Merck's New ADC Enters Phase 3, Offering Hope in Late-Stage Colon Cancer

DARMSTADT, Germany – May 21, 2026 – By Cynthia Ward

Merck, a leading science and technology company, has initiated a pivotal Phase 3 clinical trial for a highly anticipated cancer therapy, dosing the first patient in a study that could bring a new weapon to the fight against advanced colorectal cancer. The trial, named PROCEADE®-CRC-03, will evaluate precemtabart tocentecan (Precem-TcT), an investigational antibody-drug conjugate (ADC) designed to offer a lifeline to patients with metastatic colorectal cancer (mCRC) who have exhausted other treatment avenues.

This move marks a significant step forward for a potential first-in-class therapy targeting the CEACAM5 protein, which is prevalent in the vast majority of colorectal tumors. For a patient population facing a grim prognosis and dwindling options, the advancement of Precem-TcT into this late-stage study represents a tangible source of hope.

“Leveraging our novel payload-linker technology, Precem-TcT is the first CEACAM5-targeted ADC in clinical studies with an exatecan payload, rationally designed for stability and enhanced cancer cell killing activity,” said David Weinreich, MD, MBA, Global Head of R&D and Chief Medical Officer for Merck's Healthcare business. “The Phase 3 study and the enrollment of the first patient with Precem-TcT build on the Company’s more than 20 years of expertise in colorectal cancer, and highlight our commitment to advancing differentiated ADCs for heavily pretreated patients with limited treatment options.”

A Desperate Need for New Options

Colorectal cancer remains a global health crisis. It is the third most commonly diagnosed cancer and the second leading cause of cancer-related death worldwide. While early detection and treatment have improved, the outlook for patients whose cancer has spread, or metastasized, is far more challenging. For those with mCRC whose disease progresses after standard therapies, the path forward becomes increasingly difficult.

Currently, the standard of care for these heavily pretreated patients includes oral agents like regorafenib and trifluridine/tipiracil. While these drugs can offer modest survival benefits, they often come with significant side effects that impact quality of life. The five-year survival rate for stage 4 colorectal cancer remains below 20%, a stark statistic that underscores the urgent need for more effective and better-tolerated treatments.

“The PROCEADE®-CRC-03 Phase 3 study is designed to address significant unmet needs for patients with metastatic colon cancer whose disease has progressed after standard therapies,” commented Kanwal P.S. Raghav, MBSS, MD, from the Department of Gastrointestinal Medical Oncology at MD Anderson Cancer Center. He noted that the data from the earlier Phase 1 study suggested a manageable safety profile and encouraging early tumor response, providing a strong rationale for the large-scale pivotal trial.

The Science of a 'Smart Bomb'

Precem-TcT belongs to a class of drugs known as antibody-drug conjugates, often described as “smart bombs” or “guided missiles” for their precision. These therapies consist of three parts: a monoclonal antibody designed to seek out a specific protein on cancer cells, a highly potent chemotherapy payload, and a linker that connects the two.

The antibody in Precem-TcT targets CEACAM5, a protein found in high levels on the surface of approximately 90% of colorectal cancer cells but largely absent from healthy tissues. This specificity allows the drug to home in on the tumor while minimizing damage to the rest of the body. Once bound to a cancer cell, the ADC is internalized, and the linker releases its payload—a powerful topoisomerase 1 (TOP1) inhibitor called exatecan—directly inside the cell, triggering its destruction.

What makes Precem-TcT particularly promising is its sophisticated design. Preclinical research has shown it can induce a “bystander effect,” where the exatecan payload, once released, can permeate the cell membrane and kill neighboring cancer cells that may not even express the CEACAM5 target. This is a crucial advantage in treating heterogeneous tumors, where protein expression can vary from cell to cell, potentially leading to a more comprehensive and durable anti-tumor response.

A Strategic Push in a Competitive Arena

The advancement of Precem-TcT is a key part of Merck's broader strategy to establish itself as a leader in the fiercely competitive oncology market, particularly in the rapidly evolving ADC space. With its blockbuster immunotherapy Keytruda facing eventual patent expirations, the company is aggressively investing in a new generation of cancer drugs to secure its future pipeline. This includes a multi-billion dollar alliance with Kelun-Biotech that recently yielded a major Phase 3 win for another ADC, sacituzumab tirumotecan, in endometrial cancer.

Targeting CEACAM5 is not without its challenges. Sanofi previously experienced a high-profile setback when its own CEACAM5-targeted ADC, tusamitamab ravtansine, failed a Phase 3 trial for lung cancer. However, Merck is betting that its different payload and advanced linker technology can succeed where others have faltered. The company is not alone in its renewed interest; Pfizer and several smaller biotechs are also developing their own CEACAM5-directed therapies, making this a closely watched therapeutic area.

Merck's confidence is bolstered by encouraging results from the Phase 1 PROCEADE®-CRC-01 study. In a group of heavily pretreated patients, the drug demonstrated a confirmed objective response rate of 20.7% and a median progression-free survival of 6.9 months. While these numbers may seem modest, they are considered clinically meaningful in a patient population that has already failed multiple lines of therapy and for whom existing options offer limited benefit.

The global PROCEADE®-CRC-03 trial is a massive undertaking, aiming to enroll approximately 1,020 patients across 165 sites in 20 countries. The study will assess Precem-TcT both as a monotherapy and in combination with bevacizumab, a standard anti-angiogenic drug. Its large scale reflects Merck’s significant commitment and the potential blockbuster status of the drug if it proves successful. For thousands of patients and their families, the results of this trial cannot come soon enough.