FORMULA-509: A Multicenter Randomized Trial of Post-Operative Salvage Radiotherapy (SRT) and 6 Months of GnRH Agonist with Either Bicalutamide or Abiraterone Acetate/Prednisone (AAP) and Apalutamide (Apa) Post-Radical Prostatectomy (RP)

PURPOSE/OBJECTIVE(S)

FORMULA-509 was designed to evaluate whether adding six months of AAP and Apa to a GnRH Agonist could improve outcomes compared to six months of bicalutamide plus GnRH Agonist for patients with unfavorable features receiving SRT for a detectable PSA post-RP.

MATERIALS/METHODS

FORMULA-509 is an investigator-initiated, multi-center, open-label, randomized trial. Patients had PSA ≥0.1 post-RP and one or more unfavorable features (Gleason 8-10, PSA >0.5, pT3/T4, pN1 or radiographic N1, PSA doubling time <10 months, negative margins, persistent PSA, gross local/regional disease, or Decipher High Risk). All patients received SRT plus 6 months of GnRH agonist and randomization was to concurrent bicalutamide 50 mg or AAP 1000 mg/5 mg + Apa 240 mg QD. Radiation to pelvic nodes was required for pN1 and optional for pN0. The primary endpoint was PSA progression-free survival (PFS) and secondary endpoint was metastasis-free survival (MFS) determined by conventional imaging. The study was powered to detect a HR of 0.50 for PFS and a HR of 0.30 for MFS, each with 80% power and one-sided type I error of 0.05. Stratification was by PSA at study entry (>0.5 vs.≤0.5) and pN0 vs pN1. Analyses within these subgroups were pre-planned and utilized two-sided p-values.

RESULTS

Three hundred forty-five participants (332 evaluable) from 9 sites were randomized from 11/24/2017 to 3/25/2020 (172 bicalutamide, 173 AAP/Apa). Median follow-up was 34 (6-53) months; 29% were pN1 and 31% had PSA >0.5 ng/mL. The HR for PFS was 0.71 (90% CI 0.49-1.03), stratified one-sided log-rank p = 0.06 (3-year PFS was 68.5% bicalutamide vs 74.9% AAP/Apa). The HR for MFS was 0.57 (90% CI 0.33-1.01), stratified one-sided log rank p = 0.05 (3-year MFS was 87.2% bicalutamide vs 90.6% AAP/Apa). In a pre-planned analysis by stratification factors, AAP/Apa was significantly superior for patients with PSA >0.5 for PFS [HR 0.50, (95% CI 0.27-0.95), p = 0.03 (2-sided); 3-year PFS 46.8% bicalutamide vs. 67.2% AAP/Apa] and for MFS [HR 0.32 (95% CI 0.13-0.84), p = 0.02 (2-sided); 3-year MFS 66.1% bicalutamide vs. 84.3% AAP/Apa.] No statistically significant benefit was detected in pre-planned analyses of stratification subgroups defined by PSA≤0.5, pN0, or pN1. Adverse events were consistent with the known safety profiles of the agents being studied, with more rash and hypertension in the AAP/Apa arm.

CONCLUSION

Although this primary analysis did not meet the pre-specified threshold for statistical significance, it does strongly suggest that the addition of AAP/Apa instead of bicalutamide to SRT+6 months of GnRH Agonist may improve PFS and MFS, particularly in the subgroup of patients with PSA>0.5 where a pre-planned subgroup analysis by stratification factors observed a statistically significant benefit for both PFS and MFS. (NCT03141671).

Radiographic progression with nonrising PSA in metastatic castration-resistant prostate cancer: post hoc analysis of PREVAIL

BACKGROUND

Advanced prostate cancer is a phenotypically diverse disease that evolves through multiple clinical courses. PSA level is the most widely used parameter for disease monitoring, but it has well-recognized limitations. Unlike in clinical trials, in practice, clinicians may rely on PSA monitoring alone to determine disease status on therapy. This approach has not been adequately tested.

