Utility of the 70-Gene MammaPrint Assay for Prediction of Benefit From Extended Letrozole Therapy in the NRG Oncology/NSABP B-42 Trial.

PURPOSE: MammaPrint (MP) determines distant metastatic risk and may improve patient selection for extended endocrine therapy (EET). This study examined MP in predicting extended letrozole therapy (ELT) benefit in patients with early-stage breast cancer (BC) from the NSABP B-42 trial. PATIENTS AND METHODS: MP was tested in 1,866 patients randomly assigned to receive ELT or placebo. The primary end point was distant recurrence (DR). Secondary end points were disease-free survival (DFS) and BC-free interval (BCFI). Tumors were classified as MP high risk (MP-HR) or low risk (MP-LR). MP-LR tumors were further classified as ultralow risk (MP-UL) or low non-ultralow risk (MP-LNUL). RESULTS: There was no statistically significant difference in ELT benefit on DR between MP-HR and MP-LR (interaction P = .38). MP-LR tumors (n = 1,160) exhibited a statistically significant 10-year benefit of 3.7% for DR (hazard ratio [HR], 0.43 [95% CI, 0.25 to 0.74]; P = .002), whereas MP-HR tumors (n = 706) exhibited a nonsignificant 2.4% benefit (HR, 0.65 [95% CI, 0.34 to 1.24]; P = .19). The 10-year ELT benefit was significant for DFS (7.8%) and BCFI (7.0%) for MP-LR tumors, whereas MP-HR tumors did not significantly benefit (interaction DFS: P = .015, BCFI: P = .006). In exploratory analysis, the 10-year ELT benefit was significant and more pronounced in MP-LNUL (n = 908) tumors: 4.0% for DR, 9.5% for DFS, and 7.9% for BCFI; the benefit in MP-UL (n = 252) tumors was not significant: 3% for DR, 1.8% for DFS, and 4.1% for BCFI. CONCLUSION: The primary hypothesis of predictive ability of MP on DR was not confirmed. However, the secondary outcomes demonstrated MP was predictive of ELT response and identified a subset of patients with early-stage hormone receptor-positive BC (MP-LR) with improved outcomes from ELT. These data could have important clinical implications in patient selection beyond clinical risk assessment for EET.

Optimizing Postneoadjuvant Treatment in Patients With Early Breast Cancer Achieving Pathologic Complete Response.

pCR should be integrated with other prognostic factors to optimize postneoadjuvant treatments in BC.

Sequencing of Endocrine and Targeted Therapies in Hormone-Sensitive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer.

The Oncology Grand Rounds series is designed to place original reports published in the Journal into clinical context. A case presentation is followed by a description of diagnostic and management challenges, a review of the relevant literature, and a summary of the authors' suggested management approaches. The goal of this series is to help readers better understand how to apply the results of key studies, including those published in Journal of Clinical Oncology, to patients seen in their own clinical practice.Optimizing the selection and sequencing of endocrine and targeted therapies for hormone-sensitive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer is a rapidly evolving field owing in large part to an increasing pace of drug development coupled with a greater understanding of the genomic drivers of breast cancer. The recently published results from the MAINTAIN clinical trial begin to answer an important question in this patient population-can the well-established benefit with first-line cyclin-dependent kinase 4/6 (CDK 4/6) inhibitors be stretched further by continuing this drug class beyond progression and selecting an alternate endocrine therapy partner? We present a case of a patient with hormone-sensitive HER2 low metastatic breast cancer who underwent circulating tumor DNA next-generation sequencing to better inform her treatment options after progression on first-line therapy with a CDK 4/6 inhibitor and aromatase inhibitor. Our clinical approach in this patient population prioritizes the identification of actionable mutations with high-quality evidence for efficacy on the basis of clinical trials post-CDK 4/6 inhibitors, while balancing comorbidities and patient priorities for care. Several recent clinical trials discussed herein present clinically meaningful results linking emerging targeted therapies to actionable alterations in PIK3CA, ESR1, AKT1, and PTEN. Continued drug development in this space delays time to treatment with chemotherapy, and hopefully contributes to maintaining a high quality of life for these patients on primarily oral-based therapy.

