Beyond Skin Rash: Alpelisib-Induced Anaphylactic Reactions.

Alpelisib is a specific oral PI3K inhibitor used combined with fulvestrant for the treatment of patients with HR+/HER2-/PIK3CA-mutated metastatic breast cancer. Adverse drug reactions with alpelisib are common, including hyperglycemia and rash. Here we describe extraordinary and life-threatening reactions beyond skin rash in two patients with progressive PIK3CA-mutated metastatic cancer in whom alpelisib was initiated. Case-A (vaginal cancer): After 10 days on treatment, she developed dry eyes, generalized rash and itching. Alpelisib was interrupted and symptomatic treatment initiated. Because of an initial tumor response, a rechallenge was done. Ninety minutes after a reduced dose of alpelisib, she developed an anaphylactic reaction with angioedema, hypotension, and skin rash. Case-B (breast cancer): After 11 days on treatment, she developed skin rash and alpelisib was interrupted. At re-initiation, she felt tingles in her face and ears and some skin erythema. Given the mild rash, a second rechallenge with premedication was performed. Ninety minutes after a reduced dose of alpelisib, she developed a type-1 allergic reaction with angioedema, tingles, and skin rash. In both cases, a type-1 allergic reaction was diagnosed and symptomatic treatment was initiated, alpelisib was permanently discontinued and the patients fully recovered the next week(s). This report underlines the critical importance to consider type-I allergic reactions in the differential diagnosis in cases of rash associated with alpelisib. Even if a reaction develops after days on treatment, a type-I allergic reaction cannot be excluded. A rechallenge can be dangerous and should always be well contemplated or even avoided.

Efficacy, safety and biomarker analysis of durvalumab in patients with mismatch-repair deficient or microsatellite instability-high solid tumours.

BACKGROUND: In this study we aimed to evaluate the efficacy and safety of the PD-L1 inhibitor durvalumab across various mismatch repair deficient (dMMR) or microsatellite instability-high (MSI-H) tumours in the Drug Rediscovery Protocol (DRUP). This is a clinical study in which patients are treated with drugs outside their labeled indication, based on their tumour molecular profile. PATIENTS AND METHODS: Patients with dMMR/MSI-H solid tumours who had exhausted all standard of care options were eligible. Patients were treated with durvalumab. The primary endpoints were clinical benefit ((CB): objective response (OR) or stable disease ≥16 weeks) and safety. Patients were enrolled using a Simon like 2-stage model, with 8 patients in stage 1, up to 24 patients in stage 2 if at least 1/8 patients had CB in stage 1. At baseline, fresh frozen biopsies were obtained for biomarker analyses. RESULTS: Twenty-six patients with 10 different cancer types were included. Two patients (2/26, 8%) were considered as non-evaluable for the primary endpoint. CB was observed in 13 patients (13/26, 50%) with an OR in 7 patients (7/26, 27%). The remaining 11 patients (11/26, 42%) had progressive disease. Median progression-free survival and median overall survival were 5 months (95% CI, 2-not reached) and 14 months (95% CI, 5-not reached), respectively. No unexpected toxicity was observed. We found a significantly higher structural variant (SV) burden in patients without CB. Additionally, we observed a significant enrichment of JAK1 frameshift mutations and a significantly lower IFN-γ expression in patients without CB. CONCLUSION: Durvalumab was generally well-tolerated and provided durable responses in pre-treated patients with dMMR/MSI-H solid tumours. High SV burden, JAK1 frameshift mutations and low IFN-γ expression were associated with a lack of CB; this provides a rationale for larger studies to validate these findings. TRIAL REGISTRATION: Clinical trial registration: NCT02925234. First registration date: 05/10/2016.

WEE1 inhibitor adavosertib in combination with carboplatin in advanced TP53 mutated ovarian cancer: A biomarker-enriched phase II study.

