On October 3, 2022 Clovis Oncology, Inc. (NASDAQ: CLVS) reported positive top-line data from the Phase 3, open-label, multicenter, randomized TRITON3 trial demonstrating that Rubraca monotherapy treatment achieved the primary endpoint of significantly improved radiographic progression-free survival (rPFS) by independent radiology review (IRR) compared with the control group, which consisted of physician’s choice of docetaxel, abiraterone acetate, or enzalutamide (Press release, Clovis Oncology, OCT 3, 2022, View Source [SID1234621615]). Benefit was observed in both primary efficacy analyses of patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC): first, those who had mutations in BRCA, as well as all patients randomized in the trial, inclusive of mutations in BRCA or ATM (the overall intent-to-treat population (ITT)). The safety profile of Rubraca observed in the TRITON3 study was consistent with Rubraca labelling.
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During the first quarter of 2023, the Company plans to submit a supplemental New Drug Application (sNDA) to the FDA for the BRCA subgroup of patients and intends to discuss with the FDA submitting for the broader ITT population.
"We believe that the positive results from TRITON3 further demonstrate the important role that Rubraca can play as a treatment option for men with metastatic castration-resistant prostate cancer associated with homologous recombination deficiency, and we look forward to submitting these data to the regulatory authorities in the US during Q1 2023. Not only does this provide a potential treatment option for eligible men with earlier stage disease, but it is the first and only PARP inhibitor that has demonstrated superior radiographic PFS compared to chemotherapy, which is today the standard of care for these patients," said Patrick J. Mahaffy, President and CEO of Clovis Oncology. "Most importantly, I would like to thank the patients, physicians, and our colleagues whose commitment to this trial made these results possible, which now offer the potential to make a difference in the lives of many men with advanced prostate cancer."
"Men with this type of metastatic prostate cancer want to get their genetically targeted therapy as early as possible, and this trial clearly shows the value of rucaparib as a treatment for these men," said Alan H. Bryce, MD, chair of the Division of Hematology and Medical Oncology at the Mayo Clinic and principal investigator of the TRITON3 trial. "A key point is that rucaparib can replace chemotherapy in this setting. The current standard of care for these men is chemotherapy with docetaxel, and rucaparib is the only PARP inhibitor which has beaten a docetaxel-containing control arm in a clinical trial."
"This trial demonstrates the potential for rucaparib to treat men with early-stage metastatic castration-resistant prostate cancer," said Karim Fizazi, MD, PhD, medical oncologist at Gustave Roussy, and a full professor in Oncology at the University of Paris-Saclay and principal investigator of the TRITON3 trial. "To my knowledge, this is the first time in two decades that a potential new treatment, rucaparib, has shown in a randomized controlled trial radiographic PFS efficacy over an investigator’s choice control arm that included docetaxel chemotherapy, a long-standing standard of care for men with metastatic castration-resistant prostate cancer, and this is excellent news for patients."
TRITON3 is a Phase 3, multicenter, open-label, randomized trial of Rubraca in patients with chemotherapy-naïve mCRPC. The study enrolled 405 patients with a mutation in BRCA or ATM who were randomized to Rubraca or the control group, which consisted of physician’s choice of docetaxel, abiraterone acetate, or enzalutamide. Approximately 55% of the patients in the control arm received docetaxel. The primary endpoint was rPFS by IRR, in patients with mutations in BRCA1, BRCA2or ATM. TRITON3 was designed as a Phase 3 trial to confirm and expand the efficacy data from TRITON2 in an earlier treatment setting against a relevant control arm.
Patients were required to have disease progression after treatment with one prior next-generation AR-targeted therapy (abiraterone acetate, enzalutamide, apalutamide or investigational agent), as well as a deleterious mutation in BRCA or ATM. Following a protocol amendment, patients were permitted to have received a qualifying AR-targeted therapy in either the hormone-sensitive or castration-resistant setting, and as a result, approximately 18% of patients in TRITON3 had received prior AR-targeted therapy in the metastatic hormone-sensitive setting only.
The primary efficacy analysis evaluated two prospectively defined molecular sub-groups in a step-down manner: 1) the BRCA subgroup, and 2) all patients randomized (ITT) in TRITON3, inclusive of those with BRCA or ATM mutations.
