Benzinga | Dec 20, 2021 04:07PM EST

CytomX Therapeutics Announces Preliminary Results For Ongoing Phase 2 Expansion Study Of CX-2029, A First-in-Class Antibody-Drug Conjugate Candidate Targeting The Transferrin Receptor, CD71

CytomX Therapeutics, Inc. (NASDAQ:CTMX), a leader in the field of conditionally activated therapeutics, today announced preliminary Phase 2 results in patients with either advanced squamous non-small cell lung cancer (sqNSCLC) or head and neck squamous cell carcinoma (HNSCC), who were treated with CX-2029 -- a CD71-directed conditionally activated antibody-drug conjugate (ADC) being co-developed by CytomX and AbbVie.

"We are pleased to report these first results from the ongoing Phase 2 expansion study of CX-2029, a novel ADC developed with the CytomX Probody Therapeutic platform. We are encouraged that the response rate in heavily-pretreated and unselected sqNSCLC patients at this recent data cut off is trending with our stated target of 20% and enrollment in this tumor type continues towards our goal of 25 efficacy-evaluable patients. No new safety signals were observed and we are also encouraged by the low discontinuation rate due to adverse events. These preliminary results corroborate our previous Phase 1 observations and open a potential sqNSCLC commercial opportunity in the growing post-checkpoint inhibitor setting where there are limited treatment options," said Sean McCarthy, D.Phil., president, chief executive officer and chairman of CytomX Therapeutics. "We continue to work closely with our partner, AbbVie, and look forward to completing the expansion phase of the CX-2029 development program and providing further data updates in 2022."

As of the data cutoff on October 29, 2021, 23 patients with sqNSCLC and 29 patients with HNSCC had received at least one dose of CX-2029 at 3 mg/kg (safety population), of whom 16 sqNSCLC patients and 25 HNSCC patients had at least one post baseline assessment (efficacy-evaluable population), including, per protocol, 5 patients (2 sqNSCLC and 3 HNSCC) enrolled in the previously reported Part B (tumor biopsy cohorts). The median follow-up time was 3.8 months (range, 0.2-20.1). In the 16 efficacy evaluable patients with sqNSCLC, objective response rate (ORR) by local investigator was 18.8 percent, including two confirmed partial responses (PRs) and one unconfirmed PR that confirmed seven days after the data cutoff. Two of these responses were ongoing and the third had a response duration of 5.6 months. The disease control rate (DCR), which includes patients with a complete response, PR or stable disease, was 87.5 percent. In the 25 efficacy evaluable patients with HNSCC, there was one confirmed PR (ORR 4.0%) and a DCR of 56.0 percent, including one unconfirmed PR. Below is a summary table.

sqNSCLC HNSCCSafety Efficacy Confirmed Safety Efficacy ConfirmedEvaluable Evaluable PR Evaluable Evaluable PRPart B 2 2 1 3 3 1Part C 21 14 2* 26 22 0*&# x2A;Total 23 16 3 29 25 1ORR 18.8% 4.0%

*Includes one unconfirmed PR that confirmed after the data cutoff. **One unconfirmed PR was observed (will not confirm).

Safety analysis was conducted on all sqNSCLC and HNSCC patients who received at least one dose of CX-2029 at 3 mg/kg (N=52), either in Part B (N=5), or in the expansion cohorts (N=47). The median number of prior therapies in the metastatic setting was two (range, 1-5) for sqNSCLC and three (range, 1-9) for HNSCC. All patients with sqNSCLC had received prior platinum and prior checkpoint inhibition; in HNSCC, all but one patient received prior platinum and all but two, prior checkpoint inhibition.

The safety profile was consistent with previous Phase 1 observations, with no new safety signals identified. The most common treatment-related adverse events (TRAEs) in 10% or more of patients (All Grade, Grade 3) were anemia (78.8%, 67.3%), infusion related reactions (69.2%, 3.8%), fatigue (19.2%, 1.9%), and nausea (13.5%, 0.0%), and decreased neutrophil count (13.6%, 9.6% (plus one Grade 4 event 1.9%)). The most common reason for treatment discontinuation was disease progression (44.2%), three patients (5.8%) discontinued for a treatment-related adverse event (anemia; 2 Grade 2, 1 Grade 3). TRAEs leading to dose interruption or reduction were 40.4% and 34.6%, respectively. Thirteen patients, eight with sqNSCLC and five with HNSCC, were still on treatment as of the data cut off.