MOUNTAINEER-03: Phase 3 study of tucatinib, trastuzumab, and mFOLFOX6 as first-line treatment in HER2+ metastatic colorectal cancer—Trial in progress

TPS261

Background: Current standard of care (SOC) for treatment (tx) of metastatic colorectal cancer (mCRC) is multi-agent chemotherapy, w/ or w/o a VEGF- or EGFR-inhibitor. HER2 is a validated clinical target in breast and gastric cancers. HER2 amplification occurs in 3%-5% of patients (pts) w/ mCRC; the rate of HER2 amplification can increase to ~10% in pts w/ RAS/BRAF wild-type mCRC tumors. Tucatinib (TUC), a highly selective, HER2-directed tyrosine kinase inhibitor, is approved in multiple regions for HER2+ metastatic breast cancer and is being investigated in gastrointestinal cancers. MOUNTAINEER (NCT03043313) evaluated the safety and efficacy of TUC and trastuzumab (Tras) in pts w/ tx refractory RAS wild-type, HER2+ mCRC. Results from the primary endpoint analysis showed clinically meaningful activity (confirmed ORR of 38.1% and median DOR of 12.4 months) and demonstrated TUC + Tras was well tolerated with a low discontinuation rate (5.8%) and no deaths due to AEs. MOUNTAINEER-03 will further investigate TUC in combo w/ mFOLFOX and Tras in pts w/ RAS wild-type, HER2+ mCRC. Methods: MOUNTAINEER-03 (NCT05253651) is a global, open label, randomized, phase 3 study for 1L tx of HER2+ and RAS wild-type mCRC. Approximately 400 pts will be randomized 1:1 to the TUC experimental arm (TUC [300 mg PO BID] + Tras + mFOLFOX) or the SOC arm (mFOLFOX alone or in combo w/ either bevacizumab or cetuximab). HER2 status is determined centrally w/ tissue based HER2 immunohistochemistry and in situ hybridization assays. Eligible pts must not have received prior tx in the metastatic setting but may have received adjuvant tx if completed > 6 months prior to enrollment. Pts must be ≥18 years of age w/ an ECOG performance status of ≤1 and RAS wild-type mCRC. Pts w/ treated stable central nervous system metastases are eligible. Randomization is stratified by primary tumor location (left-sided vs other) and liver metastases (presence/absence). Primary endpoint is progression-free survival per RECIST v1.1, assessed by blinded independent central review (BICR). Key secondary endpoints are overall survival and confirmed objective response rate per RECIST v1.1 assessed by BICR. Enrollment is ongoing in the US, w/ global sites planned. Clinical trial information: NCT05253651 .

Pembrolizumab plus chemotherapy for previously untreated, HER2-negative unresectable or metastatic advanced gastric or gastroesophageal junction (G/GEJ) adenocarcinoma: KEYNOTE-859

TPS263

Background: For patients with unresectable, locally advanced recurrent or metastatic G/GEJ cancer, the standard of care includes a fluoropyrimidine plus a platinum-based agent as first-line therapy. The PD-1 inhibitor pembrolizumab has demonstrated durable antitumor activity in this patient population across lines of therapy. Herein, we describe the randomized, double-blind, phase 3 KEYNOTE-859 trial (NCT03675737) of first-line pembrolizumab plus chemotherapy in patients with advanced G/GEJ adenocarcinoma. Methods: Patients with histologically or cytologically confirmed, locally advanced unresectable or metastatic G/GEJ adenocarcinoma with known PD-L1 expression status, HER2-negative disease, measurable disease per RECIST v1.1, and ECOG performance status of 0 or 1 will be randomly assigned 1:1 to receive pembrolizumab plus chemotherapy or placebo plus chemotherapy. Randomization will be stratified by geographic region (Europe/Israel/North America/Australia vs Asia vs rest of world), PD-L1 tumor expression status (combined positive score < 1 vs ≥1), and combination chemotherapy (FP vs CAPOX). Pembrolizumab or placebo will be administered at 200 mg IV every 3 weeks (Q3W). The chemotherapy regimen will be investigator’s choice of FP (continuous infusion of 5-fluorouracil [800 mg/m2/day on days 1-5 of each cycle] plus IV cisplatin [80 mg/m2] Q3W) or CAPOX (oral capecitabine [1000 mg/m2 twice daily on days 1-14 of each cycle] plus IV oxaliplatin [130 mg/m2 on day 1 of each cycle] Q3W). Duration of cisplatin or oxaliplatin may be capped at 6 cycles per local country guidelines; treatment with 5-fluorouracil or capecitabine may continue per protocol. Treatment with pembrolizumab or placebo will continue for ≤35 administrations (~2 years) or until disease progression, unacceptable toxicity, intercurrent illness that prevents further administration of treatment, investigator decision, or noncompliance. Imaging will be performed at screening and subsequently every 6 weeks until disease progression, start of new anticancer treatment, withdrawal of consent, or death. Adverse events will be monitored throughout the study from the time of randomization to 30 days after the last dose of study treatment (90 days for serious adverse events). The dual primary end points are OS and PFS per RECIST v1.1 as assessed by blinded independent central review (BICR). Secondary end points include ORR and DOR per RECIST v1.1 as assessed by BICR, safety, and tolerability. Enrollment is ongoing. Clinical trial information: NCT03675737.