Overall survival with neratinib after trastuzumab-based adjuvant therapy in HER2-positive breast cancer (ExteNET): A randomised, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: ExteNET showed that neratinib, an irreversible pan-HER tyrosine kinase inhibitor, given for 1 year after trastuzumab-based therapy significantly improved invasive disease-free survival in women with early-stage HER2-positive breast cancer. We report the final analysis of overall survival in ExteNET. METHODS: In this international, randomised, double-blind, placebo-controlled, phase 3 trial, women aged 18 years or older with stage 1-3c (amended to stage 2-3c) HER2-positive breast cancer who had completed neoadjuvant and adjuvant chemotherapy plus trastuzumab were eligible. Patients were randomly assigned to oral neratinib 240 mg/day or placebo for 1 year. Randomisation was stratified according to hormone receptor (HR) status (HR-positive vs. HR-negative), nodal status (0, 1-3 or 4+), and trastuzumab regimen (sequentially vs. concurrently with chemotherapy). Overall survival was analysed by intention to treat. ExteNET is registered (Clinicaltrials.gov: NCT00878709) and is complete. RESULTS: Between July 9, 2009, and October 24, 2011, 2840 women received neratinib (n = 1420) or placebo (n = 1420). After a median follow-up of 8.1 (IQR, 7.0-8.8) years, 127 patients (8.9%) in the neratinib group and 137 patients (9.6%) in the placebo group in the intention-to-treat population had died. Eight-year overall survival rates were 90.1% (95% CI 88.3-91.6) with neratinib and 90.2% (95% CI 88.4-91.7) with placebo (stratified hazard ratio 0.95; 95% CI 0.75-1.21; p = 0.6914). CONCLUSIONS: Overall survival in the extended adjuvant setting was comparable for neratinib and placebo after a median follow-up of 8.1 years in women with early-stage HER2-positive breast cancer.

Proteomic analysis of archival breast cancer clinical specimens identifies biological subtypes with distinct survival outcomes.

Despite advances in genomic classification of breast cancer, current clinical tests and treatment decisions are commonly based on protein level information. Formalin-fixed paraffin-embedded (FFPE) tissue specimens with extended clinical outcomes are widely available. Here, we perform comprehensive proteomic profiling of 300 FFPE breast cancer surgical specimens, 75 of each PAM50 subtype, from patients diagnosed in 2008-2013 (n = 178) and 1986-1992 (n = 122) with linked clinical outcomes. These two cohorts are analyzed separately, and we quantify 4214 proteins across all 300 samples. Within the aggressive PAM50-classified basal-like cases, proteomic profiling reveals two groups with one having characteristic immune hot expression features and highly favorable survival. Her2-Enriched cases separate into heterogeneous groups differing by extracellular matrix, lipid metabolism, and immune-response features. Within 88 triple-negative breast cancers, four proteomic clusters display features of basal-immune hot, basal-immune cold, mesenchymal, and luminal with disparate survival outcomes. Our proteomic analysis characterizes the heterogeneity of breast cancer in a clinically-applicable manner, identifies potential biomarkers and therapeutic targets, and provides a resource for clinical breast cancer classification.

21-Gene Assay to Inform Chemotherapy Benefit in Node-Positive Breast Cancer.

BACKGROUND: The recurrence score based on the 21-gene breast-cancer assay has been clinically useful in predicting a chemotherapy benefit in hormone-receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative, axillary lymph-node-negative breast cancer. In women with positive lymph-node disease, the role of the recurrence score with respect to predicting a benefit of adjuvant chemotherapy is unclear. METHODS: In a prospective trial, we randomly assigned women with hormone-receptor-positive, HER2-negative breast cancer, one to three positive axillary lymph nodes, and a recurrence score of 25 or lower (scores range from 0 to 100, with higher scores indicating a worse prognosis) to endocrine therapy only or to chemotherapy plus endocrine (chemoendocrine) therapy. The primary objective was to determine the effect of chemotherapy on invasive disease-free survival and whether the effect was influenced by the recurrence score. Secondary end points included distant relapse-free survival. RESULTS: A total of 5083 women (33.2% premenopausal and 66.8% postmenopausal) underwent randomization, and 5018 participated in the trial. At the prespecified third interim analysis, the chemotherapy benefit with respect to increasing invasive disease-free survival differed according to menopausal status (P = 0.008 for the comparison of chemotherapy benefit in premenopausal and postmenopausal participants), and separate prespecified analyses were conducted. Among postmenopausal women, invasive disease-free survival at 5 years was 91.9% in the endocrine-only group and 91.3% in the chemoendocrine group, with no chemotherapy benefit (hazard ratio for invasive disease recurrence, new primary cancer [breast cancer or another type], or death, 1.02; 95% confidence interval [CI], 0.82 to 1.26; P = 0.89). Among premenopausal women, invasive disease-free survival at 5 years was 89.0% with endocrine-only therapy and 93.9% with chemoendocrine therapy (hazard ratio, 0.60; 95% CI, 0.43 to 0.83; P = 0.002), with a similar increase in distant relapse-free survival (hazard ratio, 0.58; 95% CI, 0.39 to 0.87; P = 0.009). The relative chemotherapy benefit did not increase as the recurrence score increased. CONCLUSIONS: Among premenopausal women with one to three positive lymph nodes and a recurrence score of 25 or lower, those who received chemoendocrine therapy had longer invasive disease-free survival and distant relapse-free survival than those who received endocrine-only therapy, whereas postmenopausal women with similar characteristics did not benefit from adjuvant chemotherapy. (Funded by the National Cancer Institute and others; RxPONDER ClinicalTrials.gov number, NCT01272037.).

