http://repub.eur.nl/res/aut/4438/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/33207/ 2011-12-01T00:00:00Z The efficacy of azacitidine in the treatment of high-risk myelodysplastic syndromes (MDS), chronic myelomonocytic leukaemia (CMML) and acute myeloid leukaemia (AML) (20-30% blasts) has been demonstrated. To investigate the efficacy of azacitidine in daily clinical practice and to identify predictors for response, we analysed a cohort of 90 MDS, CMML and AML patients who have been treated in a Dutch compassionate named patient programme. Patients received azacitidine for a median of five cycles (range 1-19). The overall response rate (complete/partial/haematological improvement) was 57% in low risk MDS, 53% in high risk MDS, 50% in CMML, and 39% in AML patients. Median overall survival (OS) was 13·0 (9·8-16·2) months. Multivariate analysis confirmed circulating blasts [Hazard Ratio (HR) 0·48, 95% confidence interval (CI) 0·24-0·99; P=0·05] and poor risk cytogenetics (HR 0·45, 95% CI 0·22-0·91; P=0·03) as independent predictors for OS. Interestingly, this analysis also identified platelet doubling after the first cycle of azacitidine as a simple and independent positive predictor for OS (HR 5·4, 95% CI 0·73-39·9; P=0·10). In conclusion, routine administration of azacitidine to patients with variable risk groups of MDS, CMML and AML is feasible, and subgroups with distinct efficacy of azacitidine treatment can be identified. http://repub.eur.nl/res/pub/26795/ 2011-10-01T00:00:00Z Background Fms-like tyrosine kinase-3 (FLT3) gene mutations are frequent in acute promyelocytic leukemia but their prognostic value is not well established. Design and Methods We evaluated FLT3-internal tandem duplication and FLT3-D835 mutations in patients treated with all-trans retinoic acid and anthracycline-based chemotherapy enrolled in two subsequent trials of the Programa de Estudio y Tratamiento de las Hemopatías Malignas (PETHEMA) and Hemato-Oncologie voor Volwassenen Nederland (HOVON) groups between 1996 and 2005. Results FLT3-internal tandem duplication and FLT3-D835 mutation status was available for 306 (41%) and 213 (29%) patients, respectively. Sixty-eight (22%) and 20 (9%) patients had internal tandem duplication and D835 mutations, respectively. Internal tandem duplication was correlated with higher white blood cell and blast counts, lactate dehydrogenase, relapse-risk score, fever, hemorrhage, coagulopathy, BCR3 isoform, M3 variant subtype, and expression of CD2, CD34, human leukocyte antigen-DR, and CD11b surface antigens. The FLT3-D835 mutation was not significantly associated with any clinical or biological characteristic. Univariate analysis showed higher relapse and lower survival rates in patients with a FLT3-internal tandem duplication, while no impact was observed in relation to FLT3-D835. The prognostic value of the FLT3-internal tandem duplication was not retained in the multivariate analysis. Conclusions FLT3-internal tandem duplication mutations are associated with several hematologic features in acute promyelocytic leukemia, in particular with high white blood cell counts, but we were unable to demonstrate an independent prognostic value in patients with acute promyelocytic leukemia treated with all-trans retinoic acid and anthracycline-based regimens. http://repub.eur.nl/res/pub/30999/ 2011-09-01T00:00:00Z Background: High white blood cell count at presentation is an unfavorable prognostic factor for treatment outcome in intermediate cytogenetic risk acute myeloid leukemia. Since the impact of white blood cell count on outcome of subgroups defined by the molecular markers NPMc+and FLT3- internal tandem duplication (ITD) is unknown, we addressed this issue. Design and Methods: We studied the effect of white blood cell count on outcome in a clinically and molecularly welldefined cohort of 525 patients with acute myeloid leukemia using these molecular markers. In addition, since an increased white blood cell count has been associated with an increased FLT3- ITD/FLT3 (wild-type) ratio, we investigated whether the effect of white blood cell count on outcome could be explained by the FLT3-ITD/FLT3 ratio. Results: This analysis revealed that white blood cell count had no impact on outcome in patients with the genotypic combinations 'NPMc+without FLT3-ITD' and 'NPM1 wild-type with or without FLT3-ITD'. In contrast, white blood cell count had a significant impact on complete remission rate (P=0.034), event-free survival (P=0.009) and overall survival (P<0.001) in patients with the genotypic combination 'NPMc+with FLT3-ITD'. A FLT3-ITD/FLT3 ratio greater than 1 was also associated with a reduced complete remission rate (P=0.066) and significantly reduced