First-line systemic treatment strategies in patients with initially unresectable colorectal cancer liver metastases (CAIRO5): an open-label, multicentre, randomised, controlled, phase 3 study from the Dutch Colorectal Cancer Group.

BACKGROUND: Patients with initially unresectable colorectal cancer liver metastases might qualify for local treatment with curative intent after reducing the tumour size by induction systemic treatment. We aimed to compare the currently most active induction regimens. METHODS: In this open-label, multicentre, randomised, phase 3 study (CAIRO5), patients aged 18 years or older with histologically confirmed colorectal cancer, known RAS/BRAFV600E mutation status, WHO performance status of 0-1, and initially unresectable colorectal cancer liver metastases were enrolled at 46 Dutch and one Belgian secondary and tertiary centres. Resectability or unresectability of colorectal cancer liver metastases was assessed centrally by an expert panel of liver surgeons and radiologists, at baseline and every 2 months thereafter by predefined criteria. Randomisation was done centrally with the minimisation technique via a masked web-based allocation procedure. Patients with right-sided primary tumour site or RAS or BRAFV600E mutated tumours were randomly assigned (1:1) to receive FOLFOX or FOLFIRI plus bevacizumab (group A) or FOLFOXIRI plus bevacizumab (group B). Patients with left-sided and RAS and BRAFV600E wild-type tumours were randomly assigned (1:1) to receive FOLFOX or FOLFIRI plus bevacizumab (group C) or FOLFOX or FOLFIRI plus panitumumab (group D), every 14 days for up to 12 cycles. Patients were stratified by resectability of colorectal cancer liver metastases, serum lactate dehydrogenase concentration, choice of irinotecan versus oxaliplatin, and BRAFV600E mutation status (for groups A and B). Bevacizumab was administered intravenously at 5 mg/kg. Panitumumab was administered intravenously at 6 mg/kg. FOLFIRI consisted of intravenous infusion of irinotecan at 180 mg/m2 with folinic acid at 400 mg/m2, followed by bolus fluorouracil at 400 mg/m2 intravenously, followed by continuous infusion of fluorouracil at 2400 mg/m2. FOLFOX consisted of oxaliplatin at 85 mg/m2 intravenously together with the same schedule of folinic acid and fluorouracil as in FOLFIRI. FOLFOXIRI consisted of irinotecan at 165 mg/m2 intravenously, followed by intravenous infusion of oxaliplatin at 85 mg/m2 with folinic acid at 400 mg/m2, followed by continuous infusion of fluorouracil at 3200 mg/m2. Patients and investigators were not masked to treatment allocation. The primary outcome was progression-free survival, analysed on a modified intention-to-treat basis, excluding patients who withdrew consent before starting study treatment or violated major entry criteria (no metastatic colorectal cancer, or previous liver surgery for colorectal cancer liver metastases). The study is registered with ClinicalTrials.gov, NCT02162563, and accrual is complete. FINDINGS: Between Nov 13, 2014, and Jan 31, 2022, 530 patients (327 [62%] male and 203 [38%] female; median age 62 years [IQR 54-69]) were randomly assigned: 148 (28%) patients to group A, 146 (28%) patients to group B, 118 (22%) patients to group C, and 118 (22%) patients to group D. Groups C and D were prematurely closed for futility. 521 patients were included in the modified intention-to-treat population (147 in group A, 144 in group B, 114 in group C, and 116 in group D). The median follow-up at the time of this analysis was 51·1 months (95% CI 47·7-53·1) in groups A and B and 49·9 months (44·5-52·5) in in groups C and D. Median progression-free survival was 9·0 months (95% CI 7·7-10·5) in group A versus 10·6 months (9·9-12·1) in group B (stratified hazard ratio [HR] 0·76 [95% CI 0·60-0·98]; p=0·032), and 10·8 months (95% CI 9·9-12·6) in group C versus 10·4 months (9·8-13·0) in group D (stratified HR 1·11 [95% CI 0·84-1·48]; p=0·46). The most frequent grade 3-4 events in groups A and B were neutropenia (19 [13%] patients in group A vs 57 [40%] in group B; p<0·0001), hypertension (21 [14%] vs 20 [14%]; p=1·00), and diarrhoea (five [3%] vs 28 [19%]; p<0·0001), and in groups C and D were neutropenia (29 [25%] vs 24 [21%]; p=0·44), skin toxicity (one [1%] vs 29 [25%]; p<0·0001), hypertension (20 [18%] vs eight [7%]; p=0·016), and diarrhoea (five [4%] vs 18 [16%]; p=0·0072). Serious adverse events occurred in 46 (31%) patients in group A, 75 (52%) patients in group B, 41 (36%) patients in group C, and 49 (42%) patients in group D. Seven treatment-related deaths were reported in group B (two due to multiorgan failure, and one each due to sepsis, pneumonia, portal vein thrombosis, septic shock and liver failure, and sudden death), one in group C (multiorgan failure), and three in group D (cardiac arrest, pulmonary embolism, and abdominal sepsis). INTERPRETATION: In patients with initially unresectable colorectal cancer liver metastases, FOLFOXIRI-bevacizumab was the preferred treatment in patients with a right-sided or RAS or BRAFV600E mutated primary tumour. In patients with a left-sided and RAS and BRAFV600E wild-type tumour, the addition of panitumumab to FOLFOX or FOLFIRI showed no clinical benefit over bevacizumab, but was associated with more toxicity. FUNDING: Roche and Amgen.

