Adjuvant Gemcitabine Versus Neoadjuvant/Adjuvant FOLFIRINOX in Resectable Pancreatic Cancer: The Randomized Multicenter Phase II NEPAFOX Trial

BACKGROUND

Although addition of adjuvant chemotherapy is the current standard, the prognosis of pancreatic cancers still remains poor. The NEPAFOX trial evaluated perioperative treatment with FOLFIRINOX in resectable pancreatic cancer.

PATIENTS AND METHODS

This multicenter phase II trial randomized patients with resectable or borderline resectable pancreatic cancer without metastases into arm (A,) upfront surgery plus adjuvant gemcitabine, or arm (B,) perioperative FOLFIRINOX. The primary endpoint was overall survival (OS).

RESULTS

Owing to poor accrual, recruitment was prematurely stopped after randomization of 40 of the planned 126 patients (A: 21, B: 19). Overall, approximately three-quarters were classified as primarily resectable (A: 16, B: 15), and the remaining patients were classified as borderline resectable (A: 5, B: 4). Of the 12 evaluable patients, 3 achieved partial response under neoadjuvant FOLFIRINOX. Of the 21 patients in arm A and 19 patients in arm B, 17 and 7 underwent curative surgery, and R0-resection was achieved in 77% and 71%, respectively. Perioperative morbidity occurred in 72% in arm A and 46% in arm B, whereas non-surgical toxicity was comparable in both arms. Median RFS/PFS was almost doubled in arm B (14.1 months) compared with arm A (8.4 months) in the population with surgical resection, whereas median OS was comparable between both arms.

CONCLUSIONS

Although the analysis was only descriptive owing to small patient numbers, no safety issues regarding surgical complications were observed in the perioperative FOLFIRINOX arm. Thus, considering the small number of patients, perioperative treatment approach appears feasible and potentially effective in well-selected cohorts of patients. In pancreatic cancer, patient selection before initiation of neoadjuvant therapy appears to be critical.

Evaluation of clinical parameters and biomarkers in older, untreated mantle cell lymphoma patients receiving bendamustine-rituximab

Mantle cell lymphoma (MCL) is clinically and biologically heterogeneous. While various prognostic features have been proposed, none currently impact therapy selection, particularly in older patients, for whom treatment is primarily dictated by age and comorbidities. Herein, we undertook a comprehensive comparison of clinicopathological features in a cohort of patients 60 years and older, uniformly treated with bendamustine and rituximab, with a median survival of >8 years. The strongest prognostic indicators in this cohort were a high-risk call by a simplified MCL international prognostic index (s-MIPI) (HR: 3.32, 95% CI: 1.65-6.68 compared to low risk), a high-risk call by MCL35 (HR: 10.34, 95% CI: 2.37-45.20 compared to low risk) and blastoid cytology (HR: 4.21, 95% CR: 1.92-9.22 compared to classic). Patients called high risk by both the s-MIPI and MCL35 had the most dismal prognosis (HR: 11.58, 95% CI: 4.10-32.72), while those with high risk by either had a moderate but clinically relevant prognosis (HR: 2.95, 95% CI: 1.49-5.82). A robust assay to assess proliferation, such as MCL35, along with stringent guidelines for cytological evaluation of MCL, in combination with MIPI, may be a strong path to risk-stratify older MCL patients in future clinical trials.

Q-HAM: a multicenter upfront randomized phase II trial of quizartinib and high-dose Ara-C plus mitoxantrone in relapsed/refractory AML with FLT3-ITD

BACKGROUND

About 50% of older patients with acute myeloid leukemia (AML) fail to attain complete remission (CR) following cytarabine plus anthracycline-based induction therapy. Salvage chemotherapy regimens are based on high-dose cytarabine (HiDAC), which is frequently combined with mitoxantrone (HAM regimen). However, CR rates remain low, with less than one-third of the patients achieving a CR. FLT3-ITD has consistently been identified as an unfavorable molecular marker in both relapsed and refractory (r/r)-AML. One-quarter of patients who received midostaurin are refractory to induction therapy and relapse rate at 2 years exceeds 40%. The oral second-generation bis-aryl urea tyrosine kinase inhibitor quizartinib is a very selective FLT3 inhibitor, has a high capacity for sustained FLT3 inhibition, and has an acceptable toxicity profile.

