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© 2000 American Society for Clinical Oncology Quantitative Tumor Cell Content of Bone Marrow and Blood as a Predictor of Outcome in Stage IV Neuroblastoma: A Childrens Cancer Group StudyFrom the Departments of Pediatrics and Pathology, University of Southern California School of Medicine and Childrens Hospital; and Department of Preventive Medicine, University of Southern California School of Medicine, Los Angeles; Childrens Cancer Group, Arcadia; and Department of Pediatrics, University of California School of Medicine, San Francisco, CA. Address reprint requests to Robert C. Seeger, MD, Childrens Cancer Group, PO Box 60012, Arcadia, CA 91066-6012; email rseeger{at}chla.usc.edu
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 Childrens 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.
BONE MARROW involvement by neuroblastoma is extremely common in children with metastatic disease, present by standard morphologic examination of aspirates and biopsies in 60% to 65% of children with stage IV disease at diagnosis.1 Detection of tumor by immunocytology, using a mixture of monoclonal antibodies reactive at the cell surface, has been shown to reliably detect tumor with a sensitivity that may vary from 1 to 10 in 105 nucleated bone marrow cells, depending on the method of detection.2-14 Detection of small numbers of contaminating tumor cells in bone marrow or blood may be a very important component of response evaluation and is critical for evaluation of hematopoietic stem cell products, because the use of myeloablative therapy followed by autologous bone marrow transplantation now has been shown in a randomized trial to be beneficial to event-free survival (EFS).15 The goal of this study was to determine whether quantitative sequential assessment of bone marrow and peripheral-blood tumor cells was prognostic for disease response at the end of induction therapy and for ultimate EFS. We report here the correlation of bone marrow and blood immunocytology with outcome for all assessable patients with metastatic neuroblastoma treated on Childrens Cancer Group (CCG) protocol CCG-3891.15 This protocol was a phase III study using a standard induction chemotherapy followed by randomization to myeloablative chemoradiotherapy with purged autologous bone marrow transplantation (ABMT) or to intensive nonmyeloablative consolidation chemotherapy, and a second randomization to no further treatment or 6 months of 13-cis-retinoic acid biotherapy.
Patients Eligible patients included newly diagnosed children (1 to 18 years of age) enrolled on the CCG-3891 protocol for high-risk neuroblastoma. Protocol eligibility included patients with the following clinical and biologic characteristics: age 1 year and Evans stage IV disease (n = 434); age less than 1 year with stage IV and tumor MYCN gene amplification (n = 19). Thirteen additional children who had localized disease treated with surgery alone at diagnosis but who then developed metastases and enrolled on CCG-3891 were also included. Other high-risk patients enrolled on the CCG-3891 study but who lacked metastases were excluded from the analyses reported in this article in order to examine only children with stage IV disease. Signed informed consent by parents or guardians was obtained, along with appropriate local institutional review board approval. Patient accrual began January 1991 and ended April 1996.
Serum ferritin was measured by radioimmunoassay: levels
Treatment
Bone Marrow and Blood Immunocytology, Bone Marrow Collection, and Purging Bone marrow was collected for ABMT and processed at the CCG Neuroblastoma Purging Center just before the fourth or fifth cycle of initial therapy if a diagnostic bone marrow aspirate obtained a week before collection had less than 1% tumor by morphologic and immunocytologic analysis. Bone marrow was purged using sedimentation, filtration, and two cycles of immunomagnetic separation.21-23 All infused marrows were tumor-free by bone marrow immunocytology.
Statistical Design and Analysis
Patients and Bone Marrow Immunocytology Samples A total of 466 children with stage IV or previously untreated low-stage disease that had metastasized were enrolled on CCG-3891. Of these patients, 422 had at least one bone marrow sample available for immunocytologic analysis. A total of 2,626 bone marrow immunocytology samples were obtained from these patients from diagnosis through the end of consolidation therapy. Only those obtained at diagnosis (n = 267), 4 weeks from diagnosis (n = 262), 12 weeks from diagnosis (after three cycles of induction chemotherapy; n = 244), 1 week before collection (n = 171), from the collected bone marrow (n = 200), and at the end of induction, approximately 20 to 24 weeks from diagnosis (n = 138), were included in the analyses here. Twenty-one patients had samples at six time-points, 62 patients had samples at five time-points, 92 patients had samples at four time-points, 80 patients had samples at three time-points, 83 patients had samples at two time points, and 72 patients had only a single sample available. The precollection sample was not examined separately for EFS and other associations, because it was obtained in such close proximity to the bone marrow collection. Samples for blood immunocytology were also obtained at diagnosis (n = 174), 4 weeks (n = 23), 12 weeks (n = 98), and at the time of bone marrow collection (n = 158).