Olaparib Efficacy in Patients with Metastatic Castration-resistant Prostate Cancer and BRCA1, BRCA2, or ATM Alterations Identified by Testing Circulating Tumor DNA.

PURPOSE: The phase III PROfound study (NCT02987543) evaluated olaparib versus abiraterone or enzalutamide (control) in metastatic castration-resistant prostate cancer (mCRPC) with tumor homologous recombination repair (HRR) gene alterations. We present exploratory analyses on the use of circulating tumor DNA (ctDNA) testing as an additional method to identify patients with mCRPC with HRR gene alterations who may be eligible for olaparib treatment. PATIENTS AND METHODS: Plasma samples collected during screening in PROfound were retrospectively sequenced using the FoundationOne®Liquid CDx test for BRCA1, BRCA2 (BRCA), and ATM alterations in ctDNA. Only patients from Cohort A (BRCA/ATM alteration positive by tissue testing) were evaluated. We compared clinical outcomes, including radiographic progression-free survival (rPFS) between the ctDNA subgroup and Cohort A. RESULTS: Of the 181 (73.9%) Cohort A patients who gave consent for plasma sample ctDNA testing, 139 (76.8%) yielded a result and BRCA/ATM alterations were identified in 111 (79.9%). Of these, 73 patients received olaparib and 38 received control. Patients' baseline demographics and characteristics, and the prevalence of HRR alterations were comparable with the Cohort A intention-to-treat (ITT) population. rPFS was longer in the olaparib group versus control [median 7.4 vs. 3.5 months; hazard ratio (HR), 0.33; 95% confidence interval (CI), 0.21-0.53; nominal P < 0.0001], which is consistent with Cohort A ITT population (HR, 0.34; 95% CI, 0.25-0.47). CONCLUSIONS: When tumor tissue testing is not feasible or has failed, ctDNA testing may be a suitable alternative to identify patients with mCRPC carrying BRCA/ATM alterations who may benefit from olaparib treatment.

Olaparib tolerability and common adverse-event management in patients with metastatic castration-resistant prostate cancer: Further analyses from the PROfound study.