METHODS

In this multicenter, upfront randomized phase II trial, all patients receive quizartinib combined with HAM (cytarabine 3g/m2 bidaily day one to day three, mitoxantrone 10mg/m2 days two and three) during salvage therapy. Efficacy is assessed by comparison to historical controls based on the matched threshold crossing approach with achievement of CR, complete remission with incomplete hematologic recovery (CRi), or complete remission with partial recovery of peripheral blood counts (CRh) as primary endpoint. During consolidation therapy (chemotherapy and allogeneic hematopoietic cell transplantation), patients receive either prophylactic quizartinib therapy or measurable residual disease (MRD)-triggered preemptive continuation therapy with quizartinib according to up-front randomization. The matched threshold crossing approach is a novel study-design to enhance the classic single-arm trial design by including matched historical controls from previous clinical studies. It overcomes common disadvantages of single-armed and small randomized studies, since the expected outcome of the observed study population can be adjusted based on the matched controls with a comparable distribution of known prognostic and predictive factors. Furthermore, balanced treatment groups lead to stable statistical models. However, one of the limitations of our study is the inability to adjust for unobserved or unknown confounders. Addressing the primary endpoint, CR/CRi/CRh after salvage therapy, the maximal sample size of 80 patients is assessed generating a desirable power of the used adaptive design, assuming a logistic regression is performed at a one-sided significance level α=0.05, the aspired power is 0.8, and the number of matching partners per intervention patient is at least 1. After enrolling 20 patients, the trial sample size will be recalculated in an interim analysis based on a conditional power argument.

CONCLUSION

Currently, there is no commonly accepted standard for salvage chemotherapy treatment. The objective of the salvage therapy is to reduce leukemic burden, achieve the best possible remission, and perform a hemopoietic stem-cell transplantation. Thus, in patients with FLT3-ITD mutation, the comparison of quizartinib with intensive salvage therapy versus chemotherapy alone appears as a logical consequence in terms of efficacy and safety.

ETHICS AND DISSEMINATION

Ethical approval and approvals from the local and federal competent authorities were granted. Trial results will be reported via peer-reviewed journals and presented at conferences and scientific meetings.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03989713; EudraCT Number: 2018-002675-17.

Randomized multicenter phase II/III study with adjuvant gemcitabine versus neoadjuvant/adjuvant FOLFIRINOX in resectable pancreatic cancer: The NEPAFOX trial

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Background: The outcome of pancreatic cancer remains poor. Few patients (pts) can be assigned to surgery and 80% of resected pts experience a relapse. Currently, adjuvant ctx is standard, but prognosis remains poor. FOLFIRINOX (FFX) is a SOC in metastatic and meanwhile in the adjuvant setting and may represent a valuable neoadjuvant option in resectable and borderline resectable stages. We initiated the NEPAFOX– trial in Germany to explore the efficacy of perioperative FFX. Methods: This is a multicenter randomized phase II/III trial. Recruitment of the trial was stopped after 40 patients (pts) due to poor accrual. Pts with resectable or borderline resectable adenocarcinoma of the pancreas without metastases were eligible. Eligible pts were randomized to (arm A) upfront surgery followed by adjuvant gemcitabine (1000 mg/m2) for 6 months or (arm B) perioperative FFX (irinotecan 180 mg/m2, oxaliplatin 85 mg/m2, 5-FU 400mg/m² bolus, 5-FU 2400 mg/m², sodium folinate 400 mg/m2) 4-6 cycles (8-12 weeks) pre and further 4-6 cycles post surgery. The primary endpoint is OS. Secondary endpoints include PFS, perioperative morbidity, mortality, and others. Results: 40 pts (42.5% female) were randomized over 3 years (05.03.2015 FPI - 23.03.2018 LPI), 21 in arm A, 19 in arm B. Age range was 46-84y, median age 64y.Before randomization, 76.2% of the pts in Arm A and 78.9% in Arm B were classified as primarily resectable the remaining pts as borderline resectable. Patients received in median 3 cycles in Arm A (range: 0-6) and 6 in Arm B (range: 1-12). Surgery was performed in 18 pts (85.7%) in Arm A and 11 (57.9%) in Arm B. Reasons for not conducting surgery were for Arm A patient´s wish (1 pt) and inoperability (2 pts), for Arm B early progressive disease (4 pts), death (1 pt), pneumonia (1 pt), and toxicities (1 pt). 13 (Arm A) and 5 (Arm B) pts had a R0-Resection. Perioperative morbidity occurred in 72.2% of operated pts in Arm A and 45.5% in Arm B. Median OS was 25.68 months in Arm A (6 events of death) and 10.03 months in Arm B (14 events) with HR 0.366 and p = 0.0337. Median PFS was 9.8 months in Arm A (12 events) and 6.64 months in Arm B (16 events) with HR 0.722 and p = 0.4099. Conclusions: Due to low pt numbers, the analyses for primary and secondary endpoints are not robust and only descriptive. Median OS for Gemcitabine- arm was in the line with literature data and better than for FFX, but pt/event numbers are too for conclusion. Only 11 out of 19 FFX pts underwent surgery, only 9 pts had pancreatic resection, indicating that pts should be extremely good selected before starting a neoadjuvant approach. According to CT or MRI pts of arm B were not more advanced regarding tumor staging. Nevertheless, there were no safety issues in the FFX arm regarding surgical complications, so neoadjuvant/ perioperative treatment approach seems to be feasible, subjected to the small number of pts in the study. Clinical trial information: NCT02172976.