OBJECTIVE: In the first part of this phase II study (NCT01164995), the combination of carboplatin and adavosertib (AZD1775) was shown to be safe and effective in patients with TP53 mutated platinum-resistant ovarian cancer (PROC). Here, we present the results of an additional safety and efficacy cohort and explore predictive biomarkers for resistance and response to this combination treatment. METHODS: This is a phase II, open-label, non-randomized study. Patients with TP53 mutated PROC received carboplatin AUC 5 mg/ ml·min intravenously and adavosertib 225 mg BID orally for 2.5 days in a 21-day cycle. The primary objective is to determine the efficacy and safety of carboplatin and adavosertib. Secondary objectives include progression-free survival (PFS), changes in circulating tumor cells (CTC) and exploration of genomic alterations. RESULTS: Thirty-two patients with a median age of 63 years (39-77 years) were enrolled and received treatment. Twenty-nine patients were evaluable for efficacy. Bone marrow toxicity, nausea and vomiting were the most common adverse events. Twelve patients showed partial response (PR) as best response, resulting in an objective ORR of 41% in the evaluable patients (95% CI: 23%-61%). The median PFS was 5.6 months (95% CI: 3.8-10.3). In patients with tumors harboring CCNE1 amplification, treatment efficacy was slightly but not significantly better. CONCLUSIONS: Adavosertib 225 mg BID for 2.5 days and carboplatin AUC 5 could be safely combined and showed anti-tumor efficacy in patients with PROC. However, bone marrow toxicity remains a point of concern, since this is the most common reason for dose reductions and dose delays.

Mutational profiles associated with resistance in patients with BRAFV600E mutant colorectal cancer treated with cetuximab and encorafenib +/- binimetinib or alpelisib.

BACKGROUND: Treatment strategies inhibiting BRAF in combination with EGFR have been developed in patients with BRAFV600E mutant metastatic colorectal cancer, but intrinsic and secondary resistance remains a challenge. We aimed to investigate which genetic alterations cause intrinsic non-response and/or acquired resistance in these patients receiving therapies consisting of a backbone of BRAF and EGFR inhibition. METHODS: This was a cohort study on genetic alterations in patients with BRAFV600E mutant advanced colorectal cancer treated with inhibitors of the MAPK pathway. We examined tumour tissue for genetic alterations at baseline, during treatment and at progression. RESULTS: In total, 37 patients were included in this cohort. Genetic alterations in EGFR and in PIK3CA are associated with non-response. A greater fraction of non-responders (75%) versus responders (46%) had at least one genetic alteration in other genes than TP53, APC or BRAF. Secondary resistance mutations (n = 16 patients) were observed most frequently in the PI3K pathway (n = 6) and in receptor tyrosine kinases (n = 4), leading to increased upstream signalling. CONCLUSIONS: Genetic alterations in the PI3K and upstream receptor tyrosine kinases were mostly associated with intrinsic and acquired resistance. By understanding these alterations, simultaneous or alternating treatments with targeted inhibitors might improve response duration.

Phase 1 study of the pan-HER inhibitor dacomitinib plus the MEK1/2 inhibitor PD-0325901 in patients with KRAS-mutation-positive colorectal, non-small-cell lung and pancreatic cancer.

BACKGROUND: Mutations in KRAS result in a constitutively activated MAPK pathway. In KRAS-mutant tumours existing treatment options, e.g. MEK inhibition, have limited efficacy due to resistance through feedback activation of epidermal growth factor receptors (HER). METHODS: In this Phase 1 study, the pan-HER inhibitor dacomitinib was combined with the MEK1/2 inhibitor PD-0325901 in patients with KRAS-mutant colorectal, pancreatic and non-small-cell lung cancer (NSCLC). Patients received escalating oral doses of once daily dacomitinib and twice daily PD-0325901 to determine the recommended Phase 2 dose (RP2D). (Clinicaltrials.gov: NCT02039336). RESULTS: Eight out of 41 evaluable patients (27 colorectal cancer, 11 NSCLC and 3 pancreatic cancer) among 8 dose levels experienced dose-limiting toxicities. The RP2D with continuous dacomitinib dosing was 15 mg of dacomitinib plus 6 mg of PD-0325901 (21 days on/7 days off), but major toxicity, including rash (85%), diarrhoea (88%) and nausea (63%), precluded long-term treatment. Therefore, other intermittent schedules were explored, which only slightly improved toxicity. Tumour regression was seen in eight patients with the longest treatment duration (median 102 days) in NSCLC. CONCLUSIONS: Although preliminary signs of antitumour activity in NSCLC were seen, we do not recommend further exploration of this combination in KRAS-mutant patients due to its negative safety profile.

The Use of Microdosing for In vivo Phenotyping of Cytochrome P450 Enzymes: Where Do We Stand? A Narrative Review.