BACKGROUND: Based on PROfound, olaparib is approved for patients with metastatic castration-resistant prostate cancer following disease progression on at least enzalutamide or abiraterone and who carry relevant alterations in DNA repair genes. To facilitate continued olaparib treatment as long as the patient derives benefit, we describe further safety assessments from PROfound focusing on the four most common adverse events (AEs) and events of special interest. METHODS: Patients were randomized (2:1) to olaparib tablets (300 mg bid) or control (enzalutamide or abiraterone) until disease progression or unacceptable toxicity. Safety was assessed through AE reporting and laboratory assessments. Safety data were also collected from all patients in the control group who experienced radiographic disease progression and subsequently crossed over to olaparib treatment. RESULTS: 256 patients received olaparib and 130 control. Incidence rates for the four most commonly occurring AEs in the olaparib group (all-causality) were anaemia 50%, nausea 43%, fatigue/asthenia 42% and decreased appetite 31%. All were mostly Grade 1 and 2 and all peaked within the first 2 months of treatment as the events were managed where appropriate, primarily with dose interruptions or dose reductions. The extent of bone metastases at baseline or prior taxane use was not associated with the rate of anaemia. Pneumonitis was reported in 2% and 1.5% of patients in the olaparib and control groups, respectively, and one patient (0.4%) in the olaparib group experienced an event of MDS/AML after a 30-day follow-up period. Venous thromboembolic events occurred in 8% of olaparib and 3% of control patients. CONCLUSIONS: The four most common AEs observed in PROfound were generally manageable without the need for treatment discontinuation, allowing patients to remain on treatment for as long as they were deriving clinical benefit. CLINICALTRIALS: gov registration number: NCT02987543.

Therapeutic Drug Monitoring of Endoxifen for Tamoxifen Precision Dosing: Feasible in Patients with Hormone-Sensitive Breast Cancer.

BACKGROUND: Endoxifen is the most important active metabolite of tamoxifen. Several retrospective studies have suggested a minimal or threshold endoxifen systemic concentration of 14-16 nM is required for a lower recurrence rate. The aim of this study was to investigate the feasibility of reaching a predefined endoxifen level of ≥ 16 nM (5.97 ng/mL) over time using therapeutic drug monitoring (TDM). METHODS: This prospective open-label intervention study enrolled patients who started treatment with a standard dose of tamoxifen 20 mg once daily for early breast cancer. An outpatient visit was combined with a TDM sample at 3, 4.5, and 6 months after initiation of the tamoxifen treatment. The tamoxifen dose was escalated to a maximum of 40 mg if patients had an endoxifen concentration < 16 nM. The primary endpoint of the study was the percentage of patients with an endoxifen level ≥ 16 nM at 6 months after the start of therapy compared with historical data, in other words, 80% of patients with endoxifen levels ≥ 16 nM with standard therapy. RESULTS: In total, 145 patients were included. After 6 months, 89% of the patients had endoxifen levels ≥ 16 nM, compared with a literature-based 80% of patients with endoxifen levels ≥ 16 nM at baseline (95% confidence interval 82-94; P = 0.007). In patients with an affected CYP2D6 allele, it was not always feasible to reach the predefined endoxifen level of ≥ 16 nM. No increase in tamoxifen-related adverse events was reported after dose escalation. CONCLUSION: This study demonstrated that it is feasible to increase the percentage of patients with endoxifen levels ≥ 16 nM using TDM. TDM is a safe strategy that offers the possibility of nearly halving the number of patients with endoxifen levels < 16 nM.

Carboplatin-Cyclophosphamide or Paclitaxel without or with Bevacizumab as First-Line Treatment for Metastatic Triple-Negative Breast Cancer (BOOG 2013-01).

BACKGROUND: The addition of bevacizumab to chemotherapy conferred a modest progression-free survival (PFS) benefit in metastatic triple-negative breast cancer (mTNBC). However, no overall survival (OS) benefit has been reported. Also, its combination with carboplatin-cyclophosphamide (CC) has never been investigated. METHODS: The Triple-B study is a multicenter, randomized phase IIb trial that aims to prospectively validate predictive biomarkers, including baseline plasma vascular endothelial growth factor receptor-2 (pVEGFR-2), for bevacizumab benefit. mTNBC patients were randomized between CC and paclitaxel (P) without or with bevacizumab (CC ± B or P ± B). Here we report on a preplanned safety and preliminary efficacy analysis after the first 12 patients had been treated with CC+B and on the predictive value of pVEGFR-2. RESULTS: In 58 patients, the median follow-up was 22.1 months. Toxicity was manageable and consistent with what was known for each agent separately. There was a trend toward a prolonged PFS with bevacizumab compared to chemotherapy only (7.0 vs. 5.2 months; adjusted HR = 0.60; 95% CI 0.33-1.08; p = 0.09), but there was no effect on OS. In this small study, pVEGFR-2 concentration did not predict a bevacizumab PFS benefit. Both the intention-to-treat analysis and the per-protocol analysis did not yield a significant treatment-by-biomarker test for interaction (pinteraction = 0.69). CONCLUSIONS: CC and CC+B are safe first-line regimens for mTNBC and the side effects are consistent with those known for each individual agent. pVEGFR-2 concentration did not predict a bevacizumab PFS benefit.