Quality of life and outcome of patients with metastatic pancreatic cancer receiving first-line chemotherapy with nab-paclitaxel and gemcitabine: Real-life results from the prospective QOLIXANE trial of the Platform for Outcome, Quality of Life and Translational Research on Pancreatic Cancer registry

Few data exist on health-related quality of life (QoL) in patients with metastatic pancreatic cancer (mPC) receiving first-line chemotherapy (Awad L ZE, Mesbah M Boston, MA. Applying survival data methodology to analyze quality of life data, in Mesbah M, Cole BF, Ting Lee M-L (eds): Statistical Methods for Quality of Life Studies: Design, Measurements and Analysis. Kluwer Academic Publishers 2002). The QOLIXANE study is a prospective, noninterventional, multicenter substudy of the Platform for Outcome, Quality of Life and Translational Research on Pancreatic Cancer (PARAGON) registry, which evaluated QoL in patients with mPC receiving first-line gemcitabine and nab-paclitaxel chemotherapy in real-life setting. QoL was prospectively measured via EORTC QLQ-C30 questionnaires at baseline and every month thereafter. Therapy and efficacy parameters were prospectively collected. Main objectives were the rate of patients without deterioration of Global Health Status/QoL (GHS/QoL) at 3 and 6 months. Six hundred patients were enrolled in 95 German study sites. Median progression-free survival was 5.9 months (95% confidence interval [CI], 5.2-6.3). Median overall survival (OS) was 8.9 months (95% CI, 7.9-10.2), while median time to deterioration of GHS/QoL was 4.7 months (95% CI, 4.0-5.6). With a baseline GHS/QoL score of 46 (SD, 22.8), baseline QoL of the patients was severely impaired, in most cases due to loss in role functioning and fatigue. In the Kaplan-Meier analysis, 61% and 41% of patients had maintained GHS/QoL after 3 and 6 months, respectively. However, in the QoL response analysis, 35% and 19% of patients had maintained (improved or stable) GHS/QoL after 3 and 6 months, respectively, while 14% and 9% had deteriorated GHS/QoL with the remaining patients being nonevaluable. In the Cox regression analysis, GHS/QoL scores strongly predicted survival with a hazard ratio of 0.86 (P < .0001). Patients with mPC have poor QoL at baseline that deteriorates within a median of 4.7 months. Treatment with gemcitabine and nab-paclitaxel is associated with maintained QoL in relevant proportions of patients. However, overall, results remain poor, reflecting the aggressive nature of the disease.

Real-life results from the prospective QoliXane trial of the platform for outcome, quality of life, and translational research on pancreatic cancer (PARAGON) registry

