CytomX’s Varsetatug Masetecan (EpCAM PROBODY® ADC) Continues to Demonstrate Positive Data Supporting Potential as a New Treatment Option in Late-Line Colorectal Cancer

Rhea-AI Summary

CytomX (Nasdaq: CTMX) reported positive Phase 1 expansion data for EpCAM PROBODY ADC varsetatug masetecan in late-line metastatic colorectal cancer. Confirmed ORRs were 32% at 10 mg/kg and 20% at 8.6 mg/kg; estimated median PFS was 7.1 and 6.8 months, respectively. Grade 3 diarrhea was 10% with updated prophylaxis. The company plans FDA interactions in mid-2026 and additional combination and expansion studies through 2026.

Positive

• Confirmed ORR of 32% at 10 mg/kg Q3W
• Estimated median PFS of 7.1 months at 10 mg/kg
• Disease control rate 88% across 7.2–10 mg/kg expansion doses
• FDA interaction targeted for mid-2026 toward registrational alignment

Negative

• Grade 3 diarrhea rate 10% despite prophylaxis in optimized cohort
• Significant Grade ≥3 hypokalemia: 13 events among 80 expansion patients
• One prior treatment-related Grade 5 acute kidney injury reported

News Market Reaction – CTMX

+68.80% 28.1x vol

31 alerts

+68.80% News Effect

+67.7% Peak in 4 hr 41 min

+$566M Valuation Impact

$1.39B Market Cap

28.1x Rel. Volume

On the day this news was published, CTMX gained 68.80%, reflecting a significant positive market reaction. Argus tracked a peak move of +67.7% during that session. Our momentum scanner triggered 31 alerts that day, indicating elevated trading interest and price volatility. This price movement added approximately $566M to the company's valuation, bringing the market cap to $1.39B at that time. Trading volume was exceptionally heavy at 28.1x the daily average, suggesting very strong buying interest.

Data tracked by StockTitan Argus on the day of publication.

Key Figures

Confirmed ORR at 10 mg/kg: 32% (6/19 patients) Confirmed ORR at 8.6 mg/kg: 20% (4/20 patients) Median PFS at 10 mg/kg: 7.1 months (95% CI: 3.9, NE) +5 more

8 metrics

Confirmed ORR at 10 mg/kg 32% (6/19 patients) Phase 1 expansion, late-line metastatic CRC, Q3W dosing

Confirmed ORR at 8.6 mg/kg 20% (4/20 patients) Phase 1 expansion, late-line metastatic CRC, Q3W dosing

Median PFS at 10 mg/kg 7.1 months (95% CI: 3.9, NE) Phase 1 expansion dose, late-line metastatic CRC

Disease Control Rate 88% (49/56 patients) Across 7.2–10 mg/kg expansion doses in Phase 1

Patients enrolled 93 patients Total enrollment in CTMX-2051-101 as of Jan 16, 2026

Grade 3 diarrhea rate 10% 20 patients in dose optimization (8.6 and 10 mg/kg) with updated prophylaxis

ORR at 11–12 mg/kg 30% (3/10 patients) Higher, non-expanded doses in Phase 1 study

Grade 5 TRAE 1 acute kidney injury case Previously reported at 7.2 mg/kg dose level

Market Reality Check

Price: $6.75 Vol: Volume 2,801,366 shares i...

normal vol

$6.75 Last Close

Volume Volume 2,801,366 shares is roughly in line with 20-day average of 2,780,577. normal

Technical Price $4.68 is trading above 200-day MA at $3.48, indicating a prior upward trend before this data.

Peers on Argus

Biotech peers show mixed action: several tracked names (e.g., ADCT, LRMR, TECX) ...

1 Up

Biotech peers show mixed action: several tracked names (e.g., ADCT, LRMR, TECX) had negative moves earlier, while AUTL appeared in momentum scanners with a 4.17% move up. With only one peer in momentum and mixed peer moves, trading around CTMX appears more stock-specific than sector-driven.

