Experimental Oral Drug GRWD5769 Shrinks Tumors by 30% in Six Major Cancer Types During Early-Phase Trial

Published: June 4, 2026

CHICAGO — A groundbreaking experimental cancer drug called GRWD5769 has demonstrated the ability to shrink tumors by at least 30% across six of the world’s most common and hard-to-treat cancer types. The highly anticipated clinical results were presented this week at the world’s largest cancer conference, the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago.

The new oral “smart drug,” developed by Oxford-based biotechnology company Greywolf Therapeutics, works via a unique mechanism: it strips cancer cells of their ability to hide from the body’s immune system. This biological evasion tactic—often compared to an “invisibility cloak”—has historically hindered the effectiveness of existing immunotherapies, leaving millions of advanced cancer patients worldwide with few therapeutic alternatives.

Key Trial Findings: Breaking Down the Data

The clinical breakthrough emerged from the EMITT-1 global clinical trial, an early-stage study conducted across 28 leading cancer centers in the United Kingdom, France, Spain, and Australia. The trial evaluated 83 evaluable patients diagnosed with advanced forms of non-small cell lung, bowel (microsatellite stable colorectal), head and neck, bladder (urothelial), liver, and cervical cancers.

Crucially, all participants entered the trial with heavily pre-treated, metastatic malignancies that had already developed secondary resistance to standard therapies and had previously failed conventional immunotherapy blockades.

The experimental regimen combined the twice-daily oral pill GRWD5769 with cemiplimab, an established intravenous immunotherapy drug. The trial yielded significant tumor shrinkage and prolonged disease stability across all six distinct cohorts:

• Tumor Shrinkage: Measurable tumor reduction occurred in 26 out of the 83 patients, with 15 individuals achieving an objective tumor shrinkage of at least 30%.

• Response Rates: The combination treatment achieved objective response rates (ORR) ranging between 13% and 36% across the variable cancer types, with deep tumor reductions reaching up to 95% in select cases.

• Disease Control: The therapy successfully halted the progression of aggressive disease for a minimum of six months, resulting in high Durable Clinical Benefit (DCB) rates.

Stripping the “Invisibility Cloak”: How the Drug Works

Traditional immunotherapy has revolutionized modern oncology by essentially “taking the brakes off” the body’s T-cells (immune cells), allowing them to hunt down and eliminate abnormal growths. However, this method fails in roughly two-thirds of patients.

Cancers frequently manipulate a specific cellular enzyme called endoplasmic reticulum aminopeptidase 1 (ERAP1). This enzyme acts like a faulty editor, trimming and altering the peptide “wanted posters” displayed on the surface of tumor cells. Because these surface proteins are altered, passing T-cells fail to recognize the threat, allowing the cancer to multiply unchecked.

GRWD5769 is a first-in-class, highly selective ERAP1 inhibitor. By blocking this enzyme on a cyclical three-week “on/off” schedule, the drug continuously shifts and unmasks the true protein markers of the tumor.

“GRWD5769 addresses this issue by inhibiting ERAP1, effectively unveiling cancer cells to T-cells that were previously unable to locate them,” noted the Greywolf Therapeutics research team.

When paired with cemiplimab, it delivers a potent one-two punch: GRWD5769 removes the cancer’s physical disguise, while the immunotherapy empowers the newly unblinded T-cells to mount a targeted attack.

Expert Commentary and Clinical Optimism

Medical experts at ASCO expressed strong encouragement regarding the drug’s safety-to-efficacy profile, a rare pairing in early oncology trials.

“For a drug that is given as a tablet, this is very impressive,” stated Professor Fiona Thistlethwaite, the trial’s principal investigator and a consultant medical oncologist at The Christie NHS Foundation Trust in Manchester, England. “It’s early days, and we need further studies, but this is a new drug with a new mechanism that clearly helps immunotherapy perform more effectively.”

Thistlethwaite added that experiencing strong efficacy signals across six highly resistant tumor types alongside remarkably few side effects is highly unusual during Phase 1 trials, where investigators are primarily looking for toxicities. “There’s a lot more work to be done before it reaches the clinic, but… it gives me genuine optimism.”

Independent specialists not involved in the trial shared this positive outlook while emphasizing the need for structured validation.

“The biological mechanism driving this trial is elegant, and the early responses—particularly in microsatellite stable (MSS) bowel cancer without liver metastases where immunotherapies are currently unlicensed and ineffective—are a clinically meaningful signal,” commented an independent oncologist attending the ASCO sessions. “However, the ultimate test will lie in transitioning this data into randomized, controlled trials.”

Patient Convenience and a Favorable Safety Profile

Beyond its clinical efficacy, GRWD5769 offers a distinct quality-of-life advantage over traditional chemotherapies. Administered as a simple capsule taken by mouth at home, it reduces the need for frequent, grueling hospital stays associated with heavy intravenous regimens.

Furthermore, the combination treatment demonstrated a favorable tolerability profile with no new safety signals. The vast majority of reported adverse events were classified as Grade 1 (mild). Immune-related adverse reactions occurred in only 12 patients, with just a single Grade 3 event (immune-mediated hepatitis) requiring drug discontinuation.

This low toxicity profile means patients can comfortably remain on the regimen for extended periods, paving the way for the pill to be safely combined with other standard frontline cancer therapies.

Crucial Public Health Context and Study Limitations

While the data marks a significant milestone in precision oncology, health professionals emphasize that the drug is not an immediate cure-all and carries standard early-phase limitations:

• Early Phase Limitations: This was primarily a Phase 1b expansion study designed to determine safe dosing and early signals. Historically, Phase 1 cancer trials average a 12% to 18% overall response rate. GRWD5769’s 13% to 36% range is highly favorable, but larger Phase 2 and Phase 3 trials are required to firmly prove long-term survival benefits.

• Small Patient Cohorts: Though 83 patients total is a solid baseline, individual cancer sub-type groups remain small (e.g., 14 patients in the bladder cohort).

• Absence of a Control Arm: The current trial phase lacks a cemiplimab-only comparison group. This makes it difficult to definitively isolate how much of the positive tumor shrinkage is purely driven by GRWD5769 versus a patient’s response to an immunotherapy re-challenge.

Moving Forward: What This Means for Patients

For health-conscious consumers and oncology patients, GRWD5769 represents a paradigm shift away from broadly toxic drugs toward molecularly precise, supportive therapies that work in harmony with the body’s natural defenses.

Currently, the drug remains strictly experimental and is not available for prescription in general clinical settings. The EMITT-1 trial continues to expand, with plans underway to advance the drug into randomized Phase 2 trials to evaluate long-term outcomes through early 2027. Advanced cancer patients interested in this specific line of antigen-modulation therapy are encouraged to consult their primary oncologists regarding clinical trial eligibility.

References

• https://www.ndtv.com/health/smart-cancer-drug-can-shrink-tumours-by-30-in-early-trial-11584989

Medical Disclaimer: This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.