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Background: Gemcitabine and nab-paclitaxel (NPG) is standard first-line therapy for metastatic pancreatic cancer (mPC), but the pivotal study did not include quality of life (QoL) analyses. Methods: The QOLIXANE-PARAGON study started as a prospective, non-interventional, multicenter study conducted in Germany and transitioned into a permanent registry for pancreatic cancer patients (pts) considering all types of treatments. This report focuses on the pts enrolled into the QOLIXANE portion of the study. Pts were recruited from 95 German centers. QoL was prospectively measured via EORTC-C30 questionnaires (prior to and every month thereafter): therapy and efficacy parameters were prospectively collected. QoL and efficacy endpoints were analyzed in the intention-to-treat population (ITT). The primary endpoint was the rate of pts without deterioration of QoL/Global Health Score (QoL/GHS) at 3 months. Results: 600 pts were enrolled. Mean GHS/QoL score at baseline was low and was 46.2 (SD 22.8). Median progression-free survival was 5.85 months (95% CI, 5.23 to 6.25). Median overall survival (OS) was 8.91 months (95% CI, 7.89 to 10.19). The KM-analysis showed that 61% and 41% of pts had maintained QoL/GHS after 3 and 6 months, respectively. Median time to deterioration of QoL/GHS was 4.68 months (95% CI, 4.04 to 5.59). Mean QoL/GHS improved from 46.1 (SD 22.7) at baseline to 52.8 (SD 21.3) after 6 months. In the QoL response analysis, 34.6%, 37.4% and 28% of evaluable pts had improved, stable and worse QoL/GHS after 3 months, respectively. In the Cox regression analysis, GHS/QoL scores strongly predicted survival with a HR of 0.86 (p < 0.0001). Conclusions: QoliXane the largest study on QoL of mPC. It shows that time to deterioration of QoL is short but that a relevant group of mPC in first line have improved or maintained QoL after 3 and 6 months and that QoL is a predictor of pts outcome. Clinical trial information: NCT02691052 .

Perioperative chemotherapy with fluorouracil plus leucovorin, oxaliplatin, and docetaxel versus fluorouracil or capecitabine plus cisplatin and epirubicin for locally advanced, resectable gastric or gastro-oesophageal junction adenocarcinoma (FLOT4): a randomised, phase 2/3 trial

BACKGROUND

Docetaxel-based chemotherapy is effective in metastatic gastric and gastro-oesophageal junction adenocarcinoma. This study reports on the safety and efficacy of the docetaxel-based triplet FLOT (fluorouracil plus leucovorin, oxaliplatin and docetaxel) as a perioperative therapy for patients with locally advanced, resectable tumours.

METHODS

In this controlled, open-label, phase 2/3 trial, we randomly assigned 716 patients with histologically-confirmed advanced clinical stage cT2 or higher or nodal positive stage (cN+), or both, resectable tumours, with no evidence of distant metastases, via central interactive web-based-response system, to receive either three pre-operative and three postoperative 3-week cycles of 50 mg/m² epirubicin and 60 mg/m² cisplatin on day 1 plus either 200 mg/m² fluorouracil as continuous intravenous infusion or 1250 mg/m² capecitabine orally on days 1 to 21 (ECF/ECX; control group) or four preoperative and four postoperative 2-week cycles of 50 mg/m² docetaxel, 85 mg/m² oxaliplatin, 200 mg/m² leucovorin and 2600 mg/m² fluorouracil as 24-h infusion on day 1 (FLOT; experimental group). The primary outcome of the trial was overall survival (superiority) analysed in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, number NCT01216644.

FINDINGS

Between Aug 8, 2010, and Feb 10, 2015, 716 patients were randomly assigned to treatment in 38 German hospitals or with practice-based oncologists. 360 patients were assigned to ECF/ECX and 356 patients to FLOT. Overall survival was increased in the FLOT group compared with the ECF/ECX group (hazard ratio [HR] 0·77; 95% confidence interval [CI; 0.63 to 0·94]; median overall survival, 50 months [38·33 to not reached] vs 35 months [27·35 to 46·26]). The number of patients with related serious adverse events (including those occurring during hospital stay for surgery) was similar in the two groups (96 [27%] in the ECF/ECX group vs 97 [27%] in the FLOT group), as was the number of toxic deaths (two [<1%] in both groups). Hospitalisation for toxicity occurred in 94 patients (26%) in the ECF/ECX group and 89 patients (25%) in the FLOT group.

INTERPRETATION

In locally advanced, resectable gastric or gastro-oesophageal junction adenocarcinoma, perioperative FLOT improved overall survival compared with perioperative ECF/ECX.

FUNDING

The German Cancer Aid (Deutsche Krebshilfe), Sanofi-Aventis, Chugai, and Stiftung Leben mit Krebs Foundation.

CabaGast: multicentre, Phase II study with cabazitaxel in previously treated patients with advanced or metastatic adenocarcinoma of the esophagogastric junction and stomach

INTRODUCTION

This is a single-arm study (NCT01956149) to determine the prolonged (≥ 4 months) disease control rate with cabazitaxel administered in second-(or later) setting for patients with advanced or metastatic adenocarcinoma of the esophagogastric junction (EGJ) and stomach.