A phase I study of TRC105 anti-endoglin (CD105) antibody in metastatic castration-resistant prostate cancer

OBJECTIVE

TRC105 is a chimeric immunoglobulin G1 monoclonal antibody that binds endoglin (CD105). This phase I open-label study evaluated the safety, pharmacokinetics and pharmacodynamics of TRC105 in patients with metastatic castration-resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

Patients with mCRPC received escalating doses of i.v. TRC105 until unacceptable toxicity or disease progression, up to a predetermined dose level, using a standard 3 + 3 phase I design.

RESULTS

A total of 20 patients were treated. The top dose level studied, 20 mg/kg every 2 weeks, was the maximum tolerated dose. Common adverse effects included infusion-related reaction (90%), low grade headache (67%), anaemia (48%), epistaxis (43%) and fever (43%). Ten patients had stable disease on study and eight patients had declines in prostate specific antigen (PSA). Significant plasma CD105 reduction was observed at the higher dose levels. In an exploratory analysis, vascular endothelial growth factor (VEGF) was increased after treatment with TRC105 and VEGF levels were associated with CD105 reduction.

CONCLUSION

TRC105 was tolerated at 20 mg/kg every other week with a safety profile distinct from that of VEGF inhibitors. A significant induction of plasma VEGF was associated with CD105 reduction, suggesting anti-angiogenic activity of TRC105. An exploratory analysis showed a tentative correlation between the reduction of CD105 and a decrease in PSA velocity, suggestive of potential activity of TRC105 in the patients with mCRPC. The data from this exploratory analysis suggest that rising VEGF level is a possible compensatory mechanism for TRC105-induced anti-angiogenic activity.

Dual antiangiogenic therapy using lenalidomide and bevacizumab with docetaxel and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC)

4569

Background: Previously, we had shown the potent anti−tumor activity of dual anti-angiogenic therapy by combining bevacizumab (B) and thalidomide (T) with docetaxel (D) and prednisone (P) in mCRPC (Ning JCO 2010). We hypothesized that combining lenalidomide (L), an analogue of T, with B, D, and P would have a more favorable efficacy/toxicity profile. Methods: All patients (pts) had chemotherapy−naïve mCRPC. Among the first 52 pts, 3 received L 15 mg daily, 3 had 20 mg daily, and the rest had 25 mg daily for 14 days of every 21−day cycle (C). The protocol was recently amended to enroll 11 more pts at L 15 mg; 2 pts have now been enrolled in this expansion cohort. All pts received D 75 mg/m2 and B 15 mg/kg on day 1 with P 10 mg and enoxaparin daily throughout each C. Pegfilgrastim was given on day 2. PSA each C with imaging after C2 and after every 3C. Dental exams with mandible CT scan at baseline, after C5, and every 6C. Results: 54 of 62 pts have been enrolled. Median age 65.5 (51−82), Gleason score 8 (5−10), on−study PSA 85.2 ng/ml (0.15−3520), and pre−study PSA doubling time 1.49 months (0.52−6.73). Median number of Cs was 16 (3−38). PFS was 22 months and probability of survival at 12 months was 90%. Forty-six (85.2%) and 42 (77.8%) pts had PSA declines of ≥50% and ≥75%, respectively. Of 30 pts with measurable disease there were 1 CR and 25 PR (86.7% overall RR). 17/54 pts were off study for radiographic disease progression and 8/54 for other reasons. Grade ≥2 toxicities included neutropenia (34/54), anemia (23/54), thrombocytopenia (7/54), hypertension (12/54), perianal fistula (3/54), rectal fissure (1/54), myocardial infarction (1/54), and osteonecrosis of the jaw (ONJ) (12/54, 22.0%). At the time of diagnosis of ONJ, 7/12pts were on bisphosphonates (BP), 2/12 had used BP previously, and 3/12 never used BP. The incidence of ONJ was comparable to 18.3% reported by Ning et al. A recent study of carboplatin plus weekly docetaxel reported an incidence of 29.3%. Conclusions: Dual anti-angiogenic therapy with, B and L, plus D and P was associated with high PSA (85.2%) and tumor (86.7%) responses in mCRPC, with manageable toxicities. The incidence of ONJ is comparable to other studies.