The Risk of QTc-Interval Prolongation in Breast Cancer Patients Treated with Tamoxifen in Combination with Serotonin Reuptake Inhibitors.

PURPOSE: Antidepressants like the serotonin reuptake inhibitors (SRIs) are often used concomitantly with tamoxifen (e.g. for treatment of depression). This may lead to an additional prolongation of the QTc-interval, with an increased risk of cardiac side effects. Therefore we investigated whether there is a drug-drug interaction between tamoxifen and SRIs resulting in a prolonged QTc-interval. METHODS: Electrocardiograms (ECGs) of 100 patients were collected at steady state tamoxifen treatment, with or without concomitant SRI co-medication. QTc-interval was manually measured and calculated using the Fridericia formula. Primary outcome was difference in QTc-interval between tamoxifen monotherapy and tamoxifen concomitantly with an SRI. RESULTS: The mean QTc-interval was 12.4 ms longer when tamoxifen was given concomitantly with an SRI (95% CI:1.8-23.1 ms; P = 0.023). Prolongation of the QTc-interval was particularly pronounced for paroxetine (17.2 ms; 95%CI:1.4-33.0 ms; P = 0.04), escitalopram (12.5 ms; 95%CI:4.4-20.6 ms; P < 0.01) and citalopram (20.7 ms; 95%CI:0.7-40.7 ms; P = 0.047), where other agents like venlafaxine did not seem to prolong the QTc-interval. None of the patients had a QTc-interval of >500 ms. CONCLUSIONS: Concomitant use of tamoxifen and SRIs resulted in a significantly higher mean QTc-interval, which was especially the case for paroxetine, escitalopram and citalopram. When concomitant administration with an SRI is warranted venlafaxine is preferred.

Impact of Curcumin (with or without Piperine) on the Pharmacokinetics of Tamoxifen.

Tamoxifen is a prodrug that is primarily metabolized into the pharmacologically active metabolite endoxifen and eventually into inactive metabolites. The herb curcumin may increase endoxifen exposure by affecting phase II metabolism. We compared endoxifen and tamoxifen exposure in breast cancer patients with or without curcumin, and with addition of the bio-enhancer piperine. Tamoxifen (20⁻30mg per day (q.d.)) was either given alone, or combined with curcumin (1200 mg three times daily (t.i.d.)) +/- piperine (10 mg t.i.d.). The primary endpoint of this study was the difference in geometric means for the area under the curve (AUC) of endoxifen. Genotyping was performed to determine CYP2D6 and CYP3A4 phenotypes. The endoxifen AUC0⁻24h decreased with 7.7% (95%CI: -15.4 to 0.7%; p = 0.07) with curcumin and 12.4% (95%CI: -21.9 to -1.9%; p = 0.02) with curcumin and piperine, compared to tamoxifen alone. Tamoxifen AUC0⁻24h showed similar results. For patients with an extensive CYP2D6 metabolism phenotype (EM), effects were more pronounced than for intermediate CYP2D6 metabolizers (IMs). In conclusion, the exposure to tamoxifen and endoxifen was significantly decreased by concomitant use of curcumin (+/- piperine). Therefore, co-treatment with curcumin could lower endoxifen concentrations below the threshold for efficacy (potentially 20⁻40% of the patients), especially in EM patients.

Effects of prednisone on docetaxel pharmacokinetics in men with metastatic prostate cancer: A randomized drug-drug interaction study.