eventfree survival (P= 0.001) and overall survival (P=0.001) in patients with the genotypic combination 'NPMc+with FLT3-ITD'. Multivariable analysis revealed that white blood cell count and FLT3-ITD/FLT3 ratio were independent prognostic indicators for outcome in the subgroup with the genotypic combination 'NPMc+with FLT3-ITD'. Conclusions: Our results demonstrate that both high white blood cell count and FLT3-ITD/FLT3 ratio are prognostic factors in patients with acute myeloid leukemia with the genotypic combination 'NPMc+with FLT3-ITD'. http://repub.eur.nl/res/pub/25150/ 2011-03-17T00:00:00Z BACKGROUND: Cytarabine (ara-C) is an important drug in the treatment of acute myeloid leukemia (AML). High-dose cytarabine (2000 to 3000 mg per square meter of body-surface area) is toxic but results in higher rates of relapse-free survival than does the conventional dose of 100 to 400 mg per square meter. Intermediate dose levels have not been thoroughly evaluated. METHODS: We compared two induction regimens in patients 18 to 60 years of age (median, 49) who had newly diagnosed AML. The intermediate-dose group, totaling 431 patients, received cytarabine at a dose of 200 mg per square meter given by continuous intravenous infusion for 24 hours during cycle 1 of induction therapy and 1000 mg per square meter by infusion for 3 hours twice daily during cycle 2 of induction therapy. The high-dose group, totaling 429 patients, received a dose-escalated regimen of 1000 mg of cytarabine per square meter every 12 hours in cycle 1 and 2000 mg per square meter twice daily in cycle 2. Patients with a complete response did not receive additional cytarabine but received consolidation therapy in a third cycle of chemotherapy (mitoxantrone-etoposide) or underwent autologous or allogeneic stem-cell transplantation. Complete remission rates, survival rates, and toxic effects were assessed for each treatment group. RESULTS: At a median follow-up of 5 years, no significant differences were noted between the intermediate-dose group and the high-dose group with respect to complete remission rates (80% and 82%, respectively), probability of relapse, event-free survival at 5 years (34% and 35%), or overall survival (40% and 42%). High-dose cytarabine provided no clear advantage in any prognostic subgroup. The high-dose treatment resulted in higher incidences of grade 3 and grade 4 toxic effects (in cycle 1), prolonged hospitalization, and delayed neutrophil recovery (in cycle 2) and platelet recovery (in cycles 2 and 3). CONCLUSIONS: Induction therapy with cytarabine at the lower dose already produced maximal antileukemic effects for all response end points, suggesting a plateau in the dose-response relationship above this dose level. High-dose cytarabine results in excessive toxic effects without therapeutic benefit. (Netherlands Trial Register number, NTR230.). Copyright http://repub.eur.nl/res/pub/22849/ 2011-02-10T00:00:00Z The expression of CD56 antigen in acute promyelocytic leukemia (APL) blasts has been associated with short remission duration and extramedullary relapse. We investigated the clinical significance of CD56 expression in a large series of patients with APL treated with all-trans retinoic acid and anthracycline-based regimens. Between 1996 and 2009, 651 APL patients with available data on CD56 expression were included in 3 subsequent trials (PETHEMA LPA96 and LPA99 and PETHEMA/HOVON LPA2005). Seventytwo patients (11%) were CD56+ (expression of CD56 in ≥20% leukemic promyelocytes). CD56+ APL was significantly associated with high white blood cell counts; low albumin levels; BCR3 isoform; and the coexpression of CD2, CD34, CD7, HLA-DR, CD15, and CD117 antigens. For CD56+ APL, the 5-year relapse rate was 22%, compared with a 10% relapse rate for CD56- APL (P = .006). In the multivariate analysis, CD56 expression retained the statistical significance together with the relapse-risk score. CD56+ APLalso showed a greater risk of extramedullary relapse (P < .001). In summary, CD56 expression is associated with the coexpression of immaturity-associated and T-cell antigens and is an independent adverse prognostic factor for relapse in patients with APL treated with all-trans-retinoic acid plus idarubicin - derived regimens. This marker may be considered for implementing riskadapted therapeutic strategies in APL. The LPA2005 trial is registered at http://www.clinicaltrials.gov as NCT00408278. http://repub.eur.nl/res/pub/23647/ 2010-04-01T00:00:00Z Abstract: In older patients with acute myeloid leukemia (AML), the prevention of relapse has remained one of the major therapeutic challenges, with more than 75% relapses after complete remission. The anti-CD33 immunotoxin conjugate