A phase I study of TRC105 (anti-CD105 [endoglin] antibody) in metastatic castration-resistant prostate cancer (mCRPC)

117

Background: Preclinical and clinical evidence demonstrates an important role for angiogenesis in mCRPC biology. CD105 (endoglin) is a transmembrane protein expressed on the surface of proliferating vascular endothelial cells. The expression of CD105 is required for the formation of new blood vessels. TRC105 is a human/murine chimeric IgG1 kappa monoclonal antibody that binds to human CD105 (endoglin). It inhibits angiogenesis and tumor growth through inhibition of endothelial cell proliferation, antibody-dependent cellular cytotoxicity, and induction of apoptosis. The primary objective is to evaluate safety and identify the maximum tolerable dose (MTD) of TRC105. Secondary objectives include the assessment of TRC105 pharmacokinetics, PSA response rate, evaluation of progression free survival (PFS), overall response rate (ORR) and overall survival (OS).

Methods: Patients with an ECOG performance status (PS) ≤ 2, progressive mCRPC and either chemotherapy-naïve or post-docetaxel treatment were eligible. Five cohorts of patients, on escalating dose levels, receive TRC105 intravenously at doses of 1, 3, 10 or 15 mg/kg IV every 2 weeks (cohorts 1, 2, 3, and 5) or 10 mg/kg IV weekly (cohort 4) on a 4 week cycle. Response is assessed with imaging studies every 2 months for the first four months and then every 3 months thereafter.

Results: Seventeen patients are enrolled in cohorts 1-5. Median age is 65 (range 48-87), median ECOG PS is 1 (range 0−2), median Gleason score is 8 (range 6−10), median on−study PSA is 147.5 (range 0.1-3373), and median number of prior (non-hormonal) therapies is 3 (range 0−6). Median time on study is 16 weeks (range 8-28 weeks). One patient experienced a dose limiting toxicity (grade 4 vasovagal episode) in cohort 5. PSA declines were seen in 6 patients ranging from 20% to 57% from baseline. Ten out of 12 patients with measurable soft tissue disease achieved stable disease for at least two cycles. Two patients remain on study (in cohort 5).

Conclusions: TRC105 is tolerated up to 15 mg/kg every two weeks with early evidence of clinical activity in mCRPC. Accrual is ongoing to evaluate ORR, PFS, and OS in the phase II portion of this study.

A SNP in CYP2C8 is not associated with the development of bisphosphonate-related osteonecrosis of the jaw in men with castrate-resistant prostate cancer

A single nucleotide polymorphism (SNP) in CYP2C8 (rs1934951), was previously identified in a genome-wide association study as a risk factor for the development of osteonecrosis of the jaw (ONJ) in patients receiving bisphosphonates (BPs) for multiple myeloma. To determine if the same SNP is also associated with the development of ONJ in men receiving BPs for bone metastases from prostate cancer, we genotyped 100 men with castrate-resistant prostate cancer treated with bisphosphonates for bone metastases, 17 of whom developed ONJ. Important clinical characteristics, including type and duration of bisphosphonate therapy, were consistent among those who developed ONJ and those who did not. We found no significant correlation between the variant allele and the development of ONJ (OR = 0.63, 95% CI: 0.165-2.42, P > 0.47). This intronic SNP in CYP2C8 (rs1934951) does not seem to be a risk factor for the development of bisphosphonate-related ONJ in men with prostate cancer. It is important to note that this is only the second study to investigate the genetics associated with BP-related ONJ and the first to do so in men with prostate cancer. More studies are needed to identify genetic risk factors that may predict the development of this important clinical condition.