Historical Context

5 past events · Latest: Mar 04 (Neutral)

Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Mar 04	Earnings date notice	Neutral	+5.4%	Announced timing for Q4 and full-year 2025 financial results and call.
Feb 04	Conference presentations	Neutral	-6.6%	Management scheduled to present at two February 2026 investor conferences.
Jan 08	Business update	Positive	-0.9%	Outlined 2026 milestones for PROBODY pipeline, including Varseta-M trial plans.
Nov 25	Investor conferences	Neutral	+4.5%	Announced December 2025 Evercore and Piper Sandler conference appearances.
Nov 13	Jefferies conference	Neutral	-8.8%	CEO scheduled for fireside chat at Jefferies Global Healthcare Conference.

Pattern Detected

Recent CTMX news often led to sizable but directionally inconsistent moves, with several neutral or positive updates followed by both gains and declines.

Recent Company History

Over the last six months, CytomX has mainly issued corporate and investor-relations updates. These include multiple conference presentations in Nov–Dec 2025, a 2026 business and clinical milestones update on Jan 8, 2026 that highlighted plans for Varsetatug Masetecan Phase 1 expansions, and an earnings date announcement on Mar 4, 2026. Price reactions ranged from a +5.41% move on the earnings date notice to a -8.75% drop on a conference announcement, indicating that investor responses to non-clinical headlines have been volatile and not consistently aligned with the apparent tone of the news.

Regulatory & Risk Context

Active S-3 Shelf

Shelf Active

Active S-3 Shelf Registration 2025-08-07

The company has an active Form S-3 shelf registration filed on 2025-08-07, currently shown as not yet effective and with 0 recorded usages in the provided context. Specific capacity details are not available in this dataset.

Market Pulse Summary

The stock surged +68.8% in the session following this news. A strong positive reaction aligns with t...

Analysis

The stock surged +68.8% in the session following this news. A strong positive reaction aligns with the clearly favorable efficacy and disease control signals reported for Varsetatug Masetecan in heavily pretreated colorectal cancer, including a confirmed ORR of 32% and median PFS of 7.1 months at 10 mg/kg. Past headlines for CTMX have produced volatile and sometimes divergent moves, so investors have previously reassessed enthusiasm after initial spikes. An active S-3 shelf and a short interest context outside this dataset could both be relevant when evaluating how sustainable any sharp upside move may be.

Key Terms

progression free survival, overall response rate, disease control rate, treatment-related adverse events, +4 more

8 terms

progression free survival medical

"Estimated progression free survival of 7.1 months at 10 mg/kg and 6.8 months..."

Progression free survival is the length of time during and after a treatment when a disease, such as cancer, does not get worse or spread. It is an important measure because longer periods of stability can indicate that a treatment is effectively controlling the condition. For investors, it provides insight into the potential durability and success of a therapy or medication.

overall response rate medical

"Confirmed Overall Response Rate (ORR) 2 | 6% (1/17) | 20% (4/20) | 32% (6/19)"

Overall response rate is the percentage of patients in a clinical study whose measurable disease shrinks or disappears after receiving a treatment. Investors watch it like a product’s “hit rate” because higher response rates can signal a drug’s effectiveness, boost chances of regulatory approval and market demand, and affect a company’s future revenue prospects, similar to how a higher batting average suggests a more reliable player.

disease control rate medical

"Disease Control Rate (DCR) | 88% (15/17) | 90% (18/20) | 84% (16/19)"

The disease control rate is the share of patients in a clinical trial whose cancer or condition either shrinks or stops getting worse for a specified period after treatment. Think of it like the percentage of people for whom a treatment hits pause or nudges back the problem rather than letting it progress; higher rates suggest the therapy can meaningfully limit disease, which matters to investors assessing a drug’s potential efficacy and commercial value.

treatment-related adverse events medical

"the most common treatment-related adverse events (TRAEs) were diarrhea..."

Treatment-related adverse events are harmful or unwanted health effects that doctors or regulators determine were caused by a drug, vaccine, device, or other medical therapy. Investors care because how often and how severe these side effects are can shape regulatory approval, labeling, sales potential and legal risk — similar to how product defects can stop or damage a company's ability to sell an item.

interstitial lung disease medical

"No interstitial lung disease, febrile neutropenia or pancreatitis were observed."

