Development and validation of circulating tumour cell enumeration (Epic Sciences) as a prognostic biomarker in men with metastatic castration-resistant prostate cancer

PURPOSE

To evaluate the prognostic significance of circulating tumour cell (CTC) number determined on the Epic Sciences platform in men with metastatic castration-resistant prostate cancer (mCRPC) treated with an androgen receptor signalling inhibitor (ARSI).

PATIENTS AND METHODS

A pre-treatment blood sample was collected from men with progressing mCRPC starting either abiraterone or enzalutamide as a first-, second- or third-line systemic therapy at Memorial Sloan Kettering Cancer Center (Discovery cohort, N = 171) or as a first- or second-line therapy as part of the multicenter PROPHECY trial (NCT02269982) (Validation cohort, N = 107). The measured CTC number was then associated with overall survival (OS) in the Discovery cohort, and progression-free survival (PFS) and OS in the Validation cohort. CTC enumeration was also performed on a concurrently obtained blood sample using the CellSearch® Circulating Tumor Cell Kit.

RESULTS

In the MSKCC Discovery cohort, CTC count was a statistically significant prognostic factor of OS as a dichotomous (<3 CTCs/mL versus ≥ 3 CTCs/mL; hazard ratio [HR] = 1.8 [95% confidence interval {CI} 1.3-3.0]) and a continuous variable when adjusting for line of therapy, presence of visceral metastases, prostate-specific antigen, lactate dehydrogenase and alkaline phosphatase. The findings were validated in an independent datas et from PROPHECY (HR [95% CI] = 1.8 [1.1-3.0] for OS and 1.7 [1.1-2.9] for PFS). A strong correlation was also observed between CTC counts determined in matched samples on the CellSearch® and Epic platforms (r = 0.84).

CONCLUSION

The findings validate the prognostic significance of pretreatment CTC number determined on the Epic Sciences platform for predicting OS in men with progressing mCRPC starting an ARSI.

Circulating tumour cell increase as a biomarker of disease progression in metastatic castration-resistant prostate cancer patients with low baseline CTC counts

Background

The development of treatment response and surrogate biomarkers for advanced prostate cancer care is an unmet clinical need. Patients with baseline circulating tumour cell (BLCTCs) counts <5/7.5 mL represent a good prognosis subgroup but are non-evaluable for response assessment (decrease in CTCs). The aim of the study is to determine the value of any increase in CTCs (CTC progression) as an indicator of progression in prostate cancer patients with low pre-treatment CTCs (<5).

Patients and methods

We carried out a post hoc analysis of patients with BLCTCs < 5 treated in the COU-AA-301 (abiraterone or placebo + prednisone) and IMMC-38 (chemotherapy) trials. The association of CTC progression (increase in CTCs at 4, 8 or 12 weeks) with overall survival (OS) was evaluated in multi-variable Cox regression models. Performance of survival models with and without CTC progression was evaluated by calculating ROC curve area under the curves (AUCs) and weighted c-indices.

Results

Overall, 511 patients with CTCs < 5 (421 in COU-AA-301 and 90 in IMMC-38) were selected; 212 (41.7%) had CTC progression at 4, 8 or 12 weeks after treatment initiation. CTC progression was associated with significantly worse OS [27.1 versus 15.1 m; hazard ratio (HR) 3.4 (95% confidence interval [CI] 2.5-4.5; P < 0.001)], independent of baseline CTCs and established clinical variables. Adding CTC progression to the OS model significantly improved ROC AUC (0.77 versus 0.66; P < 0.001). Models including CTC progression had superior ROC AUC (0.77 versus 0.69; P < 0.001) and weighted c-index [0.750 versus 0.705; delta c-index: 0.045 (95% CI 0.019-0.071)] values than those including CTC conversion (increase to CTCs ≥ 5). In COU-AA-301, the impact of CTC progression was independent of treatment arm.

Conclusions

Increasing CTCs during the first 12 weeks of treatment are independently associated with worse OS from advanced prostate cancer in patients with baseline CTCs < 5 treated with abiraterone or chemotherapy and improve models with established prognostic variables. These findings must be prospectively validated.

Androgen receptor mutations in patients with castration-resistant prostate cancer treated with apalutamide

Background

Mutations in the androgen receptor (AR) ligand-binding domain (LBD), such as F877L and T878A, have been associated with resistance to next-generation AR-directed therapies. ARN-509-001 was a phase I/II study that evaluated apalutamide activity in castration-resistant prostate cancer (CRPC). Here, we evaluated the type and frequency of 11 relevant AR-LBD mutations in apalutamide-treated CRPC patients.