Cytochrome P450 (CYP) enzymes play a central role in the elimination of approximately 80% of all clinically used drugs. Differences in CYP enzyme activity between individuals can contribute to interindividual variability in exposure and, therefore, treatment outcome. In vivo CYP enzyme activity could be determined with phenotyping. Currently, (sub)therapeutic doses are used for in vivo phenotyping, which can lead to side effects. The use of microdoses (100 µg) for in vivo phenotyping for CYP enzymes could overcome the limitations associated with the use of (sub)therapeutic doses of substrates. The aim of this review is to provide a critical overview of the application of microdosing for in vivo phenotyping of CYP enzymes. A literature search was performed to find drug-drug interaction studies of CYP enzyme substrates that used microdoses of the respective substrates. A substrate was deemed sensitive to changes in CYP enzyme activity when the pharmacokinetics of the substrate significantly changed during inhibition and induction of the enzyme. On the basis of the currently available evidence, the use of microdosing for in vivo phenotyping for subtypes CYP1A2, CYP2C9, CYP2D6, and CYP2E1 is not recommended. Microdosing can be used for the in vivo phenotyping of CYP2C19 and CYP3A. The recommended microdose phenotyping test for CYP2C19 is measuring the omeprazole area-under-the-concentration-time curve over 24 h (AUC0-24) after administration of a single 100 µg dose. CYP3A activity could be best determined with a 0.1-75 µg dose of midazolam, and subsequently measuring AUC extrapolated to infinity (AUC∞) or clearance. Moreover, there are two metrics available for midazolam using a limited sampling strategy: AUC over 10 h (AUC0-10) and AUC from 2 to 4 h (AUC2-4).

Is Higher Docetaxel Clearance in Prostate Cancer Patients Explained by Higher CYP3A? An In Vivo Phenotyping Study with Midazolam.

Patients with prostate cancer (PCa) have a lower docetaxel exposure for both intravenous (1.8-fold) and oral administration (2.4-fold) than patients with other solid cancers, which could influence efficacy and toxicity. An altered metabolism by cytochrome P450 3A (CYP3A) due to castration status might explain the observed difference in docetaxel pharmacokinetics. In this in vivo phenotyping, pharmacokinetic study, CYP3A activity defined by midazolam clearance (CL) was compared between patients with PCa and male patients with other solid tumors. All patients with solid tumors who did not use CYP3A-modulating drugs were eligible for participation. Patients received 2 mg midazolam orally and 1 mg midazolam intravenously on 2 consecutive days. Plasma concentrations were measured with a validated liquid chromatography-tandem mass spectrometry method. Genotyping was performed for CYP3A4 and CYP3A5. Nine patients were included in each group. Oral midazolam CL was 1.26-fold higher in patients with PCa compared to patients with other solid tumors (geometric mean [coefficient of variation], 94.1 [33.5%] L/h vs 74.4 [39.1%] L/h, respectively; P = .08). Intravenous midazolam CL did not significantly differ between the 2 groups (P = .93). Moreover, the metabolic ratio of midazolam to 1'-hydroxy midazolam did not differ between the 2 groups for both oral administration (P = .67) and intravenous administration (P = .26). CYP3A4 and CYP3A5 genotypes did not influence midazolam pharmacokinetics. The observed difference in docetaxel pharmacokinetics between both patient groups therefore appears to be explained neither by a difference in midazolam CL nor by a difference in metabolic conversion rate of midazolam.

A proof-of-concept study of sequential treatment with the HDAC inhibitor vorinostat following BRAF and MEK inhibitors in BRAFV600mutated melanoma.