METHODS

65 patients with advanced EGJ and stomach cancer were treated with 20 mg/m² cabazitaxel every 3 weeks for a maximum of six cycles. The main objective of the study is a prolonged disease control rate (pDCR: CR, PR or SD lasting at least 4 months). Secondary outcome measures were overall survival, progression-free survival, response rate by subgroup (with vs without previous treatment with a taxane) and toxicity. Patients were assessed for tumor response every 6 weeks during therapy and during the follow-up (up to 12 months).

RESULTS

65 patients (median age: 63, range 31-86 years) were assigned to treatment. Median no. of prior therapies that had received prior taxane therapy was 2. 80%. Patients received a median of two cycles of cabazitaxel. Efficacy results are for the ITT population. The mDCR in n = 65 patients was 10.8% (95% CI 4.4-20.9%). There was a control of disease (CR + PR + SD) in n = 26 patients of n = 65, corresponding to a DCR of 40.0% (95% CI 28.0-52.9%). In patients without prior taxane use, it was 46.2% (95% CI 25.1-80.8%) and in patients with only one prior therapy, DCR was 50.0% (95% CI 31.3-68.7%). The median overall survival was 4.6 months (95% CI 3.16, 5.59) in the whole ITT population. In patients with only one prior therapy, median OS was 5.4 months (95% CI 2.60, 7.43) and in patients without taxane pretreatment, it was 6.4 months (95% CI 1.38, 14.17). The median progression-free survival time was 1.5 months (95% CI 1.32, 2.27) in the whole ITT population, 2.9 months (95% CI 0.72, 4.67) without prior taxane therapy and was 1.7 (95% CI 1.28, 3.35) months in patients with only one prior therapy median.

CONCLUSIONS

Cabazitaxel is active in heavily pretreated patients with metastatic and advanced esophagogastric junction and gastric adenocarcinoma. Efficacy results in a classic second-line population are comparable to other second-line studies, therefore, under the limitations of this trial, (single arm, Phase II design) cabazitaxel might be an option especially in patients without prior taxane therapy, in second line and even further line therapy of metastatic and advanced esophagogastric junction and gastric adenocarcinoma.

A multicentre, phase II study with cabazitaxel in previously treated patients with advanced or metastatic adenocarcinoma of the oesophagogastric junction and stomach (CABAGAST)

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Background: This is a single-arm study to determine prolonged ( > = 4 months) disease control rate with cabazitaxel administered in second- (or later) setting for patients with advanced or metastatic adenocarcinoma of the esophagogastric junction (EGJ) and stomach. Methods: 65 patients with advanced EGJ and stomach cancer were treated with 20mg/m2 Cabazitaxel every 3 weeks for a maximum of 6 cycles. Main objective of the study was a prolonged Disease Control Rate (pDCR: CR, PR or SD lasting at least 4 months). Secondary Outcome Measures were overall survival (OS), progression-free survival (PFS), response rate by subgroup (with vs without previous treatment with a taxane) and toxicity. Patients were assessed for tumor response every 6 weeks during therapy and during follow-up (up to 12 months). Results: 65 patients (median age: 63, range 31-86 years) were assigned. Median no. of prior therapies was 2. 80% had received prior taxane therapy. Patients received a median of 2 cycles of cabazitaxel. Efficacy results are shown for the per protocol (PP) population. pDCR rate was 12.7%, (95%CI: 5,3%- 24.5%). pDCR was 20.0% in 2nd line patients (95%CI: 6.8%-40.7%) and 30.0% (95%CI: 6.7%-65.2%) in all lines in patients without prior taxane use. Response Rate was 5.5% (95%CI: 1.1%-15.1%) in total PP and 20.0% in the population without prior taxane use. Median OS was 4.6 months (7.4 months without prior taxane vs 3.8 months with prior taxane). Median PFS was 1.38 months (95%CI: 1.28- 1.87) with and 2.01 months (95%CI: 0.20- 4.67) without prior taxane use. Most common grade 3/4 toxicities were neutropenia in 13% of the patients, pain (12%), leucopenia (10%), anemia (10%), fatigue (10%) and nausea (10%). Conclusions: Cabazitaxel is active in heavily pretreated patients with metastatic and advanced esophagogastric junction and gastric adenocarcinoma. Toxicity is moderate. Patients without prior taxane use derived more benefit from Cabazitaxel. Clinical trial information: NCT01956149.