Patients and methods

Blood samples from men with nonmetastatic CRPC (nmCRPC) and metastatic CRPC (mCRPC) pre- or post-abiraterone acetate and prednisone (AAP) treatment (≥6 months' exposure) were evaluated at baseline and disease progression in trial ARN-509-001. Mutations were detected in circulating tumor DNA using a digital polymerase chain reaction-based method known as BEAMing (beads, emulsification, amplification and magnetics) (Sysmex Inostics' GmbH).

Results

Of the 97 total patients, 51 had nmCRPC, 25 had AAP-naïve mCRPC, and 21 had post-AAP mCRPC. Ninety-three were assessable for the mutation analysis at baseline and 82 of the 93 at progression. The overall frequency of detected AR mutations at baseline was 7/93 (7.5%) and at progression was 6/82 (7.3%). Three of the 82 (3.7%) mCRPC patients (2 AAP-naïve and 1 post-AAP) acquired AR F877L during apalutamide treatment. At baseline, 3 of the 93 (3.2%) post-AAP patients had detectable AR T878A, which was lost after apalutamide treatment in 1 patient who continued apalutamide treatment for 12 months.

Conclusions

The overall frequency of detected mutations at baseline (7.5%) and progression (7.3%) using the sensitive BEAMing assay was low, suggesting that, based on this assay, AR-LBD mutations such as F877L and T878A are not common contributors to de novo or acquired resistance to apalutamide.

ClinicalTrials.gov identifier

NCT01171898.

Collaborating to Compete: Blood Profiling Atlas in Cancer (BloodPAC) Consortium

The cancer community understands the value of blood profiling measurements in assessing and monitoring cancer. We describe an effort among academic, government, biotechnology, diagnostic, and pharmaceutical companies called the Blood Profiling Atlas in Cancer (BloodPAC) Project. BloodPAC will aggregate, make freely available, and harmonize for further analyses, raw datasets, relevant associated clinical data (e.g., clinical diagnosis, treatment history, and outcomes), and sample preparation and handling protocols to accelerate the development of blood profiling assays.

A prognostic index model for predicting overall survival in patients with metastatic castration-resistant prostate cancer treated with abiraterone acetate after docetaxel

A prognostic index model was developed, composed of six readily available and assessable factors and categorizing patients with metastatic castration-resistant prostate cancer treated with abiraterone–prednisone into distinct prognostic risk groups. This model could be useful for determining patient prognosis for follow-up, monitoring and patient stratification for clinical trials.

Background

Few prognostic models for overall survival (OS) are available for patients with metastatic castration-resistant prostate cancer (mCRPC) treated with recently approved agents. We developed a prognostic index model using readily available clinical and laboratory factors from a phase III trial of abiraterone acetate (hereafter abiraterone) in combination with prednisone in post-docetaxel mCRPC.

Patients and methods

Baseline data were available from 762 patients treated with abiraterone–prednisone. Factors were assessed for association with OS through a univariate Cox model and used in a multivariate Cox model with a stepwise procedure to identify those of significance. Data were validated using an independent, external, population-based cohort.

Results

Six risk factors individually associated with poor prognosis were included in the final model: lactate dehydrogenase > upper limit of normal (ULN) [hazard ratio (HR) = 2.31], Eastern Cooperative Oncology Group performance status of 2 (HR = 2.19), presence of liver metastases (HR = 2.00), albumin ≤4 g/dl (HR = 1.54), alkaline phosphatase > ULN (HR = 1.38) and time from start of initial androgen-deprivation therapy to start of treatment ≤36 months (HR = 1.30). Patients were categorized into good (n = 369, 46%), intermediate (n = 321, 40%) and poor (n = 107, 13%) prognosis groups based on the number of risk factors and relative HRs. The C-index was 0.70 ± 0.014. The model was validated by the external dataset (n = 286).

Conclusion

This analysis identified six factors used to model survival in mCRPC and categorized patients into three distinct risk groups. Prognostic stratification with this model could assist clinical practice decisions for follow-up and monitoring, and may aid in clinical trial design.

Trial registration numbers

NCT00638690.

Does Gleason score at initial diagnosis predict efficacy of abiraterone acetate therapy in patients with metastatic castration-resistant prostate cancer? An analysis of abiraterone acetate phase III trials

BACKGROUND

The usefulness of Gleason score (<8 or ≥8) at initial diagnosis as a predictive marker of response to abiraterone acetate (AA) plus prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC) was explored retrospectively.