gemtuzumab ozogamicin (GO) has shown antileukemic remission induction activity in patients with relapsed AML. Patients with AML or refractory anemia with excess blasts in first complete remission attained after intensive induction chemotherapy were randomized between 3 cycles of GO (6 mg/m(2) every 4 weeks) or no postremission therapy (control) to assess whether GO would improve outcome. The 2 treatment groups (113 patients receiving GO vs 119 control patients) were comparable with regard to age (60-78 years, median 67 years), performance status, and cytogenetics. A total of 110 of 113 received at least 1 cycle of GO, and 65 of 113 patients completed the 3 cycles. Premature discontinuation was mainly attributable to incomplete hematologic recovery or intercurrent relapse. Median time to recovery of platelets 50 x 10(9)/L and neutrophils 0.5 x 10(9)/L after GO was 14 days and 20 days. Nonhematologic toxicities were mild overall, but there was 1 toxic death caused by liver failure. There were no significant differences between both treatment groups with regard to relapse probabilities, nonrelapse mortality, overall survival, or disease-free survival (17% vs 16% at 5 years). Postremission treatment with GO in older AML patients does not provide benefits regarding any clinical end points. The HOVON-43 study is registered at The Netherlands Trial Registry (number NTR212) and at http://www.controlled-trials.com as ISRCTN77039377. http://repub.eur.nl/res/pub/26805/ 2010-03-01T00:00:00Z Background: Acute promyelocytic leukemia is a subtype of acute myeloid leukemia characterized by the t(15;17). The incidence and prognostic significance of additional chromosomal abnormalities in acute promyelocytic leukemia is still a controversial matter. Design and Methods: Based on cytogenetic data available for 495 patients with acute promyelocytic leukemia enrolled in two consecutive PETHEMA trials (LPA96 and LPA99), we analyzed the incidence, characteristics, and outcome of patients with acute promyelocytic leukemia with and without additional chromosomal abnormalities who had been treated with all-trans retinoic acid plus anthracycline monochemotherapy for induction and consolidation. Results: Additional chromosomal abnormalities were observed in 140 patients (28%). Trisomy 8 was the most frequent abnormality (36%), followed by abn(7q) (5%). Patients with additional chromosomal abnormalities more frequently had coagulopathy (P=0.03), lower platelet counts (P=0.02), and higher relapse-risk scores (P=0.02) than their counterparts without additional abnormalities. No significant association with FLT3/ITD or other clinicopathological characteristics was demonstrated. Patients with and without additional chromosomal abnormalities had similar complete remission rates (90% and 91%, respectively). Univariate analysis showed that additional chromosomal abnormalities were associated with a lower relapse-free survival in the LPA99 trial (P=0.04), but not in the LPA96 trial. However, neither additional chromosomal abnormalities overall nor any specific abnormality was identified as an independent risk factor for relapse in multivariate analysis. Conclusions: The lack of independent prognostic value of additional chromosomal abnormalities in acute promyelocytic leukemia does not support the use of alternative therapeutic strategies when such abnormalities are found. http://repub.eur.nl/res/pub/27457/ 2010-02-11T00:00:00Z The phase 3 trial HOVON-50 was designed to evaluate the effect of thalidomide during induction treatment and as maintenance in patients with multiple myeloma who were transplant candidates. A total of 556 patients was randomly assigned to arm A: 3 cycles of vincristine, adriamycin, and dexamethasone, or to arm B: thalidomide 200 mg orally, days 1 to 28 plus adriamycin and dexamethasone. After induction therapy and stem cell mobilization, patients were to receive high-dose melphalan, 200 mg/m2, followed by maintenance with α-interferon (arm A) or thalidomide 50 mg daily (arm B). Thalidomide significantly improved overall response rate as well as quality of the response before and after high dose melphalan. Best overall response rate on protocol was 88% and 79% (P = .005), at least very good partial remission 66% and 54% (P = .005), and complete remission 31% and 23% (P = .04), respectively, in favor of the thalidomide arm. Thalidomide also significantly improved event-free survival from median 22 months to 34 months (P < .001), and prolonged progression free from median 25 months to 34 months (P < .001). Median survival was longer in the thalidomide arm, 73 versus 60 months; however, this difference was not significant (P = .77). Patients randomized to thalidomide had strongly