AIMS: Docetaxel has been approved for the treatment of metastatic prostate cancer in combination with prednisone. Since prednisone is known to induce the cytochrome P450 iso-enzyme CYP3A4, which is the main metabolizing enzyme of docetaxel in the liver, a potential drug-drug interaction may occur. In this prospective randomized pharmacokinetic cross-over study we investigated docetaxel exposure with concomitant prednisone, compared to docetaxel monotherapy in men with metastatic prostate cancer. METHODS: Patients scheduled to receive at least 6 cycles of docetaxel (75 mg/m2 ) and who gave written informed consent were randomized to receive either the 1st 3 cycles, or the last 3 consecutive cycles with prednisone (twice daily 5 mg). Pharmacokinetic blood sampling was performed during cycle 3 and cycle 6. Primary endpoint was difference in docetaxel exposure, calculated as area under the curve (AUC0-inf ) and analysed by means of a linear mixed model. Given the cross-over design the study was powered on 18 patients to answer the primary, pharmacokinetic, endpoint. RESULTS: Eighteen evaluable patients were included in the trial. Docetaxel concentration with concomitant prednisone (AUC0-inf 2784 ng*h/mL, 95% confidence interval 2436-3183 ng*h/mL) was similar to the concentration of docetaxel monotherapy (AUC0-inf 2647 ng*h/mL, 95% confidence interval 2377-2949 ng*h/mL). Exploratory analysis showed no toxicity differences between docetaxel monotherapy and docetaxel cycles with prednisone. CONCLUSION: No significant difference in docetaxel concentrations was observed. In addition, we found similar toxicity profiles in absence and presence of prednisone. Therefore, from a pharmacokinetic point of view, docetaxel may be administrated with or without prednisone.

SWITCH II: Phase III randomized, sequential, open-label study to evaluate the efficacy and safety of sorafenib-pazopanib versus pazopanib-sorafenib in the treatment of advanced or metastatic renal cell carcinoma (AUO AN 33/11).

PURPOSE: This trial compared the sequential therapy with the multikinase inhibitor sorafenib (So) followed by pazopanib (Pa) or vice versa in advanced/metastatic renal cell carcinoma (mRCC) patients. METHODS: This multicenter, randomized phase 3 study assessed the sequential use of So-Pa versus Pa-So in patients with mRCC without prior systemic therapy. Pts were randomized to So 2 × 400 mg/day followed by Pa 1 × 800 mg/day in case of progression or intolerable toxicity or vice versa. Primary endpoint was total PFS (tPFS), defined as time from randomization to progression, or death during second-line therapy. Key secondary endpoints included overall survival (OS), first-line PFS, disease control rate (DCR) and safety. RESULTS: A total of 377 pts were randomized (So-Pa, n = 189; Pa-So, n = 188). Recruitment of a total 544 pts was calculated, but actual accrual rate turned out to be lower than expected. The primary endpoint median tPFS was 8.6 mo (95% CI 7.7-10.2) for So-Pa and 12.9 mo (95% CI 10.8-15.2) for Pa-So with a hazard ratio (HR) of 1.36 (upper limit of one-sided 95% CI 1.68), which exceeded a predefined HR <1.225 as a one-sided 95% confidence interval. Non-inferiority of So-Pa regarding tPFS was not met. Secondary endpoints displayed marked statistical differences in favor of Pa-So in first-line PFS and DCR but not for OS and 2nd-line PFS. Side effect profiles were consistent with known toxicities of the respective multikinase-inhibitor including diarrhea, fatigue, hand-foot skin reaction and hypertension. CONCLUSIONS: Non-inferiority of the primary endpoint tPFS could not be demonstrated for So-Pa. The results for first-line PFS and DCR favored the Pa-So sequence. TRIAL REGISTRATION: NCT01613846, www.clinicaltrials.gov.

Prognostic factors in men with metastatic castration-resistant prostate cancer treated with cabazitaxel.

BACKGROUND: Treatment selection for men with metastatic castration-resistant prostate cancer (mCRPC) has become increasingly challenging with the introduction of novel therapies at earlier disease stages. The purpose of this study was to identify prognostic factors for overall survival (OS) and PSA response in patients with mCRPC treated with cabazitaxel. RESULTS: 224 mCRPC patients were included in the current analysis. In multivariable analysis, WHO performance status, baseline hemoglobin, alkaline phosphatase and albumin were all significantly associated with OS. Hemoglobin and alkaline phosphatase were significantly associated with PSA response. CONCLUSIONS: This study identified prognostic factors for OS and PSA response of men with mCRPC treated with cabazitaxel. In an increasingly complicated treatment landscape with several treatment options available our findings might serve to estimate the chance of survival of men qualifying for treatment with second-line chemotherapy in daily practice. Furthermore, these data can be used to risk-stratify patients in clinical trials. METHODS: We performed a post-hoc analysis of a randomized phase II trial of mCRPC patients treated with cabazitaxel. Cox and logistic regression models were used to investigate the influence of clinical and biochemical variables on OS and PSA response. Nomograms were developed to estimate the chance of PSA response and OS.