PATIENTS AND METHODS

Initial diagnosis Gleason score was obtained in 1048 of 1195 (COU-AA-301, post-docetaxel) and 996 of 1088 (COU-AA-302, chemotherapy-naïve) patients treated with AA 1 g plus prednisone 5 mg twice daily by mouth or placebo plus prednisone. Efficacy end points included radiographic progression-free survival (rPFS) and overall survival (OS). Distributions and medians were estimated by Kaplan-Meier method and hazard ratio (HR) and 95% confidence interval (CI) by Cox model.

RESULTS

Baseline characteristics were similar across studies and treatment groups. Regardless of Gleason score, AA treatment significantly improved rPFS in post-docetaxel [Gleason score <8: median, 6.4 versus 5.5 months (HR = 0.70; 95% CI 0.56-0.86), P = 0.0009 and Gleason score ≥8: median, 5.6 versus 2.9 months (HR = 0.58; 95% CI 0.48-0.72), P < 0.0001] and chemotherapy-naïve patients [Gleason score <8: median, 16.5 versus 8.2 months (HR = 0.50; 95% CI 0.40-0.62), P < 0.0001 and Gleason score ≥8: median, 13.8 versus 8.2 months (HR = 0.61; 95% CI 0.49-0.76), P < 0.0001]. Clinical benefit of AA treatment was also observed for OS, prostate-specific antigen (PSA) response, objective response and time to PSA progression across studies and Gleason score subgroups.

CONCLUSION

OS and rPFS trends demonstrate AA treatment benefit in patients with pre- or post-chemotherapy mCRPC regardless of Gleason score at initial diagnosis. The initial diagnostic Gleason score in patients with mCRPC should not be considered in the decision to treat with AA, as tumour metastases may no longer reflect the histology at the time of diagnosis.

CLINICAL TRIALS NUMBER

COU-AA-301 (NCT00638690); COU-AA-302 (NCT00887198).

Management of patients with advanced prostate cancer: recommendations of the St Gallen Advanced Prostate Cancer Consensus Conference (APCCC) 2015

The first St Gallen Advanced Prostate Cancer Consensus Conference (APCCC) Expert Panel identified and reviewed the available evidence for the ten most important areas of controversy in advanced prostate cancer (APC) management. The successful registration of several drugs for castration-resistant prostate cancer and the recent studies of chemo-hormonal therapy in men with castration-naïve prostate cancer have led to considerable uncertainty as to the best treatment choices, sequence of treatment options and appropriate patient selection. Management recommendations based on expert opinion, and not based on a critical review of the available evidence, are presented. The various recommendations carried differing degrees of support, as reflected in the wording of the article text and in the detailed voting results recorded in supplementary Material, available at Annals of Oncology online. Detailed decisions on treatment as always will involve consideration of disease extent and location, prior treatments, host factors, patient preferences as well as logistical and economic constraints. Inclusion of men with APC in clinical trials should be encouraged.

Improved outcomes in elderly patients with metastatic castration-resistant prostate cancer treated with the androgen receptor inhibitor enzalutamide: results from the phase III AFFIRM trial

BACKGROUND

The randomized, double-blind phase III AFFIRM trial demonstrated that enzalutamide, an oral androgen receptor inhibitor, significantly prolonged overall survival (OS) [median 18.4 versus 13.6 months (hazard ratio, HR) 0.63 (95% confidence interval, CI, 0.53-0.75); P<0.001] compared with placebo in patients with metastatic castration-resistant prostate cancer who received prior docetaxel chemotherapy.

PATIENTS AND METHODS

A post hoc analysis was carried out to assess the efficacy and safety of enzalutamide on outcomes in younger (<75 years) and elderly (≥75 years) patients in the AFFIRM population. Statistics are presented by age group (<75 years, ≥75 years) for efficacy outcomes of OS, radiographic progression-free survival (rPFS), time to prostate-specific antigen (PSA) progression, PSA response, and safety.

RESULTS

OS was significantly improved with enzalutamide over placebo in patients<75 years [median not yet reached versus 13.6 months; HR 0.63 (95% CI 0.52-0.78), P<0.001] and in patients ≥75 years [median 18.2 versus 13.3 months; HR 0.61 (95% CI 0.43-0.86), P=0.004], respectively. rPFS was similarly improved in both the younger [HR 0.45 (95% CI 0.38-0.53), P<0.001] and elderly patient cohorts [HR 0.27 (95% CI 0.20-0.37), P<0.001] relative to placebo, as were time to PSA progression and PSA response. Adverse events (AEs) were similar between the two enzalutamide age groups, with the exception of an increase in patients≥75 years in the rates of all grade peripheral edema (22.1% versus 12.5%), fatigue (39.7% versus 31.6%), and diarrhea (26.6% versus 19.6%). The overall grade≥3 AE rates were low with no major difference in frequency or severity between age groups or treatment arms. Five patients were reported with seizure events; three patients<75 years and two patients ≥75 years.