reduced survival after relapse. This trial was registered on www.controlled-trials.com as ISRCTN06413384. http://repub.eur.nl/res/pub/25329/ 2009-11-19T00:00:00Z Acute myeloid leukemia (AML) has a different clinical and biologic behavior in patients at older age. To gain further insight into the molecular differences, we examined a cohort of 525 adults to compare gene expression profiles of the one-third of youngest cases (n = 175; median age 31 years) with the one-third of oldest cases (n = 175; median age 59 years). This analysis revealed that 477 probe sets were up-regulated and 492 probe sets were down-regulated with increasing age at the significance level of P < .00001. After validation with 2 independent AML cohorts, the 969 differentially regulated probe sets on aging could be pointed to 41 probe sets, including the tumor-suppressor gene CDKN2A (encoding p16INK4A). In contrast to the induced p16INK4Aexpression that is associated with physiologic aging, p16INK4Ais down-regulated in AML samples of patients with increasing age. However, this was only noticed in the intermediate- and unfavorable-risk group and not in the favorable-risk group and the molecularly defined subset "NPM1 mutant without FLT3-ITD." Multivariate analysis revealed p16INK4A, besides cytogenetic risk groups, as an independent prognostic parameter for overall survival in older patients. We conclude that, in addition to altered clinical and biologic characteristics, AML presenting at older age shows different gene expression profiles. http://repub.eur.nl/res/pub/26809/ 2009-09-24T00:00:00Z BACKGROUND: A complete remission is essential for prolonging survival in patients with acute myeloid leukemia (AML). Daunorubicin is a cornerstone of the induction regimen, but the optimal dose is unknown. In older patients, it is usual to give daunorubicin at a dose of 45 to 50 mg per square meter of body-surface area. METHODS: Patients in whom AML or high-risk refractory anemia had been newly diagnosed and who were 60 to 83 years of age (median, 67) were randomly assigned to receive cytarabine, at a dose of 200 mg per square meter by continuous infusion for 7 days, plus daunorubicin for 3 days, either at the conventional dose of 45 mg per square meter (411 patients) or at an escalated dose of 90 mg per square meter (402 patients); this treatment was followed by a second cycle of cytarabine at a dose of 1000 mg per square meter for 6 days. The primary end point was event-free survival. RESULTS: The complete remission rates were 64% in the group that received the escalated dose of daunorubicin and 54% in the group that received the conventional dose (P = 0.002); the rates of remission after the first cycle of induction treatment were 52% and 35%, respectively (P<0.001). There was no significant difference between the two groups in the incidence of hematologic toxic effects, 30-day mortality (11% and 12% in the two groups, respectively), or the incidence of moderate, severe, or life-threatening adverse events (P = 0.08). Survival end points in the two groups did not differ significantly overall, but patients in the escalated-treatment group who were 60 to 65 years of age, as compared with the patients in the same age group who received the conventional dose, had higher rates of complete remission (73% vs. 51%), event-free survival (29% vs. 14%), and overall survival (38% vs. 23%). CONCLUSIONS: In patients with AML who are older than 60 years of age, escalation of the dose of daunorubicin to twice the conventional dose, with the entire dose administered in the first induction cycle, effects a more rapid response and a higher response rate than does the conventional dose, without additional toxic effects. (Current Controlled Trials number, ISRCTN77039377; and Netherlands National Trial Register number, NTR212.) Copyright http://repub.eur.nl/res/pub/19339/ 2009-01-22T00:00:00Z Differentiation syndrome (DS) can be a life-threatening complication in patients with acute promyelocytic leukemia (APL) undergoing induction therapy with all- trans retinoic acid (ATRA). Detailed knowl- edge about DS has remained limited. We present an analysis of the incidence, char- acteristics, prognostic factors, and out- come of 739 APL patients treated with ATRA plus idarubicin in 2 consecutive trials (Programa Espanol de Tratamientos en Hematologíc [PETHEMA] LPA96 and LPA99). Overall, 183 patients (24.8%) ex- perienced DS, 93 with a severe form (12.6%) and 90 with a moderate form (12.2%). Severe but not moderate DS was associated with an increase in mortality. A bimodal incidence of DS was observed, with peaks occurring in the first and third weeks after the start of ATRA therapy. A multivariate analysis indicated that a