Effects of Budesonide on Cabazitaxel Pharmacokinetics and Cabazitaxel-Induced Diarrhea: A Randomized, Open-Label Multicenter Phase II Study.

Purpose: Forty-seven percent of patients in the pivotal trial of cabazitaxel reported diarrhea of any grade. Aiming to reduce the incidence of diarrhea, we studied the effects of budesonide on the grade of cabazitaxel-induced diarrhea during the first two treatment cycles.Experimental Design: Between December 2011 and October 2015, 246 metastatic castration-resistant prostate cancer patients were randomized to receive standard-of-care cabazitaxel 25 mg/m2 every 3 weeks plus prednisone 10 mg/day (group CABA) or same dose/schedule of cabazitaxel with concomitant budesonide 9 mg daily during the first two treatment cycles (group BUD). The occurrence of diarrhea was reported by physicians and by patients in a diary. χ2 tests were used to compare incidence numbers. An intention-to-treat principle was used.Results: In the phase II trial, 227 patients were evaluable. Grade 2-3 diarrhea occurred in 35 patients (15%) and grade 4 diarrhea was not reported. The incidence of grade 2-3 diarrhea was comparable in both treatment groups: 14 of 113 patients in group CABA (12%) versus 21 of 114 patients in group BUD (18%; P = 0.21). Seven patients were admitted to the hospital with diarrhea (n = 5 group CABA vs. n = 2 group BUD). PSA response was seen in 30% of patients and was not affected by budesonide coadministration (P = 0.29). Also, other toxicities were not affected by budesonide coadministration.Conclusions: The incidence of cabazitaxel-induced diarrhea was notably lower than reported in the TROPIC trial and appears manageable in routine clinical practice. Budesonide coadministration did not reduce the incidence or severity of cabazitaxel-induced diarrhea. Clin Cancer Res; 23(7); 1679-83. ©2016 AACR.

Augmentation of Endoxifen Exposure in Tamoxifen-Treated Women Following SSRI Switch.

BACKGROUND AND OBJECTIVE: The anti-oestrogen tamoxifen requires metabolic activation to endoxifen by cytochrome P450 (CYP) enzymes, predominantly CYP2D6. Potent CYP2D6-inhibiting antidepressants can seriously disrupt tamoxifen metabolism, probably influencing the efficacy of tamoxifen. For this reason, paroxetine and fluoxetine are recommended not to be used with tamoxifen in breast cancer patients. We investigated the effects of switching potent CYP2D6-inhibiting antidepressants to weak CYP2D6-inhibiting antidepressants on the plasma pharmacokinetics of tamoxifen. METHODS: Ten breast cancer patients who were treated with tamoxifen in combination with a potent CYP2D6-inhibiting antidepressant (paroxetine or fluoxetine) for at least 4 weeks were enrolled. Under close supervision by a psychiatrist, patients were switched to treatment with escitalopram or venlafaxine (weak CYP2D6-inhibiting antidepressants). Before and after the switch, pharmacokinetic blood sampling was performed over 24 h. Pharmacokinetic parameters were estimated using noncompartmental analysis. Adverse effects were recorded during the study. RESULTS: Endoxifen exposure was ~3-fold higher during escitalopram co-administration than during paroxetine or fluoxetine co-administration (median 387 nM·h [range 159-637 nM·h] versus 99.2 nM·h [range 70.0-210 nM·h]; P = 0.012; Wilcoxon signed-rank test). The ratio of endoxifen to N-desmethyltamoxifen and the ratio of 4-hydroxytamoxifen to tamoxifen increased by 3.3- and ~1.5-fold, reflecting increased CYP2D6 activity. Antidepressant switching did not result in psychiatric problems or antidepressant-related adverse effects. CONCLUSION: In this study, switching to the weak CYP2D6 inhibitor escitalopram was safe and feasible and resulted in clinically relevant rises in endoxifen concentrations. We therefore advise switching paroxetine and fluoxetine to escitalopram in patients using tamoxifen. However, switching should always be weighed in individual patients.

Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

The anti-estrogen tamoxifen is characterized by a large variability in response, partly due to pharmacokinetic differences. We examined circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients. Pharmacokinetic analysis was performed in mice, dosed at six different times (24-h period). Tissue samples were used for mRNA expression analysis of drug-metabolizing enzymes. In patients, a cross-over study was performed. During three 24-h periods, after tamoxifen dosing at 8 a.m., 1 p.m., and 8 p.m., for at least 4 weeks, blood samples were collected for pharmacokinetic measurements. Differences in tamoxifen pharmacokinetics between administration times were assessed. The mRNA expression of drug-metabolizing enzymes showed circadian variation in mouse tissues. Tamoxifen exposure seemed to be highest after administration at midnight. In humans, marginal differences were observed in pharmacokinetic parameters between morning and evening administration. Tamoxifen C(max )and area under the curve (AUC)0-8 h were 20 % higher (P < 0.001), and tamoxifen t(max) was shorter (2.1 vs. 8.1 h; P = 0.001), indicating variation in absorption. Systemic exposure (AUC0-24 h) to endoxifen was 15 % higher (P < 0.001) following morning administration. The results suggest that dosing time is of marginal influence on tamoxifen pharmacokinetics. Our study was not designed to detect potential changes in clinical outcome or toxicity, based on a difference in the time of administration. Circadian rhythm may be one of the many determinants of the interpatient and intrapatient pharmacokinetic variability of tamoxifen.

Dextromethorphan as a phenotyping test to predict endoxifen exposure in patients on tamoxifen treatment.

PURPOSE: Tamoxifen, a widely used agent for the prevention and treatment of breast cancer, is mainly metabolized by CYP2D6 and CYP3A to form its most abundant active metabolite, endoxifen. Interpatient variability in toxicity and efficacy of tamoxifen is substantial. Contradictory results on the value of CYP2D6 genotyping to reduce the variable efficacy have been reported. In this pharmacokinetic study, we investigated the value of dextromethorphan, a known probe drug for both CYP2D6 and CYP3A enzymatic activity, as a potential phenotyping probe for tamoxifen pharmacokinetics. METHODS: In this prospective study, 40 women using tamoxifen for invasive breast cancer received a single dose of dextromethorphan 2 hours after tamoxifen intake. Dextromethorphan, tamoxifen, and their respective metabolites were quantified. Exposure parameters of all compounds were estimated, log transformed, and subsequently correlated. RESULTS: A strong and highly significant correlation (r = -0.72; P < .001) was found between the exposures of dextromethorphan (0 to 6 hours) and endoxifen (0 to 24 hours). Also, the area under the plasma concentration-time curve of dextromethorphan (0 to 6 hours) and daily trough endoxifen concentration was strongly correlated (r = -0.70; P < .001). In a single patient using the potent CYP2D6 inhibitor paroxetine, the low endoxifen concentration was accurately predicted by dextromethorphan exposure. CONCLUSION: Dextromethorphan exposure after a single administration adequately predicted endoxifen exposure in individual patients with breast cancer taking tamoxifen. This test could contribute to the personalization and optimization of tamoxifen treatment, but it needs additional validation and simplification before being applicable in future dosing strategies.

Trial design for cancer (cell)-specific anticancer therapies.

The last decade has brought a totally new class of systemic anticancer treatment options, the so-called cancer (cell)-specific (CCS) anticancer agents. Until recently, this treatment modality has been referred to as 'targeted therapy' but as all existing systemic anticancer therapies have a clearly defined target, this seems to be a misnomer. Despite impressive results of several CCS drugs, the present set up of drug development is ill suited for CCSs due to the nature of the majority of these compounds. The authors focus on specific aspects of how to design early clinical trials with this new class of anticancer agents with focus on pharmacodynamic behaviour in relation to response, optimal dose and treatment duration.