METHODS

Chemotherapy-naive asymptomatic or mildly symptomatic men (n=872) with metastatic castration-resistant prostate cancer (mCRPC) who were treated with the androgen receptor inhibitor enzalutamide in the PREVAIL study were analyzed post hoc for rising versus nonrising PSA (empirically defined as >1.05 vs ⩽1.05 times the PSA level from 3 months earlier) at the time of radiographic progression. Clinical characteristics and disease outcomes were compared between the rising and nonrising PSA groups.

RESULTS

Of 265 PREVAIL patients with radiographic progression and evaluable PSA levels on the enzalutamide arm, nearly one-quarter had a nonrising PSA. Median progression-free survival in this cohort was 8.3 months versus 11.1 months in the rising PSA cohort (hazard ratio 1.68; 95% confidence interval 1.26-2.23); overall survival was similar between the two groups, although less than half of patients in either group were still at risk at 24 months. Baseline clinical characteristics of the two groups were similar.

CONCLUSIONS

Non-rising PSA at radiographic progression is a common phenomenon in mCRPC patients treated with enzalutamide. As restaging in advanced prostate cancer patients is often guided by increases in PSA levels, our results demonstrate that disease progression on enzalutamide can occur without rising PSA levels. Therefore, a disease monitoring strategy that includes imaging not entirely reliant on serial serum PSA measurement may more accurately identify disease progression.

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.

Circulating tumor cells (CTC) in patients with metastatic castration-resistant prostate cancer (CRPC) receiving abiraterone acetate (AA) after failure of docetaxel-based chemotherapy

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Background: Selecting targeted therapies and assessing outcome in patients (pts) with CRPC are significant unmet medical needs. A proportion of CRPC remain dependent on androgen receptor (AR) activation. AA inhibits CYP17 to decrease serum androgen to undetectable levels. Methods: AA (1000 mg QD oral) was studied in pts with metastatic CRPC who had progressed on docetaxel based chemotherapy. The primary endpoint was a >50% decline in PSA from baseline. We monitored changes in CTC number with therapy, and performed FISH for AR in CTC as previously described. Results: At MSKCC, 54 pts were screened and 48 treated; 38 pts received prednisone from the start of treatment. The median (IQR) age was 70 yrs (63–79), PSA 99.9 ng/mL (36.4–343), and CTC were 17 (4–49) per 7.5 ml of blood at baseline. Prior systemic therapy included > 3 hormonal therapies in 63%; while 71% received 1, 29% had 2 lines of chemotherapy. Metastatic sites were bone alone in 10 pts (21%), bone and lymph nodes in 21 (44%), 15 (31%) with visceral disease, 2 with soft tissue alone. Baseline CTC count was > 5 in 35 pts, whereas 13 pts had <5; CTC changes with treatment are presented in table below. Pts in Group A were treated on protocol for a median of 8.9 m, compared to 2.8 m in group B (P <0.001). Among pts with baseline CTC > 5, the CTC decline to <5 was associated with a decline in PSA by >50% (p< 0.001). From 28 pts with FISH in CTC, 13 (47%) pts had AR amplification, 8 (29%) pts had copy number gain, and 5 (10%) pts had no evident AR copy number abnormalities; FISH failed in 2 pts. PSA declined > 50% in 5 (38%) pts with AR amplification, 2 (25%) pts with gain, and 4 (80%) pts without AR abnormalities. Conclusions: Changes in CTC with treatment may represent valuable intermediary endpoints for clinical benefit. We are prospectively testing pre and post-therapy CTC, and separately AR FISH profiles and clinical outcomes in COU-AA-301, a phase III trial for CRPC patients who have received docetaxel based chemotherapy.

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Phase I/II study of docetaxel and 153Sm for castrate metastatic prostate cancer (CMPC): Summary of dose-escalation cohorts and first report on the expansion cohort