CONCLUSIONS

Enzalutamide significantly improves outcomes in both younger (<75 years) and elderly patients (≥75 years), with comparable safety and tolerability.

Enzalutamide: Development from bench to bedside

Prostate tissue, whether benign or malignant, is heavily dependent on androgen receptor (AR) signaling for growth and proliferation. Androgen deprivation therapy has been standard of care for management of metastatic prostate cancer for the past 70 years. AR antagonists were developed to further abrogate signaling through this pathway by competitive inhibition of the receptor. First-generation compounds such as bicalutamide had modest efficacy, and in the setting of AR overexpression or specific mutations in the AR ligand-binding domain, these early compounds had partial agonist properties that could stimulate tumor growth. Enzalutamide was developed to overcome these deficiencies, and here, we present the story of its preclinical discovery, clinical development, and ultimate approval as a standard-of-care therapy for castration-resistant prostate cancer. Also discussed are ongoing efforts to elucidate mechanisms of resistance to this agent as well as studies that are investigating its role in other prostate cancer disease states and other cancer types.

Androgen dynamics and serum PSA in patients treated with abiraterone acetate

Background:

We analyzed the potential of abiraterone acetate (henceforth abiraterone) to reduce androgen levels below lower limits of quantification (LLOQ) and explored the association with changes in PSA decline in metastatic castration-resistant prostate cancer (mCRPC) patients.

Methods:

COU-AA-301 is a 2:1 randomized, double-blind, placebo-controlled study comparing abiraterone (1000 mg q.d.) plus low-dose prednisone (5 mg b.i.d.) with placebo plus prednisone in mCRPC patients post docetaxel. Serum testosterone, androstenedione and dehydroepiandrosterone sulfate from baseline to week 12 were measured by novel ultrasensitive two-dimensional liquid chromatography coupled to tandem mass spectrometry assays in a subset of subjects in each arm (abiraterone plus prednisone, n=80; prednisone, n=38). The association between PSA response (⩽50% baseline) and undetectable androgens (week 12 androgen level below LLOQ) was analyzed using logistic regression.

Results:

A significantly greater reduction in serum androgens was observed with abiraterone plus prednisone versus prednisone (all P⩽0.0003), reaching undetectable levels for testosterone (47.2% versus 0%, respectively). A positive association was observed between achieving undetectable serum androgens and PSA decline (testosterone: odds ratio=1.54; 95% confidence interval: 0.546–4.347). Reduction of androgens to undetectable levels did not occur in all patients achieving a PSA response, and a PSA response did not occur in all patients achieving undetectable androgen levels.

Conclusions:

Abiraterone plus prednisone significantly reduced serum androgens, as measured by ultrasensitive assays and was generally associated with PSA response. However, androgen decline did not uniformly predict PSA decline suggesting ligand-independent or other mechanisms for mCRPC progression.

Ipilimumab alone or in combination with radiotherapy in metastatic castration-resistant prostate cancer: results from an open-label, multicenter phase I/II study

BACKGROUND

This phase I/II study in patients with metastatic castration-resistant prostate cancer (mCRPC) explored ipilimumab as monotherapy and in combination with radiotherapy, based on the preclinical evidence of synergistic antitumor activity between anti-CTLA-4 antibody and radiotherapy.

PATIENTS AND METHODS

In dose escalation, 33 patients (≥6/cohort) received ipilimumab every 3 weeks × 4 doses at 3, 5, or 10 mg/kg or at 3 or 10 mg/kg + radiotherapy (8 Gy/lesion). The 10-mg/kg cohorts were expanded to 50 patients (ipilimumab monotherapy, 16; ipilimumab + radiotherapy, 34). Evaluations included adverse events (AEs), prostate-specific antigen (PSA) decline, and tumor response.

RESULTS

Common immune-related AEs (irAEs) among the 50 patients receiving 10 mg/kg ± radiotherapy were diarrhea (54%), colitis (22%), rash (32%), and pruritus (20%); grade 3/4 irAEs included colitis (16%) and hepatitis (10%). One treatment-related death (5 mg/kg group) occurred. Among patients receiving 10 mg/kg ± radiotherapy, eight had PSA declines of ≥50% (duration: 3-13+ months), one had complete response (duration: 11.3+ months), and six had stable disease (duration: 2.8-6.1 months).

