At the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting, researchers presented detailed clinical trial results highlighting the success of the new cancer drug RSO-021 in treating mesothelioma.

RSO-021 was effective and well tolerated in phase 1 of the trial, suggesting it could eventually become another treatment option for mesothelioma patients.

Developed by clinical biotech company RS Oncology, this medication essentially “pumps the brakes” on the cancer cell growth process, eventually leading to tumor death.

Earlier, in February 2024, a team of researchers investigating RSO-021 announced they had successfully dosed the first patient in phase 2 of a clinical trial that included patients diagnosed with pleural mesothelioma.

“RSO-021 is an exciting novel anti-cancer treatment that can potentially help a global population of cancer patients who are left with little to no options. Commencing the phase 2 portion of our trial presents a major milestone for patients and their caregivers.”

- Jarrett Duncan, CEO of RS Oncology

RSO-021 is just one example of new targeted therapies for mesothelioma that offer hope to patients with limited treatment options.

Mesothelioma Hope talked with Dr. Brian Cunniff, Chief Science Officer at RS Oncology, about the trial’s initial findings and what could be next for mesothelioma treatment.

How RSO-021 Treats Mesothelioma

Dr. Cunniff told Mesothelioma Hope that mesothelioma cells require increased energy to grow. The experimental drug RSO-021 aims to slow that energy exponentially.

“A normal cell is like a car driving at 65 mph, but a cancer cell is a car driving at 120 mph. The operation of the car at that speed requires the engine to be operating perfectly,” explained Dr. Cunniff. “This new drug is like sticking a potato in the tailpipe of the cancer cell. RSO-021 binds to the PRX3 enzyme that keeps the cell functioning properly and disables it.”

Dr. Sean Dulloo, one of the trial’s researchers, highlighted three trial participants.

Each patient was diagnosed with pleural mesothelioma and responded favorably to the new treatment.

All three patients experienced reduced fluid build-up in the lining of the lungs (pleural effusion) as well as a reduction in the size of their tumors. The drug completely stopped fluid from draining into the lung lining for two patients and significantly decreased it in the third.

“Essentially we have a drug that is reducing pleural effusion as well as treating the cancer,” said Dulloo in his presentation.

The new mesothelioma treatment RSO-021 works differently than immunotherapy and chemotherapy drugs because it directly targets the enzymes in cancerous cells without the risk of damaging healthy cells in the process.

“This therapy was specifically researched and developed for mesothelioma to give patients another option for treatment. No other mesothelioma drug works like this,” said Dr. Cunniff.

Get our Free Mesothelioma Guide shipped overnight to learn more about treatments for this cancer.

Investing in New Mesothelioma Treatment

Mesothelioma is a rare and aggressive form of cancer caused by exposure to asbestos. Tiny thread-like asbestos fibers can be inhaled and remain in the lungs for decades before causing cancerous tumors to form.

Did You Know?

Those most at risk of developing mesothelioma include military veterans and trade workers due to the widespread use of asbestos in shipbuilding, construction, and other industries from the 1930s to the early 1980s.

“Even though mesothelioma is rare, there are some incredible scientists and doctors who are passionate about studying this disease. They are very invested in finding new therapies,” said Dr. Cunniff. “It can be frustrating for patients who run out of options. We’re working to bring as many options as possible to improve patient outcomes and quality of life.”

Since the first phase of the RSO-021 study ended in September 2023, Dr. Cunniff and the rest of his UK-based research team have worked tirelessly to prepare for the next phases of the clinical trial, which will eventually begin enrolling patients in the United States.

Phase 1 Trial Results From the ASCO 2024 Annual Meeting

On June 3, 2024, researchers presented data from phase 1 of the RSO-021 clinical study known as MITOPE. MITOPE is a first-in-human clinical study to find out more about how RSO-021 works and if it could help pleural mesothelioma patients.

The primary goal of phase 1 was to determine the safety and tolerability level of RSO-021. Researchers set a secondary goal of establishing key anti-tumor activity like stability in cell growth and decrease in tumor size.

The study team found that:

  • 70% of patients had a partial response, meaning their tumors shrank
  • Tumors shrunk by 59% at a dose of 90 milligrams per week

“RSO-021 represents a new class of drugs with a first-in-class anticancer mechanism. The safety and efficacy observed in the phase 1 trial is supported by strong pre-clinical rationale,” stated Dr. Cunniff.

Researchers hope RSO-021 could join other new treatments that have been approved for mesothelioma in recent years. In the meantime, phase 2 of the trial is currently testing RSO-021 as a standalone mesothelioma treatment and in combination with other therapies.

Mesothelioma Hope’s nurses and Patient Advocates can help you access the latest mesothelioma treatments and enroll in clinical trials. Call us today at (866) 608-8933 to get started.

Get Help Finding Mesothelioma Treatment Near You

Mesothelioma is a devastating cancer that affects thousands of families every year. Mesothelioma Hope is dedicated to helping those impacted by this disease find the treatment and support they need.

If you or a loved one has been diagnosed with mesothelioma, our Patient Advocates can connect you with top specialists, cancer centers, and clinical trials for new treatments that may help you live longer.

Use our Free Mesothelioma Doctor Match for help finding the best treatment.

Mesothelioma Guide Images
Get Your Free 2024 Mesothelioma Guide
  • Symptoms & staging
  • Average prognosis
  • Life-extending treatments

Get Your Free Guide

beth swantekWritten by:

Contributing Author at Mesothelioma Hope

Beth Swantek has been writing about the dangers of asbestos since 2013. Beth served as a media professional for over 30 years and began her career as a broadcast journalist. After her daughter suffered a traumatic brain injury at birth, Beth has devoted her life to helping men and women experiencing deep loss — such as those living with mesothelioma.

Our Promise to You
Our Promise to You
  1. Business Wire. (2023). RS Oncology Announces Completion of First-in-Human Phase 1 Clinical Trial of RSO-021, a Novel Irreversible Inhibitor of Mitochondrial PRX3. Retrieved June 13, 2024, from
  2. Business Wire. (2024). RS Oncology Announces First Patient Dosed in Phase 2 Clinical Study (MITOPE) Investigating RSO-021 for the Treatment of Malignant Pleural Mesothelioma and Metastatic Disease to the Lung. Retrieved June 13, 2024, from 
  3. Fennell, Dean Anthony, et al. (2024, May 29). First-in-human phase I clinical trial of RSO-021, a first-in class covalent inhibitor of mitochondrial peroxiredoxin 3 (PRX3), in patients with malignant pleural effusion due to mesothelioma and other advanced solid tumors (MITOPE). JCO 42, 3019-3019(2024). Retrieved June 13, 2024 from
  4. Morningstar. (2024, June 3). RS Oncology Announces Positive Data from a Phase 1 Clinical Trial of RSO-021, a First-in-Class Therapeutic for Malignant Pleural Mesothelioma. Retrieved June 13, 2024, from
  5. R/S Oncology Symposium. International Mesothelioma Interest Group Conference. (Lille, France, 2023). Retrieved June 13, 2024, from[…]ical-development-for-Mesothelioma-and-lung-cancer-patients

Get Your Free 2024 Mesothelioma Guide

  • Symptoms & staging
  • Average prognosis
  • Life-extending treatments
Get Your Free Guide Now
Mesothelioma guide