Following is a summary of the primary efficacy analyses of rPFS by independent radiologic review (IRR), the primary analysis of TRITON3.
Significant Improvement in rPFS in the BRCA Patient Population
The Rubraca arm (n=201) achieved statistical significance over the control arm (n=101) for the primary endpoint of rPFS with a hazard ratio of 0.50 (95% CI: 0.36-0.69). The median PFS for the population of patients with BRCA mutations treated with Rubraca was 11.2 months vs 6.4 months among those who received physician’s choice (p<0.0001).
Significant Improvement in rPFS in the ITT population, inclusive of those with BRCA or ATM mutations
Rubraca also showed statistical significance in all 405 patients randomized in TRITON3. The Rubraca arm (n=270) successfully achieved statistical significance over the control arm (n=135) for the primary endpoint of rPFS with a hazard ratio of 0.61 (95% CI: 0.47-0.80). The median PFS for all patients enrolled in TRITON3 and treated with Rubraca was 10.2 months vs 6.4 months among those who received physician’s choice (p=0.0003).
rPFS in Exploratory ATM Mutation Subgroup
In the exploratory subgroup of men with tumor ATM mutations (n=103), the hazard ratio for rPFS was 0.97 (95% CI: 0.59-1.52). Median rPFS in the Rubraca arm (n=69) was 8.1 months vs 6.8 months in the control arm (n=34) with a nominal p-value (p=0.8421).
Secondary Endpoint of Overall Survival Summary
The hazard ratio for the interim analysis of the secondary endpoint of overall survival (OS) in the BRCA subgroup and ITT population, which are not yet mature, favored Rubraca. The hazard ratio for OS in the exploratory subgroup of ATM, which is mature, favored the control arm. The 95% confidence intervals for these OS analyses included less than one for the exploratory endpoint ATM, signifying no statistical difference in outcomes between Rubraca and control.
Summary of TRITON3 Safety
The safety profile of Rubraca observed in TRITON3 was consistent with Rubraca labelling.The most common (≥5%) treatment-emergent grade 3 or higher adverse events (TEAEs) among all patients treated with Rubraca in the TRITON3 study were anemia/decreased hemoglobin (23.7%), neutropenia/decreased neutrophil count (7.4%), asthenia/fatigue (7.0%), thrombocytopenia/decreased platelet count (5.9%) and increased ALT/AST (5.2%). The discontinuation rate for TEAEs was 14.8% for Rubraca-treated patients and 21.5% for the control arm.
Clovis Oncology will submit an expanded description of the TRITON3 results for presentation in a scientific session at the Prostate Cancer Foundation Annual Scientific Retreat later this month and plans to submit additional data to a medical meeting in early 2023.
Rubraca is not currently approved in the chemotherapy-naïve mCRPC setting.
About the TRITON3 Clinical Trial
TRITON3 (NCT02975934) is a Phase 3, multicenter, open-label, randomized trial of Rubraca in patients with chemotherapy-naïve mCRPC. Patients with a mutation in BRCA or ATM were randomized to Rubraca or the control group, which consisted of physician’s choice of docetaxel, abiraterone acetate, or enzalutamide. The primary objective was efficacy, as analysed by independent radiology review (IRR) of radiographic progression-free survival (rPFS) in patients with mutations in BRCA1, BRCA2 or ATM. TRITON3 was designed as a Phase 3 trial to confirm and expand the efficacy data from TRITON2 in an earlier treatment setting against a relevant control arm.
About Prostate Cancer
The American Cancer Society estimates that approximately 268,000 men in the US will be diagnosed with prostate cancer in 2022, and the GLOBOCAN Cancer Fact Sheets estimated that approximately 473,000 men in Europe were diagnosed with prostate cancer in 2020. Castrate-resistant prostate cancer has a high likelihood of developing metastases. Metastatic castrate-resistant prostate cancer (mCRPC) is an incurable disease, usually associated with poor prognosis.i Approximately 43,000 men in the US were expected to be diagnosed with mCRPC in 2020.ii According to the National Cancer Institute, the five-year survival rate for mCRPC is approximately 30%. BRCA or ATM mutations have been detected in approximately 19% of patients with mCRPC according to articles published in JCO Precision Oncology in 2017 and in Clinical Cancer Research in 2021. These molecular markers may be used to select patients for treatment with a PARP inhibitor.iii
About Rubraca (rucaparib)
Rubraca is an oral, small molecule inhibitor of PARP1, PARP2 and PARP3 being developed in multiple tumor types, including ovarian and metastatic castration-resistant prostate cancers, as monotherapy, and in combination with other anti-cancer agents. Exploratory studies in other tumor types are also underway.