The quantitation of tumor by immunocytology at the various time points used for analysis is shown for bone marrow and blood in Table 1 and Fig 1. Patient characteristics and the percentage of patients with positive samples by characteristic at the various time points for both blood and bone marrow immunocytology are listed in Table 2. The median age for these patients was 2.9 years, with a typical profile of clinical and biologic risk factors for children with stage IV neuroblastoma
Eighty-one percent of children had a positive bone marrow immunocytology at diagnosis, with a median bone marrow tumor burden for positive samples of 8,674 cells per 105 nucleated cells (Table 1). The concordance of light microscopic evidence of bone marrow metastases by the local institutional pathologist (which included bilateral aspirate and biopsy) with bone marrow immunocytology was 86%. Thirty-three bone marrow samples were negative by both evaluations, 196 were positive by both evaluations, and 38 (14%) were discordant. Eighteen marrow samples were positive by light microscopic evaluation and negative by immunocytology, whereas 20 were negative by light microscopic evaluation and positive by immunocytology. When the precollection and collection samples were compared using a quantitative cutoff of fewer than 100 versus 100 tumor cells per 105 bone marrow cells, they were 96% concordant in 171 patients. However, there was lower concordance (71%) when considering whether samples had only one or more tumor cell per 105 bone marrow cells, probably because of the much larger volume of the sample (100-fold) obtained at actual collection compared with that obtained at precollection.
The percentage of patients with any detectable bone marrow tumor by immunocytology steadily decreased during therapy, as shown in Fig 1, Table 1, and Table 2, from 81% of patients at diagnosis to 14% by the end of induction. If the cutoff of Children with high-risk stage III neuroblastoma were also entered on CCG-3891 (n = 72). Their results are not included in the analyses that follow in this article in order to have a uniform group of stage IV patients, but the immunocytology quantitation is given here for comparison. Immunocytology at diagnosis was positive in nine of 36 children with stage III disease, with a median tumor cell number of 7 per 105 nucleated cells, and blood immunocytology was positive in only two of 19 patients. Bone marrow immunocytology at 4 weeks was positive in two of 18, at 12 weeks in one of 27, at collection in 0 of 18, and at end induction in 0 of 23 patients. There was no significant difference in EFS by bone marrow immunocytology at diagnosis. Only one patient with stage III neuroblastoma had positive blood immunocytology at both 12 weeks and harvest, but not at the end of induction. This patient experienced relapse and died.
Immunocytology and Biologic and Clinical Risk Factors
Immunocytology and Prognosis
To test whether the patients with missing samples differed from those with immunocytology results, an analysis of EFS in these two subgroups was performed. There was no significant difference in EFS for patients with metastatic disease lacking immunocytology and those with this result available. Three-year EFS for those lacking an immunocytology sample at diagnosis compared with those with an immunocytology result using the log-rank test was 26% versus 27% (P = .21), 27% versus 25% at week 12 (P = .65), and 28% versus 32% at the end of induction (P = .19).
This adverse prognostic impact of bone marrow immunocytology Positive blood immunocytology at week 0 but not at collection (Fig 3) was correlated with decreased EFS. In contrast to the bone marrow results, the blood immunocytology at week 0 was no longer predictive (P > .9) in a model that included MYCN amplification.
When analyzed by treatment regimen, there was still an EFS advantage for patients with fewer than 100 tumor cells at diagnosis, 12 weeks, and at bone marrow collection, regardless of whether they were treated with ABMT or consolidation chemotherapy (Table 3). However, this was only significant (P < .05) in the 12-week (chemotherapy arm) or collection (ABMT arm) samples. There was not a significant difference in EFS for the subgroups of patients with either positive ( one tumor cell per 105) or negative immunocytology at any of the time points by consolidation regimen. The only difference for immunocytology after stratification by postconsolidation therapy (± 13-cis-retinoic acid) was for patients who had positive immunocytology at collection and were randomized to no postconsolidation therapy. The four patients with positive immunocytology ( one tumor cell) had a significantly lower EFS than those 52 with negative immunocytology (P = .037). After stratification by immunocytology, a relative though nonsignificant advantage in EFS was seen for those receiving 13-cis-retinoic acid, consistent with the overall benefit for this arm of the study.15
Next, in an attempt to discover whether the amount of change in immunocytology was significant, we examined EFS in patients whose paired bone marrow samples were grouped by changes from positive to negative compared with those who did not become negative. This analysis was limited by the numbers of patients who had paired samples at the various time points. For patients with any positive bone marrow immunocytology at diagnosis, regardless of the percentage, the EFS was not significantly different whether the tumor cells had cleared at 4 weeks or at 12 weeks. There was also no significant difference in the EFS for those patients whose immunocytology at 4 weeks was positive but at 12 weeks changed to negative, regardless of whether the cutoff of one tumor cell or 100 tumor cells was considered positive. We also examined the degree of decrease in marrow tumor cells by looking at groups who cleared 1, 2, or