[Verruciform xanthoma]

BACKGROUND

Verruciform xanthoma (VX), a rare, benign lesion of the skin and mucosa, is slow-growing, asymptomatic and characterized by a granular (verruciform) surface. It is yellowish-red or grey in color and up to 2 cm in diameter. Histologically, a papillary and/or verrucous proliferation of the squamous epithelium with hyperparakeratosis and numerous foam cells is present. These cells are predominantly located within the papillae of the lamina propria. For differential diagnosis, other papillomatous and verrucous lesions such as verrucous carcinomas or squamous cell carcinomas need to be ruled out.

CASE REPORT

A 46-year-old patient with VX located on the alveolar process regio 26-28 is presented. Clinically, a 2 x 2 cm granular, oral mucosa surface lesion extending onto the palate occurred in regio 26-28. Biopsy was characterized light microscopically by the presence of swollen, elongated cells in the submucosa, an indication of VX alterations. Transmission electron microscopy demonstrated foam cells in the subepithelium containing numerous membrane-bound vesicles similar in diameter and showing a wide variation in electron density. Morphologically, these cells resembled macrophage-related cells. The lesion was excised in total with no evidence of recurrence after 9 months.

DISCUSSION

The pathogenesis of VX is still unclear. The characteristic xanthoma cells may play a major role in VX. Microscopic analysis of the morphology of the foam cells indicated that they may represent a differentiated form of macrophages. Lipid vesicles inside these cells differed in their electron density indicating a heterogeneous biochemistry or different states of maturation.

Sustained depolarisation induces changes in the extracellular concentrations of purine and pyrimidine nucleosides in the rat thalamus

ATP and adenosine are well-known neuroactive compounds. Other nucleotides and nucleosides may also be involved in different brain functions. This paper reports on extracellular concentrations of nucleobases and nucleosides (uracil, hypoxanthine, xanthine, uridine, 2'-deoxycytidine, 2'-deoxyuridine, inosine, guanosine, thymidine, adenosine) in response to sustained depolarisation, using in vivo brain microdialysis technique in the rat thalamus. High-potassium solution, the glutamate agonist kainate, and the Na(+)/K(+) ATPase blocker ouabain were applied in the perfusate of microdialysis probes and induced release of various purine and pyrimidine nucleosides. All three types of depolarisation increased the level of hypoxanthine, uridine, inosine, guanosine and adenosine. The levels of measured deoxynucleosides (2'-deoxycytidine, 2'-deoxyuridine and thymidine) decreased or did not change, depending on the type of depolarisation. Kainate-induced changes were TTX insensitive, and ouabain-induced changes for inosine, guanosine, 2'-deoxycytidine and 2'-deoxyuridine were TTX sensitive. In contrast, TTX application without depolarisation decreased the extracellular concentrations of hypoxanthine, uridine, inosine, guanosine and adenosine. Our data suggest that various nucleosides may be released from cells exposed to excessive activity and, thus, support several different lines of research concerning the regulatory roles of nucleosides.

Analysis of purine and pyrimidine bases, nucleosides and deoxynucleosides in brain microsamples (microdialysates and micropunches) and cerebrospinal fluid

A new chromatographic method is reported for the synchronous analysis of endogenous purine and pyrimidine bases, ribonucleosides, and deoxyribonucleosides in brain samples. An optimized gradient chromatography system with a cooled reversed-phase column allows the detection of these compounds in very low concentrations in microsamples (microdialysates and micropunches). Chromatographic peaks were identified via the retention times of known standards, with detection at two wavelengths, and also by electrospray tandem mass spectrometry, which permits the identification of certain compounds at extremely low concentrations. The method was tested on in vivo brain microdialysis samples, micropunch tissue sample and cerebrospinal fluid of rats. Extracellular concentrations of pyrimidine metabolites in brain samples and of various purine metabolites in thalamic samples are reported here first. A comparison of the results on microdialysis and cerebrospinal fluid samples suggests that the analysis of cerebrospinal fluid provides limited information on the local extracellular concentrations of these compounds. Basic dialysis experiments revealed temporarily stable baseline levels one hour after implantation of the microdialysis probes. An elevated potassium concentration in the perfusion solution caused increases in the extracellular levels of adenosine and its metabolites, and of guanosine and the pyrimidine nucleoside uridine.