DNA and RNA markers, including mutations, microsatellites, and tissue-specific gene expression. It is likely that these molecular methods will provide important clinical information, though their current clinical utility remains unclear. The current status of nucleic acid-based assays for the detection and assessment of disease status in the management of patients with solid tumours is reviewed.

Use of tumor-specific gene expression for the differential diagnosis of neuroblastoma from other pediatric small round-cell malignancies

The differential diagnosis of neuroblastoma from other small round-cell tumors of childhood, although clinically of great importance, is sometimes difficult due to the almost indistinguishable appearance of such tumors by conventional microscopy. Because neuroblastomas are characterized by the synthesis of catecholamines, we investigated the possibility that expression of genes involved in this pathway could serve as a molecular marker for this disease. A reverse transcriptase polymerase chain reaction assay was used to analyze expression of tyrosine hydroxylase and dopa decarboxylase in 84 pediatric malignancies including 55 neuroblastomas, 6 Ewing's sarcomas/primitive neuroectodermal tumors, 7 lymphomas, 6 leukemias, 2 rhabdomyosarcomas, 6 osteosarcomas, and 2 phaeochromocytomas. Of the 55 neuroblastoma samples analyzed, 54 expressed clearly detectable levels of both genes. The one sample that did not express either of the genes was rediagnosed both clinically and by molecular genetic analysis as a Ewing's sarcoma. Of the 29 non-neuroblastoma tumor samples examined, the only tumor samples that expressed clearly detectable levels of both tyrosine hydroxylase and dopa decarboxylase were phaeochromocytomas. Like neuroblastomas, these tumors are characterized by high levels of catecholamines. These findings suggest that expression of genes involved in catecholamine biosynthesis may be useful for differentiating neuroblastoma from other small round-cell tumors of childhood.

Haematogenous cytokeratin 20 mRNA as a predictive marker for recurrence in oral cancer patients

We examined the expression of cytokeratin 20 (CK20) mRNA in the peripheral blood of oral squamous cell carcinoma (SCC) patients by reverse transcriptase polymerase chain reaction (RT-PCR). Eleven out of 12 oral SCC patients showed positive RT-PCR results. However, there is no clear relationship between the haematogenous CK20 mRNA and the metastasis. After initial treatment, all of the tumour-free survivors tested showed negative RT-PCR results. CK20 mRNA in peripheral blood can be used as a marker for tumour recurrence but not not for metastasis in oral SCC patients.

Improved methods using the reverse transcriptase polymerase chain reaction to detect tumour cells

Reverse transcriptase polymerase chain reaction (RT-PCR) is increasingly used to detect small numbers of circulating tumour cells, though the clinical benefit remains controversial. The largest single contributing factor to the controversy of its value is the different approaches to sample processing. The aim of this study was to compare the sensitivity and reproducibility of RT-PCR for the detection of tumour cells after four commonly used different methods of sample processing. Using RT-PCR, one tumour cell spiked in 2 ml of whole blood was detected after analysis of separated mononuclear cell RNA, whole blood total or poly-A+ RNA. No false positives were identified with any method. However, the reproducibility of tumour cell detection was reduced after isolation of the mononuclear cell fraction. Only analysis of poly-A+ RNA had a sensitivity of 100% in all the cell spiking experiments. In patient blood samples, analysis of poly-A+ RNA increased the number of blood samples positive for tyrosine hydroxylase (TH) mRNA compared with those positive after analysis of total RNA. This may reflect high levels of cDNA reducing the efficiency of the PCR. Isolation of poly-A+ RNA increases the sensitivity and reproducibility of tumour cell detection in peripheral blood.

Targeted interleukin-2 therapy for spontaneous neuroblastoma metastases to bone marrow

BACKGROUND

Advanced (stage 4) cases of neuroblastoma, a childhood cancer of the nervous system, are associated with high relapse rates, even after intensive chemotherapy, radiotherapy, and autologous bone marrow transplantation. Therefore, the use of monoclonal antibodies directed against the neuroblastoma tumor marker disialoganglioside GD2 (GD2), in combination with recombinant human interleukin 2 (rhIL-2), is under clinical investigation. We hypothesize that targeted cytokine immunotherapy with a recombinant anti-GD2 antibody-interleukin 2 fusion protein (ch14.18-IL-2) is superior to a combination of ch14.18 and rhIL-2. Our purpose was as follows: 1) to develop a syngeneic model for murine neuroblastoma that expresses GD2 and features both experimental and spontaneous metastases to bone marrow and liver, and 2) to assess anti-GD2-targeted IL-2 therapy in this mode.