A group of lung conditions that cause inflammation and scarring of the thin tissue between the air sacs, which makes it harder for oxygen to pass into the blood; imagine the lungs’ fine filters becoming stiff and less effective. Investors care because reports of interstitial lung disease can affect a drug’s safety profile, trigger regulatory warnings or label changes, and shift demand for treatments or create liability risks that influence a company’s valuation.

febrile neutropenia medical

"No interstitial lung disease, febrile neutropenia or pancreatitis were observed."

A serious medical condition in which a patient develops a fever while their level of infection-fighting white blood cells, called neutrophils, is very low. Think of the body’s defenses as an army: when its front-line soldiers are depleted, even a small invader can cause major problems, leading to hospital stays, treatment delays or extra supportive care. Investors watch febrile neutropenia because its frequency and severity affect demand for therapies, clinical trial outcomes, safety labeling and healthcare costs.

immunohistochemistry medical

"All patients with evaluable tumor biopsies had high EpCAM levels as measured by immunohistochemistry."

Immunohistochemistry is a laboratory method that uses labelled antibodies to highlight specific proteins inside thin slices of tissue, producing visible color where those proteins are present—like using colored highlighters to mark words on a page. Investors care because it provides concrete evidence about whether a drug hits its intended target, whether a diagnostic test works, and how a treatment affects tissues, all of which can affect clinical success, regulatory approval, and market value.

serious treatment related adverse events medical

"Serious treatment related adverse events (SAEs) in > 1 patient included diarrhea..."

Serious treatment related adverse events are significant harmful medical problems that clinicians judge to be caused by a drug or therapy, such as events that lead to hospitalization, permanent disability, life‑threatening conditions, or death. They matter to investors because they can stop or delay regulatory approval, shrink potential sales, force costly label changes or recalls, and raise legal and development expenses—like a safety defect that prevents a product from reaching the market.

AI-generated analysis. Not financial advice.

- Confirmed response rates in expansion cohorts of 32% at 10 mg/kg Q3W dose and 20% at 8.6 mg/kg Q3W -

- Estimated progression free survival of 7.1 months at 10 mg/kg and 6.8 months at 8.6 mg/kg -

- Grade 3 diarrhea rate of 10% in ongoing dose optimization cohorts -

- FDA interactions targeted for mid-year with goal to align on potential registrational trial design in late-line colorectal cancer (CRC) -

- Phase 1 study evaluating combination with bevacizumab initiated; Phase 1b/2 chemotherapy combination study to be initiated by the end of 2026 -

- Conference call on Monday, March 16 at 8:00 a.m. ET -

SOUTH SAN FRANCISCO, Calif., March 16, 2026 (GLOBE NEWSWIRE) -- CytomX Therapeutics, Inc. (Nasdaq: CTMX), a leader in the field of masked, conditionally activated biologics, today announced positive Phase 1 expansion data for its EpCAM PROBODY^® ADC, varsetatug masetecan (Varseta-M) in late-line metastatic CRC. The preliminary data are as of a January 16, 2026 data cutoff from the ongoing CTMX-2051-101 Phase 1 study.

“These latest Phase 1 data reinforce the potential of Varseta-M to meaningfully improve the standard of care in late-line colorectal cancer. We are now planning interactions with the FDA to discuss the initial registrational path for bringing this highly innovative, first-in-class ADC to the market in late-line CRC,” said Sean McCarthy, D. Phil, chief executive officer and chairman of CytomX.

McCarthy added, “Our ultimate vision is to reach a broad CRC patient population with Varseta-M, including in earlier lines of treatment, as well as to expand into additional EpCAM-expressing cancers. We aim to aggressively advance this novel therapy towards late-stage development for the benefit of patients as we set our sights on building CytomX into a commercial-stage company.”

“Patients with late-stage metastatic CRC face a poor prognosis and have very limited treatment options. These exciting clinical data demonstrate that Varseta-M can drive consistent and durable responses with a manageable tolerability profile in patients with heavily pretreated CRC, supporting its promise as a potential new treatment option for advanced CRC,” said Dr. Kimmie Ng, Associate Chief of the Division of Gastrointestinal Oncology at Dana-Farber Cancer Institute.