WBC count greater than 5 x 109/L and an abnor- mal serum creatinine level correlated with an increased risk of developing severe DS. Patients receiving systematic pred- nisone prophylaxis (LPA99 trial) in con- trast to those receiving selective prophy- laxis with dexamethasone (LPA96 trial) had a lower incidence of severe DS. Pa- tients developing severe DS showed a reduced 7-year relapse-free survival in the LPA96 trial (60% vs 85%, P = .003), but this difference was not apparent in the LPA99 trial. http://repub.eur.nl/res/pub/28934/ 2008-10-15T00:00:00Z A previous report of the Programa de Estudio y Tratamiento de las Hemopatfas Malignas (PETHEMA) Group showed that a risk-adapted strategy combining all-trans retinoic acid (ATRA) and anthracycline monochemotherapy for induction and consolidation in newly diagnosed acute promyelocytic leukemia results in an improved outcome. Here we analyze treatment outcome of an enlarged series of patients who have been followed up for a median of 65 months. From November 1999 through July 2005 (LPA99 trial), 560 patients received induction therapy with ATRA plus idarubicin. Patients achieving complete remission received 3 courses of consolidation followed by maintenance with ATRA and low-dose chemotherapy. The 5-year cumulative incidence of relapse and disease-free survival were 11% and 84%, respectively. These results compare favorably with those obtained in the previous LPA96 study (P=.019 and P=.04, respectively). This updated analysis confirms the high antileukemic efficacy, low toxicity, and high degree of compliance of a riskadapted strategy combining ATRA and anthracycline monochemotherapy for consolidation therapy. http://repub.eur.nl/res/pub/28818/ 2008-04-01T00:00:00Z An understanding of the prognostic factors associated with the various forms of induction mortality in patients with acute promyelocytic leukemia (APL) has remained remarkably limited. This study reports the incidence, time of occurrence, and prognostic factors of the major categories of induction failure in a series of 732 patients of all ages (range, 2-83 years) with newly diagnosed APL who received all-trans retinoic acid (ATRA) plus idarubicin as induction therapy in 2 consecutive studies of the Programa de Estudio y Tratamiento de las Hemopatias Malignas (PETHEMA) Group. Complete remission was attained in 666 patients (91%). All the 66 induction failures were due to induction death. Hemorrhage was the most common cause of induction death (5%), followed by infection (2.3%) and differentiation syndrome (1.4%). Multivariate analysis identified specific and distinct pretreatment characteristics to correlate with an increased risk of death caused by hemorrhage (abnormal creatinine level, increased peripheral blast counts, and presence of coagulopathy), infection (age >60 years, male sex, and fever at presentation), and differentiation syndrome (Eastern Cooperative Oncology Group [ECOG] score >1 and low albumin levels), respectively. These data furnish clinically relevant information that might be useful for designing more appropriately risk-adapted treatment protocols aimed at reducing the considerable problem of induction mortality in APL. http://repub.eur.nl/res/pub/28745/ 2008-01-15T00:00:00Z We evaluated the role of rituximab during remission induction chemotherapy in relapsed aggressive CD20+non-Hodgkin lymphoma. Of 239 patients, 225 were evaluable for analysis. Randomized to DHAP (cisplatin-cytarabine- dexamethasone)-VIM (etoposide-ifosfamide-methotrexate)-DHAP (cisplatin- cytarabine-dexamethasone) chemotherapy with rituximab (R; R-DHAP arm) were 119 patients (113 evaluable) and to chemotherapy without rituximab (DHAP arm) 120 patients (112 evaluable). Patients in complete remission (CR) and partial remission (PR) after 2 chemotherapy courses were eligible for autologous stem-cell transplantation. After the second chemotherapy cycle, 75% of the patients in the R-DHAP arm had responsive disease (CR or PR) versus 54% in the DHAP arm (P = .01). With a median follow-up of 24 months, there was a significant difference in failure-free survival (FFS24; 50% vs 24% vs, P < .001), and progression free survival (PFS24; 52% vs 31% P < .002) in favor of the R-DHAP arm. Cox-regression analysis demonstrated a significant effect of rituximab treatment on FFS24(HR 0.41, 95% confidence interval [CI] 0.29-0.57 versus 0.51, 95% CI 0.37-0.70) and overall-survival (OS24: HR 0.60 [0.41-0.89] vs 0.76 [0.52-1.10]) when adjusted for time since upfront treatment, age, World Health Organization performance status, and secondary age-adjusted international prognostic index. These results demonstrate improved FFS and PFS for relapsed aggressive B-cell NHLif rituximab is