PIK3CA alterations and benefit with neratinib: analysis from the randomized, double-blind, placebo-controlled, phase III ExteNET trial.

BACKGROUND: Neratinib is an irreversible pan-HER tyrosine kinase inhibitor that inhibits PI3K/Akt and MAPK signaling pathways after HER2 receptor activation. The ExteNET study showed that neratinib significantly improved 5-year invasive disease-free survival (iDFS) in women who completed trastuzumab-based adjuvant therapy for early breast cancer (EBC). We assessed the prognostic and predictive significance of PIK3CA alterations in patients in ExteNET. METHODS: Participants were women aged ≥ 18 years (≥ 20 years in Japan) with stage 1-3c (modified to stage 2-3c in February 2010) operable breast cancer, who had completed (neo)adjuvant chemotherapy plus trastuzumab ≤ 2 years before randomization, with no evidence of disease recurrence or metastatic disease at study entry. Patients were randomized to oral neratinib 240 mg/day or placebo for 1 year. Formalin-fixed, paraffin-embedded primary tumor specimens underwent polymerase chain reaction (PCR) PIK3CA testing for two hotspot mutations in exon 9, one hot-spot mutation in exon 20, and fluorescence in situ hybridization (FISH) analysis for PIK3CA amplification. The primary endpoint (iDFS) was tested with log-rank test and hazard ratios (HRs) estimated using Cox proportional-hazards models. RESULTS: Among the intent-to-treat population (n = 2840), tumor specimens were available for PCR testing (991 patients) and PIK3CA FISH (702 patients). Overall, 262 samples were PIK3CA altered: 201 were mutated (77%), 52 (20%) were amplified, and 9 (3%) were mutated and amplified. iDFS was non-significantly worse in placebo-treated patients with altered vs wild-type PIK3CA (HR 1.34; 95% CI 0.72-2.50; P = 0.357). Neratinib's effect over placebo was significant in patients with PIK3CA-altered tumors (HR 0.41; 95% CI 0.17-0.90, P = 0.028) but not PIK3CA wild-type tumors (HR 0.72; 95% CI 0.36-1.41; P = 0.34). The interaction test was non-significant (P = 0.309). CONCLUSIONS: Although there was a greater absolute risk reduction associated with neratinib treatment of patients with PIK3CA-altered tumors in ExteNET, current data do not support PIK3CA alteration as a predictive biomarker of response to neratinib in HER2-positive EBC. TRIAL REGISTRATION: ClinicalTrials.gov , NCT00878709 . Trial registered April 9, 2009.