Varsetatug Masetecan Phase 1 Expansion Data Summary in Advanced, Late-line Colorectal Cancer

• The CTMX-2051-101 study was initiated in April 2024 with dose escalation proceeding through seven dose levels ranging from 2.4 mg/kg to 12 mg/kg. As of the data cutoff of January 16^th 2026, a total of 93 patients with late-line metastatic CRC had been enrolled in the study. 60 patients were enrolled across the Phase 1 expansion dose range of 7.2 mg/kg, 8.6 mg/kg, and 10 mg/kg of which 56 were efficacy evaluable as of the data cutoff.
• Starting in October 2025, the expansion doses of 8.6 mg/kg and 10 mg/kg were prioritized for dose optimization utilizing optimized adverse event management guidelines and adjusted ideal body weight (AIBW) dosing. 20 patients had been enrolled in expanded dose optimization as of the January 16^th data cutoff towards an enrollment goal of 40 patients.
  
  

Patient Characteristics:

• Patients enrolled in the study had previously received a median of 3 prior lines of therapy in the metastatic setting and 96% of patients had previously been treated with irinotecan. 76% of patients had liver metastases and 71% had KRAS mutations.
• Patients were not preselected based on EpCAM expression levels. All patients with evaluable tumor biopsies had high EpCAM levels as measured by immunohistochemistry.¹
  
  

Efficacy:

As of the data cutoff, 56 patients were efficacy-evaluable at the expansion doses of 7.2 mg/kg, 8.6 mg/kg, and 10 mg/kg Q3W. Median duration of follow-up across the efficacy-evaluable patient population was approximately 8 months. Efficacy data across the Phase 1 Expansion doses are summarized below in Table 1.

Table 1. Varseta-M Efficacy Summary by Phase 1 Expansion Dose

	7.2 mg/kg	8.6 mg/kg	10 mg/kg
Confirmed Overall Response Rate (ORR)2	6% (1/17)	20% (4/20)	32% (6/19)
Median Progression Free Survival (PFS)	5.5 mo. (95% CI: 2.5, NE)	6.8 mo. (95% CI: 2.8, NE)	7.1 mo. (95% CI: 3.9, NE)
Disease Control Rate (DCR)	88% (15/17)	90% (18/20)	84% (16/19)

• At the 8.6 mg/kg dose, the confirmed response rate was 20% with an estimated median PFS of 6.8 months and at the 10 mg/kg dose, the confirmed response rate was 32% with an estimated median PFS of 7.1 months.
• The disease control rate was 88% (49/56) across the expansion doses of 7.2 – 10 mg/kg.
• The doses of 8.6 mg/kg and 10 mg/kg have been prioritized for further evaluation with the goal of selecting a dose or doses for a registrational study.
• Dose optimization at 8.6 mg/kg and 10 mg/kg utilizing AIBW dosing and updated prophylaxis for adverse event management is ongoing.
• At the doses of 11 mg/kg Q3W and 12 mg/kg Q3W, which were not expanded for further evaluation, the overall response rate was 30% (3/10).
  
  

Safety:

As of the data cutoff, 93 patients were evaluable for safety including 80 patients across the expansion dose range of 7.2 mg/kg to 10 mg/kg. Varseta-M’s safety profile was generally consistent with data presented in Phase 1 dose escalation. Most treatment related adverse events were Grade 1 or Grade 2 in severity.   

• No interstitial lung disease, febrile neutropenia or pancreatitis were observed.
• The most common treatment-related adverse event (TRAE) was diarrhea which was generally manageable and reversible.
• In Phase 1 dose expansions starting in Q2 2025, prophylactic strategies for diarrhea management were investigated. In dose optimization starting in Q4 2025, an updated prophylaxis regimen of anti-motility medication (loperamide or diphenoxylate/atropine) plus budesonide was implemented.³
• In the 20 patients receiving the updated prophylactic regimen in dose optimization at doses of 8.6 mg/kg and 10 mg/kg, Grade 3 diarrhea was 10%.^4,5
• Overall, as of the January 16^th 2026 data cutoff, in the 80 patients treated at expansion and optimization doses ranging between 7.2 mg/kg to 10 mg/kg, the most common treatment-related adverse events (TRAEs) were diarrhea (68 pts, 19 Gr 3), nausea (44 pts, 4 Gr 3), vomiting (29 pts, 3 Gr 3), fatigue (32 pts, 2 Gr 3), hypokalemia (21 pts, 13 Gr 3+), and anemia (13 pts, 6 Gr 3). Serious treatment related adverse events (SAEs) in > 1 patient included diarrhea (4), vomiting (3), hypokalemia (3), dehydration (3), acute kidney injury (2), and colitis (2).
• As previously reported on August 13, 2025, there was one treatment-related grade 5 acute kidney injury (AKI) in a patient treated at the 7.2 mg/kg dose. The patient had a complex medical history including having a solitary kidney, and the AKI was determined to be secondary to Grade 3 nausea and Grade 2 diarrhea. No other Grade 5 TRAEs have been reported as of the January 16^th 2026 data cutoff.
• At the 11 mg/kg and 12 mg/kg doses, there were no dose limiting toxicities in dose escalation. The most common TRAEs across the patients in the 11 mg/kg dose (n=8) and 12 mg/kg dose (n=3) were diarrhea (9 pts, 6 GR 3), nausea, (8 pts, 0 Gr 3), and vomiting (8 pts, 1 Gr 3). Patients treated at the 11 and 12 mg/kg doses did not receive the optimized prophylactic regimen or adjusted ideal body weight dosing. 
  