METHODS

A hybrid neuroblastoma cell line was used to generate the GD2-positive NXS2 cell line. Bone marrow and liver metastases were quantified by reverse transcription-polymerase chain reaction for tyrosine hydroxylase and by organ weight or counts of macroscopic tumor foci, respectively. All P values reported are two-sided.

RESULTS

Injection of NXS2 cells resulted in disseminated bone marrow and liver metastases exhibiting stable, but heterogeneous expression of GD2. Treatment with fusion protein (10 microg/day for 6 days) effectively suppressed growth of both experimental and spontaneous metastases to bone marrow and liver (P<.001). In contrast, a mixture of rhIL-2 and ch14.18 at equivalent dose levels was inefficient. Only mice treated with ch14.18-IL-2 showed a twofold prolongation in life span (P<.001).

CONCLUSION

Targeted IL-2 therapy with a ch14.18-IL-2 fusion protein elicits an effective antitumor response. Our data suggest that a study of ch14.18-IL-2 as an adjuvant treatment in patients with minimal residual disease may be of value.

Low specificity of PGP9.5 expression for detection of micrometastatic neuroblastoma

To determine the specificity of neuroendocrine protein gene product (PGP9.5) gene transcripts for detecting micrometastatic neuroblastoma, we have used a highly sensitive polymerase chain reaction (PCR) technique to evaluate expression of this gene in normal blood and bone marrow. While expression of the tyrosine hydroxylase gene was not detected in any normal sample, low-level PGP9.5 expression was detected in eight out of ten blood and seven of 12 marrow samples. PGP9.5 gene transcripts in normal tissues have the potential to interfere with the detection of micrometastatic neuroblastoma.

Clinical application of minimal residual neuroblastoma cell detection by reverse transcriptase-polymerase chain reaction

The highly sensitive method to detect neuroblastoma (NB) cells using reverse transcriptase polymerase chain reaction (RT-PCR) was applied in the practical clinics, and its efficacy was assessed in the present study. Human tyrosine hydroxylase (TH), a rate-limiting enzyme in the catecholamine biosynthesis, was used as the marker for NB cells, and the expression of THmRNA was examined in 13 samples (four peripheral blood and nine bone marrow) harvested from seven patients (four with stage IV, one with stage III, two with stage II) using RT-PCR with our original primers. The positive signals for NB cells were detected in four samples (one peripheral blood and three bone marrow) by the PCR method, but were undetectable by the conventional histological examinations. In the present series, a case that showed a positive signal for NB cells in the peripheral blood showed a remarkably unfavorable clinical course, indicating that the circulating NB cells detected by the PCR method can be a sign of the progressively advanced NB, and may define a new prognostic factor suggesting higher risk. In another case, the PCR detection for the residual NB cells in the bone marrow provided important supporting evidence to determine the necessity of the additional chemotherapy and the suitable timing for bone marrow transplantation. This detection also guaranteed the safety of the bone marrow for transplantation. The PCR method was considered to be very beneficial in the selected cases. However, some problems such as the false-negative results in the negative urinary vanillylmandelic acid secretor were also highlighted in the present study.

Reverse transcriptase-polymerase chain reaction for expression of tyrosinase to identify malignant melanoma cells in peripheral blood

BACKGROUND

Circulating tumour cells in the peripheral blood may be important for haematogenous spread of disease. The detection of these cells may therefore be a poor prognostic indicator. Reverse-transcriptase polymerase chain reaction (RT-PCR) of target tumour-specific protein expression has been used as a sensitive and specific method for the detection of these tumour cells. Initial reports by our laboratory and other suggested RT-PCR amplification of the enzyme tyrosinase is a useful method for detection of melanoma cells in peripheral blood [1-3].

PATIENTS AND METHODS

In this report, we have evaluated the application of RT-PCR for tyrosinase mRNA as a detection method for melanoma cells in a series of 24 patients with advanced, metastatic malignant melanoma. A single round RT-PCR method is described.

RESULTS

The single round RT-PCR was as sensitive as previously described nested PCR methods, and had the advantage of reduced contamination risks. Blood samples from three out of the twenty-four patients were positive.

CONCLUSIONS

The frequency of tumour cell detection in peripheral blood from patients with advanced disease was lower than previously reported. It may be only small numbers of circulating tumour cells are present at any one time in the peripheral blood of patients with malignant melanoma. If this is the case increased sampling will improve detection frequency. Alternatively, dissemination of melanoma through peripheral blood may be a rare event. In our experience, RT-PCR for tyrosinase mRNA as a staging test for melanoma patients must be interpreted cautiously.