Neratinib after trastuzumab-based adjuvant therapy in HER2-positive breast cancer (ExteNET): 5-year analysis of a randomised, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: ExteNET showed that 1 year of neratinib, an irreversible pan-HER tyrosine kinase inhibitor, significantly improves 2-year invasive disease-free survival after trastuzumab-based adjuvant therapy in women with HER2-positive breast cancer. We report updated efficacy outcomes from a protocol-defined 5-year follow-up sensitivity analysis and long-term toxicity findings. METHODS: In this ongoing randomised, double-blind, placebo-controlled, phase 3 trial, eligible women aged 18 years or older (≥20 years in Japan) with stage 1-3c (modified to stage 2-3c in February, 2010) operable breast cancer, who had completed neoadjuvant and adjuvant chemotherapy plus trastuzumab with no evidence of disease recurrence or metastatic disease at study entry. Patients who were eligible patients were randomly assigned (1:1) via permuted blocks stratified according to hormone receptor status (hormone receptor-positive vs hormone receptor-negative), nodal status (0 vs 1-3 vs or ≥4 positive nodes), and trastuzumab adjuvant regimen (given sequentially vs concurrently with chemotherapy), then implemented centrally via an interactive voice and web-response system, to receive 1 year of oral neratinib 240 mg/day or matching placebo. Treatment was given continuously for 1 year, unless disease recurrence or new breast cancer, intolerable adverse events, or consent withdrawal occurred. Patients, investigators, and trial funder were masked to treatment allocation. The predefined endpoint of the 5-year analysis was invasive disease-free survival, analysed by intention to treat. ExteNET is registered with ClinicalTrials.gov, number NCT00878709, and is closed to new participants. FINDINGS: Between July 9, 2009, and Oct 24, 2011, 2840 eligible women with early HER2-positive breast cancer were recruited from community-based and academic institutions in 40 countries and randomly assigned to receive neratinib (n=1420) or placebo (n=1420). After a median follow-up of 5·2 years (IQR 2·1-5·3), patients in the neratinib group had significantly fewer invasive disease-free survival events than those in the placebo group (116 vs 163 events; stratified hazard ratio 0·73, 95% CI 0·57-0·92, p=0·0083). The 5-year invasive disease-free survival was 90·2% (95% CI 88·3-91·8) in the neratinib group and 87·7% (85·7-89·4) in the placebo group. Without diarrhoea prophylaxis, the most common grade 3-4 adverse events in the neratinib group, compared with the placebo group, were diarrhoea (561 [40%] grade 3 and one [<1%] grade 4 with neratinib vs 23 [2%] grade 3 with placebo), vomiting (grade 3: 47 [3%] vs five [<1%]), and nausea (grade 3: 26 [2%] vs two [<1%]). Treatment-emergent serious adverse events occurred in 103 (7%) women in the neratinib group and 85 (6%) women in the placebo group. No evidence of increased risk of long-term toxicity or long-term adverse consequences of neratinib-associated diarrhoea were identified with neratinib compared with placebo. INTERPRETATION: At the 5-year follow-up, 1 year of extended adjuvant therapy with neratinib, administered after chemotherapy and trastuzumab, significantly reduced the proportion of clinically relevant breast cancer relapses-ie, those that might lead to death, such as distant and locoregional relapses outside the preserved breast-without increasing the risk of long-term toxicity. An analysis of overall survival is planned after 248 events. FUNDING: Wyeth, Pfizer, and Puma Biotechnology.

Basal biomarkers nestin and INPP4b identify intrinsic subtypes accurately in breast cancers that are weakly positive for oestrogen receptor.

AIMS: Recent evidence indicates that weakly positive immunohistochemical staining of oestrogen receptor (ER) is not associated reliably with a luminal subtype, with the majority reclassified as basal-like by gene expression profile. In this study we assessed the capacity of recently identified immunohistochemical markers of basal-like subtype not dependent upon ER status - positive expression of nestin or loss of inositol polyphosphate-4-phosphatase (INPP4b) - to discriminate intrinsic subtypes, focusing on clinically problematic cases with weak ER positivity. METHODS AND RESULTS: Formalin-fixed paraffin-embedded blocks, enriched for large proportions of ER-negative and ER weakly positive breast cancers, were selected from two previous studies conducted in the period 2008-13 and used for (i) RNA extraction for 50-gene subtype predictor (PAM50) intrinsic subtyping and (ii) tissue microarray construction for immunohistochemical assessment of nestin and INPP4b. Fifty-eight cases were weakly positive for ER (Allred 3-5), among which 28 (48%) were assigned as basal-like by PAM50 gene expression. In these 58 cases, the nestin/INPP4b panel identified 23 basal-like cases with a positive predictive value of 87% [95% confidence interval (CI) 78-95%] and excluded luminal subtype with a negative predictive value of 95% (95% CI 88-100%). Weakly positive ER patients assigned as basal-like by nestin/INPP4b definition demonstrated a median survival time of 45.8 months, significantly lower than 65 months among other ER weakly positive cases (P = 0.012). CONCLUSIONS: Immunohistochemical assessment of nestin and INPP4b provides an accurate, accessible and inexpensive tool to identify basal-like breast cancer subtype in the clinically problematic setting of weak ER positivity. This panel identifies poor prognosis patients who might need strong considerations for non-endocrine-based therapies.