CONCLUSIONS

In mCRPC patients, ipilimumab 10 mg/kg ± radiotherapy suggested clinical antitumor activity with disease control and manageable AEs. Two phase III trials in mCRPC patients evaluating ipilimumab 10 mg/kg ± radiotherapy are ongoing. ClinicalTrials.gov identifier: NCT00323882.

Effect of abiraterone acetate on fatigue in patients with metastatic castration-resistant prostate cancer after docetaxel chemotherapy

BACKGROUND

Fatigue is a common, debilitating side-effect of prostate cancer and its treatment. Patient-reported fatigue was evaluated as part of COU-AA-301, a randomized, placebo-controlled, phase III trial of abiraterone acetate and prednisone versus placebo and prednisone in metastatic castration-resistant prostate cancer (mCRPC) patients after docetaxel chemotherapy. This is the first phase III study in advanced prostate cancer to evaluate fatigue outcomes using a validated fatigue-specific instrument.

PATIENTS AND METHODS

The Brief Fatigue Inventory (BFI) questionnaire was used to measure patient-reported fatigue intensity and fatigue interference with activities of daily life. All analyses were conducted using prespecified responder definitions of clinically meaningful changes.

RESULTS

A total of 797 patients were randomized to abiraterone acetate and prednisone, and 398 were randomized to placebo and prednisone. Compared with prednisone alone, in patients with clinically significant fatigue at baseline, abiraterone acetate and prednisone significantly increased the proportion of patients reporting improvement in fatigue intensity (58.1% versus 40.3%, P = 0.0001), improved fatigue interference (55.0% versus 38.0%, P = 0.0075), and accelerated improvement in fatigue intensity (median 59 days versus 194 days, P = 0.0155).

CONCLUSIONS

In patients with mCRPC progressing after docetaxel chemotherapy, abiraterone acetate and prednisone yielded clinically meaningful improvements in patient-reported fatigue compared with prednisone alone.

Reversal of the low-affinity neurotrophin receptor stromal-epithelial expression pattern between benign and malignant human prostate

Reduced expression of the low-affinity p75 neurotrophin receptor (p75(NTR)) occurs in prostate epithelial cells during malignant transformation. Recent studies indicating that the p75(NTR) can transduce signals that induce apoptosis suggest that diminished p75(NTR) in transformed prostate cells may contribute to immortalization. Mutations in the transmembrane domain of the p75(NTR) gene have been associated with decreased p75(NTR) protein expression and may block the ability of the p75(NTR) to induce apoptosis. Therefore, we used Western blot to analyze prostate cancer (PC) cell lines for p75(NTR) protein expression and gene single strand conformation polymorphism (SSCP) analysis and direct DNA sequencing to analyze mutations in the transmembrane domain of the p75(NTR). p75(NTR) Protein was present in all cell lines, and mutations in the p75(NTR) gene were not detected in cDNA derived from any cell line. To define the expression pattern of p75(NTR) in PCs in vivo, we used immunohistochemical techniques to examine tissue specimens from 20 benign, 19 malignant primary, and 14 metastatic prostate specimens. In benign prostate tissues, expression of p75(NTR) was universally detected in basal cells but not in secretory epithelial or stromal cells. In both primary and metastatic PC tissues, p75(NTR) immunoreactivity could not be detected in malignant prostate epithelial cells. However, in contrast to the benign prostate, p75(NTR) protein was expressed in stromal cells surrounding malignant epithelial cells. Stromal p75(NTR) expression was present in 84% (16 of 19) primary and in 86% (12 of 14) metastatic specimens. These data show that in the benign prostate p75(NTR) protein is expressed by basal cells and not stromal cells whereas in malignant prostate p75(NTR) protein is expressed by stromal cells but not prostatic carcinoma cells. Reversal of the p75(NTR) stromal-epithelial pattern of expression between benign and malignant prostate suggests that p75(NTR) may contribute to the development and maintenance of prostate cancer.

A phase I/IIA study of AGS-PSCA for castration-resistant prostate cancer

BACKGROUND

This first-in-human phase I/IIA study was designed to evaluate the safety and pharmacokinetics (PKs) of AGS-PSCA a fully human monoclonal antibody directed to prostate stem cell antigen (PSCA) in progressive castration-resistant prostate cancer.

PATIENTS AND METHODS

Twenty-nine patients were administered infusions of AGS-PSCA (1-40 mg/kg) every 3 weeks for 12 weeks; 18 final patients received a 40-mg/kg loading dose followed by 20-mg/kg repeat doses. Primary end points were safety and PK. Immunogenicity, antitumor activity and circulating tumor cells were also evaluated.