PURPOSE: Development of resistance limits the clinical benefit of BRAF and MEK inhibitors (BRAFi/MEKi) in BRAFV600 mutated melanoma. It has been shown that short-term treatment (14 days) with vorinostat was able to initiate apoptosis of the resistant tumor cells. We aimed to assess the anti-tumor activity of sequential treatment with vorinostat following BRAFi/MEKi in patients with BRAFV600 melanoma who progressed after initial response to BRAFi/MEKi. PATIENTS AND METHODS: Patients with BRAFi/MEKi resistant BRAFV600 melanoma were treated with vorinostat 360 mg QD for 14 days followed by BRAFi/MEKi. The primary endpoint was an objective response rate of progressive lesions of at least 30% according to RECIST 1.1. Secondary endpoints included progression-free survival (PFS), overall survival (OS), safety, pharmacokinetics of vorinostat and translational molecular analyses using ctDNA and tumor biopsies. RESULTS: Twenty-six patients with progressive BRAFi/MEKi resistant BRAFV600 mutated melanoma received treatment with vorinostat. Twenty-two patients were evaluable for response. The ORR was 9% (one complete response for 31.2 months and one partial response for 14.9 months. Median PFS and OS were 1.4 and 5.4 months, respectively. Common adverse events were fatigue (23%) and nausea (19%). ctDNA analysis showed emerging secondary mutations in NRAS and MEK in eight patients at time of BRAFi/MEKi resistance. Elimination of these mutations by vorinostat treatment was observed in three patients. CONCLUSIONS: Intermittent treatment with vorinostat in patients with resistant BRAFV600mutated melanoma is well tolerated. Although the primary endpoint of this study was not met, durable anti-tumor responses were observed in a minority of patients (9%).

Pharmacokinetic boosting of olaparib: A randomised, cross-over study (PROACTIVE-study).

BACKGROUND: Pharmacokinetic (PK) boosting is the intentional use of a drug-drug interaction to enhance systemic drug exposure. PK boosting of olaparib, a CYP3A-substrate, has the potential to reduce PK variability and financial burden. The aim of this study was to investigate equivalence of a boosted, reduced dose of olaparib compared to the non-boosted standard dose. METHODS: This cross-over, multicentre trial compared olaparib 300 mg twice daily (BID) with olaparib 100 mg BID boosted with the strong CYP3A-inhibitor cobicistat 150 mg BID. Patients were randomised to the standard therapy followed by the boosted therapy, or vice versa. After seven days of each therapy, dense PK sampling was performed for noncompartmental PK analysis. Equivalence was defined as a 90% Confidence Interval (CI) of the geometric mean ratio (GMR) of the boosted versus standard therapy area under the plasma concentration-time curve (AUC0-12 h) within no-effect boundaries. These boundaries were set at 0.57-1.25, based on previous pharmacokinetic studies with olaparib capsules and tablets. RESULTS: Of 15 included patients, 12 were eligible for PK analysis. The GMR of the AUC0-12 h was 1.45 (90% CI 1.27-1.65). No grade ≥3 adverse events were reported during the study. CONCLUSIONS: Boosting a 100 mg BID olaparib dose with cobicistat increases olaparib exposure 1.45-fold, compared to the standard dose of 300 mg BID. Equivalence of the boosted olaparib was thus not established. Boosting remains a promising strategy to reduce the olaparib dose as cobicistat increases olaparib exposure Adequate tolerability of the boosted therapy with higher exposure should be established.

First-in-human phase I study of the OX40 agonist GSK3174998 with or without pembrolizumab in patients with selected advanced solid tumors (ENGAGE-1).

BACKGROUND: The phase I first-in-human study ENGAGE-1 evaluated the humanized IgG1 OX40 agonistic monoclonal antibody GSK3174998 alone (Part 1 (P1)) or in combination with pembrolizumab (Part 2 (P2)) in patients with advanced solid tumors. METHODS: GSK3174998 (0.003-10 mg/kg) ± pembrolizumab (200 mg) was administered intravenously every 3 weeks using a continuous reassessment method for dose escalation. Primary objectives were safety and tolerability; secondary objectives included pharmacokinetics, immunogenicity, pharmacodynamics, and clinical activity. RESULTS: 138 patients were enrolled (45 (P1) and 96 (P2, including 3 crossovers)). Treatment-related adverse events occurred in 51% (P1) and 64% (P2) of patients, fatigue being the most common (11% and 24%, respectively). No dose-toxicity relationship was observed, and maximum-tolerated dose was not reached. Dose-limiting toxicities (P2) included Grade 3 (G3) pleural effusion and G1 myocarditis with G3 increased troponin. GSK3174998 ≥0.3 mg/kg demonstrated pharmacokinetic linearity and >80% receptor occupancy on circulating T cells; 0.3 mg/kg was selected for further evaluation. Limited clinical activity was observed for GSK3174998 (P1: disease control rate (DCR) ≥24 weeks 9%) and was not greater than that expected for pembrolizumab alone (P2: overall response rate 8%, DCR ≥24 weeks 28%). Multiplexed immunofluorescence data from paired biopsies suggested that increased infiltration of natural killer (NK)/natural killer T (NKT) cells and decreased regulatory T cells (Tregs) in the tumor microenvironment may contribute to clinical responses: CD16+CD56-CD134+ NK /NKT cells and CD3+CD4+FOXP3+CD134+ Tregs exhibited the largest magnitude of change on treatment, whereas CD3+CD8+granzyme B+PD-1+CD134+ cytotoxic T cells were the least variable. Tumor gene expression profiling revealed an upregulation of inflammatory responses, T-cell proliferation, and NK cell function on treatment with some inflammatory cytokines upregulated in peripheral blood. However, target engagement, evidenced by pharmacologic activity in peripheral blood and tumor tissue, did not correlate with clinical efficacy. The low number of responses precluded identifying a robust biomarker signature predictive of response. CONCLUSIONS: GSK3174998±pembrolizumab was well tolerated over the dose range tested and demonstrated target engagement. Limited clinical activity does not support further development of GSK3174998±pembrolizumab in advanced cancers. TRIAL REGISTRATION NUMBER: NCT02528357.