added to the re-induction chemotherapy regimen. http://repub.eur.nl/res/pub/8251/ 2005-01-01T00:00:00Z To determine whether MDR1 reversal by the addition of the P-glycoprotein (P-gp) inhibitor PSC-833 to standard induction chemotherapy would improve event-free survival (EFS), 419 untreated patients with acute myeloid leukemia (AML) aged 60 years and older were randomized to receive 2 induction cycles of daunorubicin and cytarabine with or without PSC-833. Patients in complete remission were then given 1 consolidation cycle without PSC-833. Neither complete response (CR) rate (54% versus 48%; P = .22), 5-year EFS (7% versus 8%; P = .53), disease-free survival (DFS; 13% versus 17%; P = .06) nor overall survival (OS; 10% in both arms; P = .52) were significantly improved in the PSC-833 arm. An integrated P-gp score (IPS) was determined based on P-gp function and P-gp expression in AML cells obtained prior to treatment. A higher IPS was associated with a significantly lower CR rate and worse EFS and OS. There was no significant interaction between IPS and treatment arm with respect to CR rate and survival, indicating also a lack of benefit of PSC-833 in P-gp-positive patients. The role of strategies aimed at inhibitory P-gp and other drug-resistance mechanisms continues to be defined in the treatment of patients with AML. http://repub.eur.nl/res/pub/8236/ 2003-01-01T00:00:00Z We compared the efficacy of intensified chemotherapy followed by myeloablative therapy and autologous stem cell rescue with intensified chemotherapy alone in patients newly diagnosed with multiple myeloma. There were 261 eligible patients younger than 66 years with stage II/III multiple myeloma who were randomized after remission induction therapy with vincristine, adriamycin, dexamethasone (VAD) to receive intensified chemotherapy, that is, melphalan 140 mg/m(2) administered intravenously in 2 doses of 70 mg/m(2) (intermediate-dose melphalan [IDM]) without stem cell rescue (n = 129) or the same regimen followed by myeloablative therapy consisting of cyclophosphamide, total body irradiation, and autologous stem cell reinfusion (n = 132). Interferon-alpha-2a was given as maintenance. Of the eligible patients, 79% received both cycles of IDM and 79% of allocated patients actually received myeloablative treatment. The response rate (complete remission [CR] plus partial remission [PR]) was 88% in the intensified chemotherapy group versus 95% in the myeloablative treatment group. CR was significantly higher after myeloablative therapy (13% versus 29%; P =.002). With a median follow-up of 33 months (range, 8-65 months), the event-free survival (EFS) was not different between the treatments (median 21 months versus 22 months; P =.28). Time to progression (TTP) was significantly longer after myeloablative treatment (25 months versus 31 months; P =.04). The overall survival (OS) was not different (50 months versus 47 months; P =.41). Intensified chemotherapy followed by myeloablative therapy as first-line treatment for multiple myeloma resulted in a higher CR and a longer TTP when compared with intensified chemotherapy alone. However, it did not result in a better EFS and OS. http://repub.eur.nl/res/pub/9419/ 2000-01-01T00:00:00Z Recently the Belgium-Dutch Hematology-Oncology group initiated a multicenter study to evaluate whether myeloma patients treated with intensive chemotherapy benefit from additional peripheral stem cell transplantation. To determine treatment response accurately, we decided to quantitate malignant cells. To test a consensus quantitation strategy, 5 centers independently determined the immunoglobulin heavy chain sequences of patient tumor cells and developed allele-specific oligonucleotides (ASO) and ASO-polymerase chain reaction (PCR). We compared the reproducibility of real-time quantitation with quantitation using limiting dilutions. We distributed DNA samples with a 4-log range of tumor cell concentrations and found average quantitation values deviating 74% and 42% from the input values with real-time PCR (1 center) and limiting dilutions (4 centers), respectively. Within single centers we found an average variation coefficient of 0.74, with limiting dilutions not significantly different from the average 0.82 center-to-center variation coefficient. Within a single center, real-time quantitation proved more reproducible (average variation coefficient, 0.36). Quantification was confirmed in 3 patients during treatment in the protocol. This report shows that real-time PCR or limiting dilution assays can be used for quantitation in a single multicenter trial. We present a consensus strategy that allows an accurate comparison of quantitation data generated in independent centers.