  

Varsetatug Masetecan Next Steps:

• Additional efficacy and safety data from the Phase 1 study are expected to be presented at one or more medical meetings in 2026.
• The Company aims to align with the FDA in 2026 on a potential registrational study design for Varseta-M monotherapy in advanced CRC.
• A Phase 1 Varseta-M combination study with bevacizumab in CRC has been initiated and a Phase 1b/2 study in combination with bevacizumab and chemotherapy is expected to start by the end of 2026.
• Initiation of Phase 1 expansion cohort(s) in additional EpCAM-expressing indications is planned for 2H 2026.
  
  

CytomX Investor Event Information
Additional details will be provided on the Company’s Investor Call on March 16, 2026 at 8 a.m. ET. Participants may access the live webcast of the conference call from the Events and Presentations page of CytomX’s website at https://ir.cytomx.com/events-and-presentations. Participants may register for the conference call here and are advised to do so at least 10 minutes prior to joining the call. An archived replay of the webcast will be available on the company’s website for at least 30 days.

About CytomX Therapeutics, Inc.
CytomX is a clinical-stage, oncology-focused biopharmaceutical company focused on developing novel conditionally activated, masked PROBODY^® therapeutics designed to be localized to the tumor microenvironment. By pioneering a novel pipeline of localized biologics, powered by its PROBODY therapeutic platform, CytomX’s vision is to create safer, more effective therapies for the treatment of cancer. CytomX’s robust and differentiated pipeline comprises therapeutic candidates across multiple treatment modalities including antibody-drug conjugates (“ADCs”), cytokines and T-cell engagers. CytomX’s clinical-stage pipeline includes varsetatug masetecan (Varseta-M; CX-2051) and CX-801. Varseta-M is a masked, conditionally activated ADC armed with a topoisomerase-1 inhibitor payload and directed toward epithelial cell adhesion molecule (EpCAM). EpCAM is a highly expressed tumor antigen that has previously been undruggable due to expression on normal tissues. Varseta-M is designed to open a therapeutic window for this high potential target and is initially being developed for the treatment of metastatic colorectal cancer. Varseta-M was discovered in collaboration with ImmunoGen, now part of AbbVie. CX-801 is a masked interferon alpha-2b PROBODY^® cytokine with broad potential applicability in traditionally immuno-oncology sensitive as well as insensitive (cold) tumors. CX-801 is initially being developed for the treatment of metastatic melanoma. CytomX has established strategic collaborations with multiple leaders in oncology, including Amgen, Bristol Myers Squibb, Regeneron and Moderna. For more information about CytomX and how it is working to make conditionally activated treatments the new standard-of-care in the fight against cancer, visit www.cytomx.com and follow us on LinkedIn and X (formerly Twitter).