Lapatinib for advanced or metastatic breast cancer.

Lapatinib is a potent reversible and selective inhibitor of the tyrosine kinase domains of epidermal growth factor receptor and human epidermal growth factor receptor (HER)-2 that exerts its action by competitive binding to the intracellular ATP-binding site of the receptor. It is registered for the treatment of advanced or metastatic HER-2+ breast cancer in combination with capecitabine and for hormone receptor-positive breast cancer in combination with an aromatase inhibitor. Lapatinib administered orally once daily is moderately to well tolerated, with rash and gastrointestinal adverse events as the main toxicities. In studies on the efficacy of lapatinib, direct comparisons between lapatinib and trastuzumab are lacking. Results of ongoing randomized phase III studies with lapatinib or trastuzumab in combination with taxanes as first-line agents for metastatic breast cancer as well as in the neoadjuvant and adjuvant settings are awaited.

Phase I study of lapatinib plus trametinib in patients with KRAS-mutant colorectal, non-small cell lung, and pancreatic cancer.

PURPOSE: KRAS oncogene mutations cause sustained signaling through the MAPK pathway. Concurrent inhibition of MEK, EGFR, and HER2 resulted in complete inhibition of tumor growth in KRAS-mutant (KRASm) and PIK3CA wild-type tumors, in vitro and in vivo. In this phase I study, patients with advanced KRASm and PIK3CA wild-type colorectal cancer (CRC), non-small cell lung cancer (NSCLC), and pancreatic cancer, were treated with combined lapatinib and trametinib to assess the recommended phase 2 regimen (RP2R). METHODS: Patients received escalating doses of continuous or intermittent once daily (QD) orally administered lapatinib and trametinib, starting at 750 mg and 1 mg continuously, respectively. RESULTS: Thirty-four patients (16 CRC, 15 NSCLC, three pancreatic cancers) were enrolled across six dose levels and eight patients experienced dose-limiting toxicities, including grade 3 diarrhea (n = 2), rash (n = 2), nausea (n = 1), multiple grade 2 toxicities (n = 1), and aspartate aminotransferase elevation (n = 1), resulting in the inability to receive 75% of planned doses (n = 2) or treatment delay (n = 2). The RP2R with continuous dosing was 750 mg lapatinib QD plus 1 mg trametinib QD and with intermittent dosing 750 mg lapatinib QD and trametinib 1.5 mg QD 5 days on/2 days off. Regression of target lesions was seen in 6 of the 24 patients evaluable for response, with one confirmed partial response in NSCLC. Pharmacokinetic results were as expected. CONCLUSION: Lapatinib and trametinib could be combined in an intermittent dosing schedule in patients with manageable toxicity. Preliminary signs of anti-tumor activity in NSCLC have been observed and pharmacodynamic target engagement was demonstrated.

TAS-102 for Treatment of Advanced Colorectal Cancers That Are No Longer Responding to Other Therapies.

