Shares of CytomX Therapeutics (CTMX) rose slightly after hours on Sept. 9 as the biotech reported pipeline progress at the 12th Annual Cantor Fitzgerald Global Healthcare Conference.
CEO Sean McCarthy opened the session by highlighting the company's masked-intercept biologics platform and an expanded collaboration with Regeneron, which carried a $37 million upfront payment.
The centerpiece of the update was varsetatug masetecan (varseta-M), an EpCAM-targeting antibody-drug conjugate (ADC) that inhibits topoisomerase I, being developed for heavily pretreated colorectal cancer. In late-line fourth-line trials, varseta-M produced an overall response rate of 20% to 30%, compared with 1% to 2% for standard of care, McCarthy said.
Safety data from the Phase I optimization cohorts pointed to meaningful improvement in dose-limiting toxicity management. Grade 3 diarrhea fell to approximately 10% among the first 20 patients who received budesonide once daily for seven days of each three-week cycle, alongside loperamide and adjusted ideal body weight dosing. Of 14 patients treated with budesonide for diarrhea, 12 demonstrated at least a one-grade improvement. McCarthy said the company aims to keep grade-3 diarrhea rates within a 10% to 20% commercial-acceptability range.
No interstitial lung disease cases were observed, and hematologic toxicity remained low, he added. The EpCAM target, initially identified in colorectal cancer in 1979, has historically been hampered by non-specific toxicity; varseta-M's masking strategy is designed to address that limitation.
The Phase I study has enrolled 113 patients across escalation, expansion, and optimization cohorts. Expansion doses tested include 7.2 mg/kg, 8.6 mg/kg, and 10 mg/kg administered every three weeks, with progression-free survival of roughly six to seven months at the higher doses.
CytomX outlined several near-term milestones. Full data from the 113-patient Phase I trial—including response rates, progression-free survival, and overall survival based on the first 73 patients—are expected by year-end 2024, alongside FDA discussions to review the registrational strategy, including patient population, comparator arm, and dose selection. A 5-fluorouracil combination study is slated to begin in the fourth quarter, with initial bevacizumab-combination data possible in the first half of 2025. McCarthy noted the company's "number-one goal" is to bring the drug to patients as quickly as possible.
Also discussed was the CX-801 masked interferon alfa-2b program, with initial safety and efficacy data expected in melanoma (monotherapy and in combination with Merck's Keytruda) in early 2025.
In other collaboration news, CytomX highlighted partnerships with AbbVie on ABBV-400, a c-Met ADC, and Merck Serono on a CEACAM5-targeting ADC. The expanded Regeneron alliance adds to a growing ADC portfolio built on the company's proprietary masking technology.
On the market side, CytomX estimated the fourth-line colorectal cancer population at roughly 10,000 to 20,000 treatable patients in the U.S. By comparison, third-line bevacizumab plus LONSURF yields an overall survival of about nine to 11 months, while late-line fourth-line overall survival sits at six to seven months with a progression-free survival of approximately three months.
CTMX shares were last seen around $3.29, down 1.79% in regular trading, with after-hours price at $3.30. The stock has returned 74.6% over the past year with a beta of 2.14. Analyst price targets range from $6 to $16.