RESULTS

No drug-related serious adverse events were noted. Dose escalation stopped before reaching the maximum tolerated dose as target concentrations were achieved. Drug levels accumulated linearly with dose and the mean terminal half-life was 2-3 weeks across dose levels. The 40-mg/kg loading dose followed by repeated 20-mg/kg doses yielded serum drug concentrations above the projected minimum therapeutic threshold after two to three doses without excessive drug accumulation or toxicity. Significant antitumor effects were not seen.

CONCLUSIONS

A 40-mg/kg loading dose followed by 20-mg/kg infusions every 3 weeks is the recommended phase II dose of AGS-PSCA. PSCA is a promising drug target and studies in prostate and other relevant solid tumors are planned.

Evaluation of circulating tumor cell (CTC) enumeration as an efficacy response biomarker of overall survival (OS) in metastatic castration-resistant prostate cancer (mCRPC): Planned final analysis (FA) of COU-AA-301, a randomized, double-blind, placebo-controlled, phase III study of abiraterone acetate (AA) plus low-dose prednisone (P) post docetaxel

LBA4517

Background: A preplanned interim analysis of COU-AA-301 showed that AA, a selective androgen biosynthesis (CYP17) inhibitor, significantly improves OS in mCRPC. This is the first phase III study to prospectively assess CTC as a surrogate biomarker as part of a regulatory qualification process, here using updated OS data. Methods: 1,195 patients (pts) with mCRPC post docetaxel were randomized 2:1 to AA (1 g QD) + P (5 mg BID) (n = 797) or placebo + P (n = 398). CTCs (screening and baseline [BL]; post BL at weeks 4, 8 and 12) were enumerated (cells/7.5 mL) at MSKCC and The ICR using CellSearch and analyzed with other prognostic covariates as dichotomous and continuous variables using updated OS data at 775 events (prior to crossover from placebo to AA). CTC (as part of a biomarker panel - LDH, PSA, Hg, AlkPhos) was examined as a surrogate for OS. Multivariate (Cox model) analyses were conducted. Results: At median follow up (FU) of 20.2 mo, the difference in median OS between the 2 groups improved from 3.9 to 4.6 mo (AA 15.8 mo vs placebo 11.2 mo; HR = 0.74; p < .0001). CTC counts were evaluated in 972 pts at screening and BL, 838 at 4 wks, 783 at 8 wks and 723 pts at 12 wks. High concordance between screening and BL values was observed (r = 0.83). CTC conversion using standard definition for unfavorable (CTC ≥ 5) and favorable (CTC < 5) counts was predictive of OS as early as 4 wks after treatment and its inclusion significantly reduced the treatment effect at all post-treatment time points (HR: from 0.74 to 0.97). A reduced model incorporating CTCs and LDH was developed. Conclusions: The magnitude of the treatment effect of AA on OS increased with longer FU. Using standard definition of CTC conversion, the biomarker panel demonstrated a level of surrogacy for OS by correlating well with survival and in a model-adjusted analysis dramatically attenuating the treatment effect. BL CTCs and CTC conversion, along with LDH, were key predictors of OS. Future trials will further evaluate the CTC-based surrogate developed from COU-AA-301.

Genomic analysis of circulating tumor cells to evaluate predictive biomarkers

38

Background: To estimate the association between molecular biomarkers detected in circulating tumor cells (CTC) and tumor sensitivity to treatment, robust assays are needed before qualification in prospective clinical trials.

Methods: To address the limitations of the current FDA cleared technology, we focused on improving our ability to isolate more purified CTC populations based on fluorescence-activated cell sorting (FACS) to capture EpCAM+, CD45−, DAPI− cells from patients with castration-resistant prostate cancer (CRPC). Androgen receptor (AR) and genes frequently mutated in CRPC have been selected from the integrative genomic profiling at MSK. We optimized the RainDance microfluidic PCR followed by targeted sequencing in low number of cancer cells, before proceeding to clinical samples.

Results: On blood samples from124 patients with progressive CRPC, FACS method isolates an average 100-fold more EpCAM+ events compared to the current FDA cleared CellSearch assay. By FACS, >10 or >50 events were isolated in 88% or 58% of patients, compared to 32% or 10% of patients by CellSearch, respectively. FACS isolated cells express prostate-specific mRNAs (PSA, AR, TMPRSS2-ERG), as detected by an analytically validated multiplex RT-PCR, indicating that these EpCAM+ events are bona fide CTC. For genomic profiling, sufficient high quality DNA was obtained from as little as 50 CTC, with a recovery rate of 89% from FACS sorted samples and adequate sequencing coverage, and 1:4 detection threshold in a heterogeneous cell population. Selected missense mutations in AR, PIK3CA and TP53 found in CTC but not in WBC from same patient are further analyzed.