TAS-102 is a novel oral formulation of trifluridine (TFT) and tipiracil hydrochloride (TPI), a thymidine phosphorylase inhibitor. TFT was originally synthesized in the 1960s and is a nucleoside analogue that impedes DNA synthesis by inhibition of thymidylate synthase. TFT's main mechanism of action, however, seems to be its incorporation into DNA, which distinguishes TFT from current well-known antimetabolites like 5-fluorouracil (5-FU). The rapid degradation of TFT brought initial clinical development to a halt, but TFT reentered clinical trials when addition of a TPI was found to improve the bioavailability of TFT. The combined TFT-TPI formulation was tested in patients with treatment-refractory metastatic colorectal cancer in the randomized phase III RECOURSE study. Compared with placebo, TAS-102 was associated with an overall survival (OS) and progression-free survival (PFS) benefit and a 32% reduction in risk of death [median OS, 7.1 (95% CI, 6.5-7.8) vs. 5.3 months (95% CI, 4.6-6.0); median PFS, 2.0 (95% CI, 1.9-2.1) vs. 1.7 months (95% CI, 1.7-1.8); HR for death, 0.68 (95% CI, 0.58-0.81, P < 0.001)]. Based on the results of this pivotal trial and supported by results from an earlier phase II study, TAS-102 recently gained FDA approval. This article reviews the development of TAS-102 and its therapeutic value for the proposed indication. Clin Cancer Res; 22(12); 2835-9. ©2016 AACR.

[Recurrent upper respiratory tract infections during and after rituximab therapy]. / Recidiverende luchtweginfecties tijdens en na rituximab.

Rituximab maintenance therapy is indicated for the treatment of patients with non-Hodgkin's lymphoma (NHL) who responded to induction therapy. More than 10% of patients will develop rituximab-induced upper respiratory tract infections (URTIs). These infections are usually mild in patients receiving first-line or second-line treatment. Heavily pretreated patients sometimes undergo additional rituximab maintenance therapy. We describe three female patients aged 53, 43 and 42 years who were successfully treated with rituximab maintenance therapy after chemotherapy for three or more recurrences of NHL. These patients developed more serious recurrent URTIs due to rituximab-induced long-term hypogammaglobulinaemia. In one patient, serum IgG levels continued to decline for four years after rituximab therapy. Long-term immunoglobulin substitution was needed to treat these patients. Physicians should be aware that URTIs may develop in heavily pretreated patients even years after rituximab maintenance therapy and substitution with immunoglobulin may be warranted.

[Hyperglycaemia during treatment with everolimus]. / Hyperglykemie bij gebruik van everolimus.

BACKGROUND: Everolimus is an orally administered anti-cancer drug that inhibits the mammalian target of rapamycin (mTOR) signal transduction route. Use of everolimus may be associated with insulin resistance, manifesting in impaired glucose tolerance or hyperglycaemia. CASE DESCRIPTION: A 74-year-old female patient with a locally recurrent breast cancer developed hyperglycaemia, which started 2 weeks after the initiation of treatment with everolimus 10 mg once daily. Metformin and insulin were administered to restore normoglycaemia. CONCLUSION: At the initiation of treatment with an mTOR inhibitor such as everolimus the treating physician should be aware of the occurrence of hyperglycaemia. Metformin is then the medicine of first choice.

Breath tests to phenotype drug disposition in oncology.

Breath tests (BTs) have been investigated as diagnostic tools to phenotype drug disposition in cancer patients in the pursuit to individualize drug treatment. The choice of the right phenotype probe is crucial and depends on the metabolic pathway of the anticancer agent of interest. BTs using orally or intravenously administered selective non-radioactive (13)C-labeled probes to non-invasively evaluate dihydropyrimidine dehydrogenase, cytochrome P450 (CYP) 3A4, and CYP2D6 enzyme activity have been published. Clinically, a (13)C-dextromethorphan BT to predict endoxifen levels in breast cancer patients and a (13)C-uracil BT to predict fluoropyrimidine toxicity in colorectal cancer patients are most promising. However, the clinical benefit and cost effectiveness of these phenotype BTs need to be determined in order to make the transition from an experimental setting to clinical practice as companion diagnostic tests.

Phenotyping drug disposition in oncology.

Efficacy and toxicity of anticancer agents are highly variable between patients and variation in drug disposition is thought to be an important determinant. Genetics, physiology, and environment all are underlying factors contributing to this variation. Phenotyping drug metabolizing enzymes and drug transporters by using in vivo probes is a method that can be used to individualize drug therapy. This review discusses drug disposition of anticancer agents and the potential of phenotyping probes for phase I, II metabolic enzymes, and drug transporters in oncology.