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Background: We previously reported (ASCO 2008) that full doses of docetaxel (Tax) and Sm can be repetitively delivered safely using a schedule of q 3 week (wk) Tax and q 6–9 wk Sm. Here we summarize the dose-escalation cohorts and safety/efficacy data from the expansion cohort of 24 pts. Methods: Cohorts of 3–6 pts with CPMC were defined by: 65, 70, 75, 75, 75 mg/m2 of Tax and Sam 0.5, 0.5, 0.5, 0.75, 1 mCi/kg. Each cycle was 6 wks. The expansion cohort used 75 mg/m2 Tax (q 3 wk) and 1 mCi/kg Sm (q 9 wk). Pts with an ANC of grade 0–1 and platelet count of > 100,000/mm3 at the end of cycle 1 received additional cycles until progression or toxicity. Results: 52 pts have been treated. 28 pts were taxane naïve, 11 received previous taxanes but were not refractory, and 13 were taxane refractory. As anticipated, side effects were primarily hematologic. However, the leading cause for treatment termination was disease progression, involving 16/52 (31%) pts, rather than toxicity. 12/52 (23%) pts came off for thrombocytopenia, and 2/52 (4%) pts experienced neutropenic fever. Cohort 3 tolerated the highest cumulative dose and total number of doses of docetaxel (mean of 8 doses, range 4–12; mean total dose 600 mg/m2, range 300–900 mg/m2). Cohort 5 tolerated the highest exposure to Sm (mean of 3 doses, range 1–5). 50 pts are evaluable for response; 22 (44%) achieved a ≥ 50% decline in PSA. 50% of the taxane naïve patients achieved a significant PSA decline, as did 55% of the taxane exposed, and 23% of the taxane refractory pts. Mean time to progression in the taxane naïve, treated, and refractory groups were: 7.5 (range 1.4–22.6), 5.8 (range 0.7–13.7), and 4.3 (range 0.7–11.2) months. Conclusions: This regimen is safe and appears to be active both in taxane naïve and taxane refractory patients, as reflected by favorable toxicity profiles, and rates of significant PSA declines and times to progression. The optimal phase II dose may differ by the population treated. For studies involving taxane naïve patients, the regimen of cohort 3 maximizes docetaxel exposure; for studies of taxane refractory patients, cohort 5 maximizes Sm exposure. Support: EUSA, NIH CA102544.

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Phase I dose-finding study of weekly docetaxel followed by flavopiridol for patients with advanced solid tumors

PURPOSE

Flavopiridol is a cyclin-dependent kinase inhibitor that enhances docetaxel-induced apoptosis in a sequence-specific manner. In vivo, docetaxel must precede flavopiridol by at least 4 h to induce this effect. We conducted a phase I trial of weekly, sequential docetaxel followed 4 h later by flavopiridol in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Docetaxel at a fixed dose of 35 mg/m2 was administered over 30 min, followed 4 h later by escalating doses of flavopiridol, ranging from 20 to 80 mg/m2 in successive cohorts, administered weekly over 1 h. This schedule was repeated for 3 weeks of each 4-week cycle.

RESULTS

Twenty-seven evaluable patients were enrolled. The combination was well tolerated, with one dose-limiting toxicity occurring at flavopiridol 70 mg/m2 (grade 3 mucositis) and one dose-limiting toxicity at 80 mg/m2 (grade 4 neutropenia). We observed 1 complete response in a patient with pancreatic carcinoma and 4 partial responses in pancreatic (1), breast (2), and ovarian (1) cancer patients. Stable disease was seen in 10 patients. Pharmacokinetic studies showed Cmax ranging from 1.49 +/- 0.69 micromol/L (flavopiridol 20 mg/m2) to 4.54 +/- 0.08 micromol/L (flavopiridol 60 mg/m2) in cycle 1.

CONCLUSIONS

Treatment with weekly, sequential docetaxel followed by flavopiridol is an effective and safe regimen at all flavopiridol dose levels. The pharmacokinetic data indicate that concentrations of flavopiridol that enhance the effects of docetaxel both in vitro and in vivo can be achieved. Clinical activity is encouraging, even in patients who have received a prior taxane and in patients with gemcitabine-refractory metastatic pancreatic cancer.