Conclusions: Molecular alterations in CTC can potentially serve as predictive markers of sensitivity and clinical outcomes as surrogate tissue in clinical practice. We established standard operating procedures for specimen processing, and confirmed the sequencing coverage and polymorphism detection thresholds in a heterogeneous cell population. In the context of available samples collected from patients enrolled on AR-targeted therapies, we will generate data to qualify CTC as biomarkers under the Oncology Biomarker Qualification Initiative.

[Table: see text]

Improved survival outcomes in clinically relevant patient subgroups from COU-AA-301, a phase III study of abiraterone acetate (AA) plus prednisone (P) in patients with metastatic castration-resistant prostate cancer (mCRPC) progressing after docetaxel-based chemotherapy

4

Background: AA is a selective androgen biosynthesis inhibitor that blocks the action of CYP17. Preclinical and early clinical studies suggest that AA potently inhibits persistent androgen synthesis from adrenal and intratumoral sources, thus suppressing an important growth stimulus for mCRPC.

Methods: COU-AA-301 ( NCT00638690 ) is an international, randomized, double blind study of AA (1,000 mg + P 5 mg po BID) vs placebo + P administered to men with mCRPC progressing after docetaxel-based chemo. OS is the primary endpoint. Patients treated with previous ketoconazole or > 2 prior chemo regimens were excluded.

Results: Data are drawn from a planned, stratified interim analysis, unblinded in August 2010, based on significant OS improvement in the AA + P treatment group compared to the placebo + P group [median OS 14.8 vs.10.9 months; HR = 0.646 (0.54-0.77), P < 0.0001]. A subgroup analysis for OS is presented in the table. Mineralocorticoid- related AEs were more common in the AA arm vs placebo: fluid retention 30.5% vs 22.3%, hypokalemia 17.1% vs 8.4%; but grade 3/4 hypokalemia (3.8% vs 0.8%), and grade 3/4 hypertension (1.3% vs 0.3%) were infrequent. LFT abnormalities were observed in 10.4% AA vs 8.1% placebo; and cardiac disorders were observed in 13.3% AA vs 10.4% placebo.

Conclusions: AA significantly prolongs OS in patients with mCRPC who have progressed after docetaxel-based chemo. AA's favorable treatment effect on OS, observed across multiple patient subgroups (HR range 0.59 – 0.74 vs placebo + P), was consistent with the survival benefit for the overall study population.

[Table: see text]

[Table: see text]

A phase I dose escalation trial of vaccine replicon particles (VRP) expressing prostate-specific membrane antigen (PSMA) in patients (pts) with castration-resistant prostate cancer (CRPC): Preliminary results

140

Background: Prostate-specific membrane antigen (PSMA), a type II transmembrane protein overexpressed in prostate cells as they emerge into the androgen-independent state, remains a target to which vaccines with novel adjuvants or naked DNA has been directed. The PSMA-Viral Replicon Package (VRP) is a propagation-defective vector system from an attentuated strain of an alpha virus (VEE) encoding PSMA for use as a vaccine in prostate cancer. The PSMA gene is encoded by a subgenomic messenger RNA (mRNA), leading to high level expression of PSMA protein and presentation to the immune system.. We report preliminary results of a first in human trial using PSMA VRP to elicit immune responses targeting PSMA.

Methods: Up to 18 pts with chemotherapy naïve CRPC metastatic to bone or soft tissue were permitted with 12 pts enrolled with ECOG status of 0 or 1. PSMA VRP was administered SC doses of either 0.9×107 IU or 0.36×108 IU for a total of 5 doses given on weeks 1, 4, 7, 10 and 18. Adverse events, PSA, circulating tumor cells, and clinical disease progression were assessed. Immune assessment was performed on patients' sera by ELISA and flow cytometry of serum binding to PSMA expressing tumor cells (3T3) and cellular (IFN-g EliSpot) components. Patients underwent imaging with bone and CAT scans every 3 months.

Results: Three pts received 0.9×107 IU and 9 received 0.36×108 IU. Of these, 8 pts received all 5 vaccines. Four pts were taken off study for disease progression. One pt at the 0.36×108 continues on study and will be receiving his seventh vaccine. The demographic featuresof the 12 subjects enrolled were similar (mean age 69±11 yrs). No significant adverse events were noted; no aberrant laboratory abnormalities were associated with treatment. Weak humoral responses were observed in 1 patient in the 0.9×107 IU group and in 3 treated at 0.36×108.