Neratinib after trastuzumab-based adjuvant therapy in patients with HER2-positive breast cancer (ExteNET): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: Neratinib, an irreversible tyrosine-kinase inhibitor of HER1, HER2, and HER4, has clinical activity in patients with HER2-positive metastatic breast cancer. We aimed to investigate the efficacy and safety of 12 months of neratinib after trastuzumab-based adjuvant therapy in patients with early-stage HER2-positive breast cancer. METHODS: We did this multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 495 centres in Europe, Asia, Australia, New Zealand, and North and South America. Eligible women (aged ≥18 years, or ≥20 years in Japan) had stage 1-3 HER2-positive breast cancer and had completed neoadjuvant and adjuvant trastuzumab therapy up to 2 years before randomisation. Inclusion criteria were amended on Feb 25, 2010, to include patients with stage 2-3 HER2-positive breast cancer who had completed trastuzumab therapy up to 1 year previously. Patients were randomly assigned (1:1) to receive oral neratinib 240 mg per day or matching placebo. The randomisation sequence was generated with permuted blocks stratified by hormone receptor status (hormone receptor-positive [oestrogen or progesterone receptor-positive or both] vs hormone receptor-negative [oestrogen and progesterone receptor-negative]), nodal status (0, 1-3, or ≥4), and trastuzumab adjuvant regimen (sequentially vs concurrently with chemotherapy), then implemented centrally via an interactive voice and web-response system. Patients, investigators, and trial sponsors were masked to treatment allocation. The primary outcome was invasive disease-free survival, as defined in the original protocol, at 2 years after randomisation. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00878709. FINDINGS: Between July 9, 2009, and Oct 24, 2011, we randomly assigned 2840 women to receive neratinib (n=1420) or placebo (n=1420). Median follow-up time was 24 months (IQR 20-25) in the neratinib group and 24 months (22-25) in the placebo group. At 2 year follow-up, 70 invasive disease-free survival events had occurred in patients in the neratinib group versus 109 events in those in the placebo group (stratified hazard ratio 0·67, 95% CI 0·50-0·91; p=0·0091). The 2-year invasive disease-free survival rate was 93·9% (95% CI 92·4-95·2) in the neratinib group and 91·6% (90·0-93·0) in the placebo group. The most common grade 3-4 adverse events in patients in the neratinib group were diarrhoea (grade 3, n=561 [40%] and grade 4, n=1 [<1%] vs grade 3, n=23 [2%] in the placebo group), vomiting (grade 3, n=47 [3%] vs n=5 [<1%]), and nausea (grade 3, n=26 [2%] vs n=2 [<1%]). QT prolongation occurred in 49 (3%) patients given neratinib and 93 (7%) patients given placebo, and decreases in left ventricular ejection fraction (≥grade 2) in 19 (1%) and 15 (1%) patients, respectively. We recorded serious adverse events in 103 (7%) patients in the neratinib group and 85 (6%) patients in the placebo group. Seven (<1%) deaths (four patients in the neratinib group and three patients in the placebo group) unrelated to disease progression occurred after study drug discontinuation. The causes of death in the neratinib group were unknown (n=2), a second primary brain tumour (n=1), and acute myeloid leukaemia (n=1), and in the placebo group were a brain haemorrhage (n=1), myocardial infarction (n=1), and gastric cancer (n=1). None of the deaths were attributed to study treatment in either group. INTERPRETATION: Neratinib for 12 months significantly improved 2-year invasive disease-free survival when given after chemotherapy and trastuzumab-based adjuvant therapy to women with HER2-positive breast cancer. Longer follow-up is needed to ensure that the improvement in breast cancer outcome is maintained. FUNDING: Wyeth, Pfizer, Puma Biotechnology.

Molecular subtype profiling of invasive breast cancers weakly positive for estrogen receptor.

The estrogen receptor (ER) is a key predictive biomarker in the treatment of breast cancer. There is uncertainty regarding the use of hormonal therapy in the setting of weakly positive ER by immunohistochemistry (IHC). We report intrinsic subtype classification on a cohort of ER weakly positive early-stage breast cancers. Consecutive cases of breast cancer treated by primary surgical resection were retrospectively identified from 4 centers that engage in routine external proficiency testing for breast biomarkers. ER-negative (Allred 0 and 2) and ER weakly positive (Allred 3-5) cases were included. Gene expression profiling was performed using qRT-PCR. Intrinsic subtype prediction was made based upon the PAM50 gene expression signature. 148 cases were included in the series: 60 cases originally diagnosed as ER weakly positive and 88 ER negative. Of the cases originally assessed as ER weakly positive, only 6 (10 %) were confirmed to be of luminal subtype by gene expression profiling; the remaining 90 % of cases were classified as basal-like or HER2-enriched subtypes. This was not significantly different than the fraction of luminal cases identified in the IHC ER-negative cohort (5 (5 %) luminal, 83(95 %) non-luminal). Recurrence-free, and overall, survival rates were similar in both groups (p = 0.4 and 0.5, respectively) despite adjuvant hormonal therapy prescribed in the majority (59 %) of weakly positive ER cases. Weak ER expression by IHC is a poor correlate of luminal subtype in invasive breast cancer. In the setting of highly sensitive and robust IHC methodology, cutoffs for ER status determination and subsequent systemic therapy should be revisited.