CytomX Therapeutics Forward-Looking Statements
This press release includes forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other important factors that are difficult to predict, may be beyond CytomX’s control, and may cause the actual results, performance, or achievements to be materially different from any future results, performance or achievements expressed or implied in such statements, including those related to the future potential of partnerships or collaboration agreements and projected cash runway. Accordingly, you should not rely on any of these forward-looking statements, including those relating to the potential benefits, safety and efficacy or progress of CytomX’s or any of its collaborative partners’ product candidates, including varsetatug masetecan (Varseta-M; CX-2051) and CX-801, the potential benefits or applications of CytomX’s PROBODY^® therapeutic platform, CytomX's planned interactions with the U.S. Food and Drug Administration and the ability to align on a potential registrational study design and regulatory pathway for varsetatug masetecan, CytomX’s or its collaborative partners’ ability to develop and advance product candidates into and successfully complete clinical trials, including the ongoing and planned clinical trials of varsetatug masetecan and CX-801 and the timing of initial and ongoing data availability for CytomX’s clinical trials, including varsetatug masetecan and CX-801, and other development milestones. Risks and uncertainties that contribute to the uncertain nature of the forward-looking statements include: the unproven nature of CytomX’s novel PROBODY^® therapeutic technology; uncertainties around the Company’s ability to raise sufficient funds to carry out its planned research and development; CytomX’s clinical trial product candidates are in the initial stages of clinical development and its other product candidates are currently in preclinical development, and the process by which preclinical and clinical development could potentially lead to an approved product is long and subject to significant risks and uncertainties, including the possibility that the results of preclinical research and early clinical trials, including initial varsetatug masetecan clinical trial results, may not be predictive of future results; the possibility that CytomX’s clinical trials will not be successful; the possibility that current preclinical research may not result in additional product candidates; CytomX’s dependence on the success of varsetatug masetecan and CX-801; CytomX’s reliance on third parties for the manufacture of the Company’s product candidates; possible regulatory developments in the United States and foreign countries, including China and the European Union; and the risk that we may incur higher costs than expected for research and development. Additional applicable risks and uncertainties include those relating to CytomX’s preclinical research and development, clinical development, and other risks identified under the heading "Risk Factors" included in CytomX’s Annual Report on Form 10-K filed with the SEC on March 16, 2026. The forward-looking statements contained in this press release are based on information currently available to CytomX and speak only as of the date on which they are made. CytomX does not undertake and specifically disclaims any obligation to update any forward-looking statements, whether as a result of any new information, future events, changed circumstances or otherwise.

PROBODY is a U.S. registered trademark of CytomX Therapeutics, Inc. All other trademarks are the properties of their respective owners.

Company Contact:
Chris Ogden
SVP, Chief Financial Officer
cogden@cytomx.com

Investor Contact:
Precision AQ
Stephanie Ascher
Stephanie.Ascher@precisionaq.com

Media Contact:
Precision AQ
Colleen Ketchum
Colleen.ketchum@precisionaq.com

^{_______________________
1} 96% of patients with an evaluable biopsy had an H score by immunohistochemistry above 250 and all patients had H scores above 200.
² Per RECIST v.1.1 criteria
³ Budesonide is a corticosteroid locally absorbed in the gastrointestinal (GI) tract.
⁴8.6 mg/kg and 10 mg/kg dosed utilizing adjusted ideal body weight (AIBW).   
⁵Based on March 2, 2026 data snapshot.

FAQ

What response rates did CTMX report for varsetatug masetecan in the March 16, 2026 update?

Confirmed ORRs were 32% at 10 mg/kg Q3W and 20% at 8.6 mg/kg Q3W. According to the company, these figures come from Phase 1 expansion data with a January 16, 2026 cutoff and approximately eight months median follow-up.

What progression-free survival did CytomX report for CTMX varsetatug masetecan in late-line CRC?

Estimated median PFS was 7.1 months at 10 mg/kg and 6.8 months at 8.6 mg/kg. According to the company, these PFS estimates are from the Phase 1 expansion cohort data with a January 16, 2026 data cutoff.

How severe were toxicities for CTMX’s Varseta-M in the March 16, 2026 data disclosure?

Most treatment-related adverse events were Grade 1–2; Grade 3 diarrhea was 10% with updated prophylaxis. According to the company, hypokalemia and some serious TRAEs occurred, and one prior treatment-related Grade 5 AKI was previously reported.

What regulatory and development next steps did CytomX (CTMX) announce on March 16, 2026?

The company plans FDA interactions targeted for mid-2026 to align on a potential registrational study for late-line CRC. According to the company, additional combination studies and expansion cohorts are expected through the end of 2026 and into 2H 2026.