Conclusions: In this first-in-man evaluation, vaccination with PSMA VRP appeared to be well-tolerated but does not appear to show impact on disease progression. Further studies are ongoing to assess immune responses and identify potential pathways for enhancement of the PSMA VRP approach.

[Table: see text]

Antitumor activity of MDV3100 in pre- and post-docetaxel advanced prostate cancer: Long-term follow-up of a phase I/II study

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Background: MDV3100 is a novel androgen receptor (AR) antagonist selected for potent AR activity and devoid of partial agonist effects. A preliminary report of the phase I/II study described anti-tumor activity and adverse events (Scher HI et al. Lancet. 2010;375:1437). This abstract provides long-term follow-up on time to PSA and radiographic progression in this trial.

Methods: Patients (pts) with progressive castration resistant prostate cancer (CRPC) were enrolled in sequential cohorts of 3-6 pts at MDV3100 doses of 30, 60, 150, 240, 360, 480 and 600 mg/day. Once the tolerability of a dose was established, enrollment was expanded at doses ≥60 mg/day to include approximately 12 chemotherapy naïve (naïve) pts and 12 pts previously treated with docetaxel (post-chemo) per cohort.

Results: 140 pts were enrolled of which 18 (13%) pts continue on active treatment (16 naive and 2 post-chemo). The median time on treatment is 51 weeks for naïve and 17 weeks for post-chemo groups. Median time on treatment for the 18 patients still on study is 131 weeks. The median time to PSA progression, defined per-protocol as a ≥25% increase in PSA from baseline, was not met for naïve and was 33 weeks for post-chemo groups. Median time to PSA progression by Prostate Cancer Clinical Trials Working Group 2 criteria was 41 weeks for naïve and 20 weeks for post-chemo groups. Median time to radiographic progression was 56 weeks for naive and 24 weeks for post-chemo groups. Circulating tumor cell counts available for 128 of 140 pts showed 91% (70/77) with favorable pre-treatment counts (<5 cells/7.5 mL blood) remaining favorable post-treatment, while 49% (25/51) converted from unfavorable pre-treatment to favorable post-treatment.

Conclusions: MDV3100 demonstrates durable anti-tumor activity in pts with CRPC both before and after chemotherapy. Based on these promising results MDV3100 is currently being evaluated in two global phase III studies in pts with metastatic CRPC, the AFFIRM study in pts previously treated with docetaxel and the PREVAIL study in chemotherapy-naïve pts who have progressed on androgen deprivation therapy.

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Pain and analgesic use in men with metastatic prostate cancer

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Background: Pain is an important endpoint in metastatic prostate cancer and was the basis for the 1996 FDA approval of mitoxantrone. Standards for pain assessment have evolved, and a 2006 draft FDA guidance provides new recommendations for patient- reported outcomes. Contemporary palliation models generally require pain reduction starting from baseline worst pain scores of ≥4/10, and progression models require a sufficient proportion of patients’ pain scores to worsen in order to assure an adequate effect size. The prevalence and distribution of pain severity at specific points in the prostate cancer disease continuum are not well defined. Consequently, it is unclear if sufficient numbers of patients are available to conduct prospective studies using pain palliation or prevention as primary endpoints. Methods: A questionnaire that includes the Brief Pain Inventory and additional pain/analgesia items was developed as a collaboration between the DOD/PCF-supported Prostate Cancer Clinical Trials Consortium (PCCTC) and FDA Study Endpoints and Labeling Design (SEALD) team. IRB waivers were obtained for anonymous administration at 5 PCCTC institutions (Sloan-Kettering, Duke, Johns Hopkins, Anderson, OHSU). Administration is ongoing. Results: Between August-December 2008, 325 men with prostate cancers representing different disease states being seen in outpatient clinics of participating centers were each queried once. Median age was 70 (range 49–87). More than half (n=175) self-reported metastatic disease, including 129 with bone metastases. Among those with bone metastases, 76 (59%) reported experiencing any level of pain in the last week; 49 (38%) reported a worst pain score ≥4/10 of which 38 (78%) used analgesics over the past week and 31 (63%) used daily analgesia. In addition, 70 of the 76 (92%) noted that their pain interfered with work, sleep, or enjoyment of life, with 25 (33%) noting severe interference. Among the 49 patients with pain scores ≥4/10, current or past docetaxel use was reported by 32 (65%), androgen deprivation therapy by 47 (96%), and 28 (57%) had been or were currently enrolled in a clinical trial. Conclusions: Pain is sufficiently prevalent in men with metastatic prostate cancer to enable prospective assessment of palliation endpoints in clinical trials.

No significant financial relationships to disclose.