Rubraca is an unlicensed medical product outside of the US and Europe.
Rubraca US FDA Approved Indications
Ovarian Cancer
Rubraca is indicated for the maintenance treatment of adult women with recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer who are in a complete or partial response to platinum-based chemotherapy.
Prostate Cancer
Rubraca is indicated for the treatment of adult patients with a deleterious BRCA mutation (germline and/or somatic)-associated metastatic castration-resistant prostate cancer (mCRPC) who have been treated with androgen receptor-directed therapy and a taxane-based chemotherapy. This indication is approved under accelerated approval based on objective response rate and duration of response. Continued approval for this indication may be contingent upon verification and description of clinical benefit in confirmatory trials.
Select Important Safety Information
Myelodysplastic Syndrome (MDS)/Acute Myeloid Leukemia (AML) have occurred in patients treated with Rubraca and are potentially fatal adverse reactions. In 1146 treated patients, MDS/AML occurred in 20 patients (1.7%), including those in long term follow-up. Of these, 8 occurred during treatment or during the 28-day safety follow-up (0.7%). The duration of Rubraca treatment prior to the diagnosis of MDS/AML ranged from 1 month to approximately 53 months. The cases were typical of secondary MDS/cancer therapy-related AML; in all cases, patients had received previous platinum-containing regimens and/or other DNA damaging agents. In TRITON2, MDS/AML was not observed in patients with mCRPC (n=209) regardless of homologous recombination deficiency (HRD) mutation.
Do not start Rubraca until patients have recovered from hematological toxicity caused by previous chemotherapy (≤ Grade 1). Monitor complete blood counts for cytopenia at baseline and monthly thereafter for clinically significant changes during treatment. For prolonged hematological toxicities (> 4 weeks), interrupt Rubraca or reduce dose and monitor blood counts weekly until recovery. If the levels have not recovered to Grade 1 or less after 4 weeks or if MDS/AML is suspected, refer the patient to a hematologist for further investigations, including bone marrow analysis and blood sample for cytogenetics. If MDS/AML is confirmed, discontinue Rubraca.
Based on its mechanism of action and findings from animal studies, Rubraca can cause fetal harm when administered to a pregnant woman. Apprise pregnant women of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment and for 6 months following the last dose of Rubraca. For males on Rubraca treatment who have female partners of reproductive potential or who are pregnant, effective contraception should be used during treatment and for 3 months following the last dose of Rubraca.
Most common adverse reactions in ARIEL3 (≥ 20%; Grade 1-4) were nausea (76%), fatigue/asthenia (73%), abdominal pain/distention (46%), rash (43%), dysgeusia (40%), anemia (39%), AST/ALT elevation (38%), constipation (37%), vomiting (37%), diarrhea (32%), thrombocytopenia (29%), nasopharyngitis/upper respiratory tract infection (29%), stomatitis (28%), decreased appetite (23%), and neutropenia (20%).
Most common adverse reactions in TRITON2 (≥ 20%; Grade 1-4) were fatigue/asthenia (62%), nausea (52%), anemia (43%), AST/ALT elevation (33%), decreased appetite (28%), rash (27%), constipation (27%), thrombocytopenia (25%), vomiting (22%), and diarrhea (20%).
Co-administration of rucaparib can increase the systemic exposure of CYP1A2, CYP3A, CYP2C9, or CYP2C19 substrates, which may increase the risk of toxicities of these drugs. Adjust dosage of CYP1A2, CYP3A, CYP2C9, or CYP2C19 substrates, if clinically indicated. If co-administration with warfarin (a CYP2C9 substrate) cannot be avoided, consider increasing frequency of international normalized ratio (INR) monitoring.
Because of the potential for serious adverse reactions in breast-fed children from Rubraca, advise lactating women not to breastfeed during treatment with Rubraca and for 2 weeks after the last dose.