Suberoylanilide hydroxamic acid (vorinostat) post chemotherapy in hormone refractory prostate cancer (HRPC) patients (pts): A phase II trial by the Prostate Cancer Clinical Trials Consortium (NCI 6862)

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Background: Histone deacetylases (HDACs) are key regulators of histone acetylation status, which is critical to expression of genes implicated in the regulation of cell survival, proliferation, differentiation and apoptosis. Vorinostat is a potent oral HDAC inhibitor with anti-tumor activity in PC models and in phase I clinical trials. A phase II trial is assessing vorinostat in HRPC pts. Methods: Eligible pts had disease progression on 1 prior chemotherapy for HRPC, a PSA of ≥ 5ng/ml, and adequate organ function. Vorinostat was administered orally at 400 mg daily in 21-day cycles. Response was assessed every 12 weeks. The primary endpoint is proportion of pts without progression at 6 months by objective and biochemical measures. This study is designed to accrue 29 pts (80% power at the 5% significance level to distinguish between a rate of 10% vs 30%). If ≥ 7/29 pts are progression-free at 6 months, the drug will be recommended for further study. Secondary endpoints include safety, rate of PSA decline, objective response rate and overall survival. Correlative studies assessing the effect of vorinostat on serum levels of IL-6, soluble IL-6 receptor and gp130 levels were conducted. Results: To date 23/29 pts have been accrued. Median age is 68 years (range 54–77), 70% had performance status 1 and 78% are white. At registration disease progression was defined by: PSA in 83%, bone in 74% and soft tissue in 43%. Median number of cycles is 2 (range 1–6), 57% of pts required at least 1 dose reduction. At time of this report 39% of pts remain on therapy. 19 pts are toxicity evaluable. Most common treatment related adverse events (AEs) were: fatigue (74%), anorexia (63%), nausea (58%), diarrhea (32%), dehydration, taste alteration and vomiting (26% each). There was 1 grade (G) 4 thrombosis and 11 pts had G 3 AEs, the most common were: fatigue (32%) and nausea and anorexia (11% each). 3/9 response evaluable pts achieved stable disease. Conclusions: Vorinostat is feasible post chemotherapy in pts with HRPC, however it is associated with significant toxicities requiring dose reductions. Final efficacy, safety and correlative studies will be reported. Support: CTEP, N01-CM-62201, PC051375, PC 051382

No significant financial relationships to disclose.

Phase I study of docetaxel and 153Sm repetitively administered for castrate metastatic prostate cancer (CMPC)

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Background: Docetaxel (Tax) prolongs survival in patients (pts) with CMPC. Early clinical data suggest that Tax combined with bone seeking radiopharmaceuticals may improve survival relative to chemotherapy alone. 153Sm-lexidronam (Sam) (Quadramet, Cytogen Inc.) is a radiopharmaceutical with a short T1/2 and a favorable toxicity profile. Methods: Pts with progressive CMPC are treated in cohorts of 3–6. Prior treatment with taxanes is permissible. Cohorts are defined by dose escalations of: Tax 65, 70, 75, 75, 75 mg/m2 and Sam 0.5, 0.5, 0.5, 0.75, 1 mCi/kg. Each cycle is 6 weeks. Tax is given day 1 and 22 and Sam day -1 to 1 of each cycle. DLT is defined as cycle 1 = grade 3 non-hematologic toxicity, grade 3 neutropenia that lasts for >29 days, or grade 3- 4 anemia or thrombocytopenia of = 5 days. Pts with an ANC of grade 0–1 or platelet count (PLT) of >100,000/mm3 at the end of cycle 1 may receive additional cycles. Pts are treated until progression or toxicity. Results: 18 pts have been treated in 5 cohorts of 3 pts to date. 6 pts were treated in cohort 2. Two pts have not yet received enough treatment to be evaluable. DLT has not yet been reached. The mean number of cycles/pt is 3 (range 1–6). As anticipated, toxicities have primarily been hematologic (see table ). Two pts came off study for hematologic toxicity; one in cohort 2 had grade 3 PLT after 5 cycles and has not recovered at >175 days and 1 pt (cohort 2) failed to recover PLT in the allotted time frame during cycle 4 prohibiting further treatment. No other pts required treatment delays for hematologic toxicity. Mean baseline PSA was 294.6ng/ml with 7/16 (44%) pts achieving = 50% decline in PSA. Conclusions: Coadministration of Tax and Sam has been well tolerated. Repetitive dosing is feasible. Standard approved doses of each drug are being tested in the present (and final) cohort. DLT has not yet been reached. Accrual continues, to refine the optimal dose and schedule in preparation for phase II. Support: Cytogen, Inc., NIH CA102544

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No significant financial relationships to disclose.