Randomised, phase II, placebo-controlled, trial of fulvestrant plus vandetanib in postmenopausal women with bone only or bone predominant, hormone-receptor-positive metastatic breast cancer (MBC): the OCOG ZAMBONEY study.

Biomarkers of bone turnover, including urine N-telopeptide (uNTx), have been used as surrogate measures of response to bone-targeted therapies. Vascular endothelial growth factor (VEGF) levels correlate with extent of bone metastases. We assessed whether vandetanib, an inhibitor of VEGF, epidermal growth factor receptor and RET signalling, improved uNTx response when added to fulvestrant (F) in breast cancer patients with bone metastases. Postmenopausal patients with bone predominant, hormone-receptor-positive metastatic breast cancer were randomised to F (500 mg IM days 1, 15, 29, then monthly) with either vandetanib (100 mg PO OD) (FV) or placebo (FP). The primary objective was uNTx response. Secondary objectives included PFS, OS, RECIST response, pain scores and toxicity. Sixty-one patients were allocated to FV and 68 to FP. Out of 127 analyzable patients, an uNTx response occurred in 66 % for FV and 54 % for FP (p = 0.21). No difference was detected between groups for PFS; HR = 0.95 (95 % CI 0.65-1.38) or OS HR = 0.69 (95 % CI 0.37-1.31). For the 62 patients with measurable disease, clinical benefit rates were 41 and 43 %, respectively (p = 0.47). Serious adverse events were similar, 3.3 % for FV versus 5.9 % for FP. Elevated baseline uNTx (>65 nM BCE/mmol Cr) was prognostic for PFS, HR = 1.55 (95 % CI 1.04-2.30) and for OS, HR = 2.32 (95 % CI 1.25-4.33). The addition of vandetanib to fulvestrant did not improve biomarker response, PFS or OS in patients with bone metastases. Baseline bone turnover was prognostic for PFS and OS.

Safety, pharmacokinetics, and efficacy of CPX-1 liposome injection in patients with advanced solid tumors.

PURPOSE: CPX-1 is a novel, liposome-encapsulated formulation of irinotecan and floxuridine designed to prolong in vitro optimized synergistic molar ratios of both drugs postinfusion. This open-label, single-arm, dose-escalating phase I study was designed to determine the maximum tolerated dose and pharmacokinetics of CPX-1 in patients with advanced solid tumors. EXPERIMENTAL DESIGN: Patients received CPX-1 at 30, 60, 100, 150, 210, or 270 units/m(2) (1 unit = 1 mg irinotecan + 0.36 mg floxuridine) infused over 90 minutes every 14 days in 28-day cycles. Pharmacokinetic samples were collected on days 1 and 15 of cycle 1. RESULTS: Thirty-three patients were enrolled, treated, and evaluated for safety; 30 patients were evaluated for response. A 1:1 plasma irinotecan to floxuridine molar ratio was maintained for 8 to 12 hours. Grade 3/4 toxicities included diarrhea (24.2%), neutropenia (12.1%), and hypokalemia (12.1%); 1 patient (270 units/m(2)) died of persistent diarrhea, which led to dehydration and renal failure (grade 5). Partial response occurred in 3 (12%) of the 25 subjects evaluated through Response Evaluation Criteria in Solid Tumors. Progression-free survival lasting >6 months occurred in 9 patients, 6 with colorectal cancer. Among 15 colorectal cancer patients (10 with prior irinotecan), the calculated median progression-free survival was 5.4 months; 11 patients (72.7%) achieved disease control and 2 patients (13%) had partial response. CONCLUSIONS: Outpatient CPX-1 was well tolerated and antitumor activity was shown in patients with advanced solid tumors. The recommended dose for future studies is 210 units/m(2). This is the first clinical evaluation of fixed drug ratio dosing designed to maintain synergistic molar ratios for enhanced therapeutic benefit.