Our data show that quantitative bone marrow immunocytology at diagnosis is a powerful prognostic factor in children with stage IV neuroblastoma. Moreover, this factor remains influential even after consideration of other known predictors of outcome, namely MYCN gene copy number,17 serum ferritin,16 and morphologic evidence of bone marrow involvement.1 This confirms and quantifies our previous observation that bone marrow is one of the unfavorable sites of metastases in stage IV neuroblastoma.1 We further have shown that patients with more than 100 tumor cells per 105 nucleated bone marrow cells after three to four cycles of chemotherapy had virtually no chance of survival, even with the myeloablative chemoradiotherapy and purged autologous bone marrow transplantation used in this study. Patients with a small number of persisting bone marrow tumor cells at the time of collection (< 100 per 105 nucleated bone marrow cells) did not have significantly different EFS than those with no detectable tumor. This suggests that the intensive pretransplantation conditioning or the consolidation therapy may be sufficient to eliminate small numbers of tumor cells, but not larger amounts. The fact that one half of the patients also received 13-cis-retinoic acid after consolidation may also have helped to eradicate small amounts of residual bone marrow tumor cells.15,27 However, the very small number of patients with detectable tumor cells in the bone marrow after consolidation or ABMT precluded the likelihood of seeing an impact of retinoid therapy on such patients. It is also possible that the reason patients with small numbers of bone marrow tumor cells did not have a different EFS than those without immunocytologically detectable tumor was due to the influence of sampling variability on tumor detection. This sampling dependence was suggested by the lower concordance of immediate precollection and collection immunocytology results in patients with small amounts of tumor cells. Thus there may have been some patients in the so-called negative group who had small pockets of microscopic tumor. Although the lack of immunocytology specimens for some patients at any given time point may have lessened the power of the analyses, the overall percentage of patients with metastatic disease on CCG-3891 who had a positive bone marrow at diagnosis by immunocytology (216 of 267 or 81%) or by morphology (374 of 466 or 80%) was similar, suggesting that there was nothing different about the group of patients for whom immunocytology results were not obtained. Furthermore, an analysis of EFS in patients with metastatic disease lacking immunocytology and those with this result available showed no significant difference at diagnosis (P = .21), week 12 (P = .65), or the end of induction (P = .19). The rapidity of the bone marrow response did not seem to be prognostic, as evidenced by a failure to correlate EFS with bone marrow immunocytology at week 4 after a single cycle of combination chemotherapy. Neither the conversion from positive to negative nor the extent of the change seemed to influence prognosis. This is different from the results reported for childhood acute lymphoblastic leukemia, where a day 14 and even a day 7 induction phase bone marrow are prognostic.28 Our data clearly demonstrate in a very large population of patients with metastatic neuroblastoma that circulating tumor cells in peripheral blood at diagnosis are extremely frequent, occurring in 58% of children. Eight patients had more than 1% tumor cells among their total nucleated cells circulating in blood. This study supports the preliminary observations of others demonstrating circulating tumor cells in the blood or in peripheral-blood stem-cell collections of some patients with neuroblastoma, using immunologic detection, clonogenic assays, and reverse-transcriptase polymerase chain reactions (RT-PCR).29-35 Our data show that detection of circulating tumor cells in peripheral blood at diagnosis is a significant unfavorable prognostic factor and, furthermore, is correlated with other high-risk features, including MYCN amplification and elevated serum ferritin. The data also show, not surprisingly, that circulating tumor cells are more likely to be found in patients with bone marrow metastases. Such peripheral-blood tumor cells persisted in a small percentage of patients even after multiple courses of chemotherapy, with little decrease subsequent to the first cycle of chemotherapy. This suggests that peripheral-blood stem-cell collections could be performed early in the course of treatment without increased risk of tumor contamination. However, the persistence of tumor cells in some patients emphasizes the importance of testing peripheral-blood stem-cell collections for tumor by sensitive methods before reinfusion and raises the question of the need for specific tumor-cell purging of stem-cell products. RT-PCR may increase the sensitivity of testing and provide an additional way to monitor circulating tumor cells.29,33-35 Parallel testing of RT-PCR, which may be an overly sensitive method, will be necessary together with immunocytology to determine which method is more valid for prediction of outcome. In conclusion, quantifying tumor cells in peripheral blood and bone marrow at diagnosis and during induction therapy is an important prognostic factor for patients with stage IV neuroblastoma. Moreover, bone marrow immunocytology seems to provide independent prognostic information for this group of patients, beyond other known predictors such as MYCN copy number and serum ferritin. The frequency of circulating tumor cells also suggests the possible need for tumor purging when peripheral-blood stem cells are used for hematopoietic support. Failure to reduce tumor cells in bone marrow to fewer than 100 tumor cells per 105 bone marrow cells within 12 weeks of beginning treatment is a very unfavorable prognostic sign using current therapeutic approaches and may provide a surrogate marker to detect patients who should be changed from standard therapy to an alternative, innovative treatment with greater potential to improve outcome.
Supported by grants to the Childrens Cancer Group (CA13539) and R.C.S. (CA22794, CA02649, CA60104) from the Division of Cancer Treatment, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD; from the Neil Bogart Memorial Laboratories of the T.J. Martell Foundation for Leukemia, Cancer, and AIDS Research, Los Angeles, CA, and New York, NY (C.P.R., R.C.S.); and from the Campini Foundation, Neuroblastoma Research Fund, and Conner Fund, San Francisco, CA (K.K.M.). We thank Carolyn Billups and Debra Collins for outstanding technical assistance.
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