By Billy Candra 
A pioneering, federally funded clinical trial has achieved a significant breakthrough in breast cancer management, demonstrating the feasibility of identifying survivors at heightened risk of relapse due to dormant cancer cells and effectively neutralizing these cells using existing, repurposed drugs. This landmark research, spearheaded by scientists from the Abramson Cancer Center at the University of Pennsylvania and Penn’s Perelman School of Medicine, was formally published today in the prestigious journal Nature Medicine, heralding a potential paradigm shift in post-treatment care for breast cancer patients.
The persistent specter of recurrence looms large for many breast cancer survivors, casting a long shadow even after successful primary treatments. While advancements in early detection and therapeutic strategies have dramatically improved overall survival rates, the grim reality is that once breast cancer relapses, particularly as metastatic disease, it remains largely incurable. This devastating outcome affects approximately 30 percent of individuals diagnosed with breast cancer, who are then often relegated to continuous, indefinite treatment regimens that can manage, but not eradicate, the disease. The timing of recurrence can vary widely, with aggressive subtypes like triple-negative and HER2-positive breast cancers often returning within a few years, while hormone-receptor-positive (ER+) cancers can lie dormant for decades before reactivating. Until now, clinicians lacked a reliable method to identify these high-risk individuals in real-time or to intervene with preventative treatments capable of intercepting an otherwise incurable relapse.
The Invisible Threat: Understanding Dormant Cancer Cells
The foundation of this groundbreaking study lies in extensive prior research into the nature of dormant tumor cells, often referred to as "sleeper cells" or Minimal Residual Disease (MRD). These insidious cells are residual cancer cells that survive initial therapies but do not actively divide or grow. Instead, they enter a quiescent state, lying in wait in various organs, including the bone marrow, for years or even decades. Crucially, because these cells are not actively proliferating, they often evade detection by standard imaging techniques such as mammograms, CT scans, or PET scans, which are designed to identify metabolically active tumors. This stealth characteristic makes them a formidable challenge in cancer management.
The danger arises when these sleeper cells reactivate. Once roused from their dormancy, they can begin to proliferate, expand, and eventually circulate in the bloodstream, leading to the development of metastatic breast cancer – the stage at which the disease has spread to distant parts of the body and becomes notoriously difficult to treat. Patients diagnosed with MRD are known to face a significantly higher likelihood of breast cancer recurrence and a diminished overall survival rate compared to those without detectable residual disease. The inability to monitor or target these cells has long been a critical unmet need in oncology.
A Novel Approach: Targeting Dormancy Pathways
The current research builds directly on the foundational work of Lewis Chodosh, MD, PhD, chair of Cancer Biology and senior author of the study. Dr. Chodosh’s earlier investigations meticulously mapped out the intricate biological pathways that enable dormant tumor cells to persist in patients for extended periods. His team discovered that the biology of these "sleeping" cells is profoundly different from that of actively growing cancer cells. This distinction is paramount, as it suggests that drugs ineffective against active tumors might, paradoxically, be highly potent against dormant ones.
"Our research shows that this sleeper phase represents a unique window of opportunity to intervene and eradicate these dormant tumor cells before they have the chance to re-emerge as aggressive, metastatic disease," Dr. Chodosh explained. "Surprisingly, we’ve found that certain drugs that don’t work against actively growing cancers can be very effective against these sleeper cells. This tells us that the biology of dormant tumor cells is very different from active cancer cells, opening up new therapeutic avenues."
The preclinical phase of the latest study, conducted by Dr. Chodosh’s team, involved a rigorous series of experiments in mouse models. These studies pinpointed specific mechanisms, namely autophagy and mTOR signaling, as critical pathways that allow tumor cells to maintain their dormant state. By targeting these pathways, the researchers identified two distinct drugs, already approved by the FDA for other medical conditions, that could effectively clear MRD in mice. This intervention led to significantly longer survival times without cancer recurrence in the animal models, providing robust evidence for the clinical potential of this strategy. The use of repurposed drugs offers a significant advantage, as their safety profiles and pharmacokinetic properties are already well-established, potentially accelerating their path to clinical application.
The CLEVER Trial: Translating Science into Patient Benefit
Following the compelling preclinical results, the research transitioned to a randomized phase II clinical trial, named CLEVER, led by principal investigator Angela DeMichele, MD, MSCE, FASCO, the Mariann T. and Robert J. MacDonald Professor in Breast Cancer Research. The trial was meticulously designed to evaluate the safety and efficacy of targeting dormant cells in human breast cancer survivors.
The initial phase of the CLEVER study involved screening breast cancer survivors who had completed their primary treatments within the preceding five years and had clear scans, indicating no active disease. A critical component of this screening was the collection of bone marrow samples, which were then rigorously analyzed to detect the presence of dormant tumor cells. This innovative approach allowed researchers to precisely identify the subset of survivors who harbored these high-risk cells.
For patients identified with dormant tumor cells, eligibility opened for enrollment in the therapeutic arm of the Phase II CLEVER trial. Participants were then randomized into one of three treatment arms: monotherapy with one of the two study drugs, monotherapy with the other study drug, or combination therapy with both drugs. Each patient received six cycles of their assigned therapy. The results were remarkably encouraging: the treatment successfully cleared dormant tumor cells from an impressive 80 percent of the study participants within six to twelve months.
After a median follow-up period of 42 months (3.5 years), the clinical outcomes were even more striking. The three-year survival rate without any disease recurrence was above 90 percent in patients who received monotherapy with one of the study drugs, and a remarkable 100 percent for patients who received the combination of both study drugs. Out of the 51 breast cancer survivors enrolled in the trial, only two experienced a cancer recurrence during the follow-up period. This low recurrence rate, particularly in a cohort identified as high-risk, underscores the profound potential of this preventative strategy.
"The lingering fear of cancer returning is something that hangs over many breast cancer survivors after they celebrate the end of treatment," Dr. DeMichele noted. "Right now, we just don’t know when or if someone’s cancer will come back – that’s the problem we set out to solve. Our study shows that preventing recurrence by monitoring and targeting dormant tumor cells is a strategy that holds real promise, and I hope it ignites more research in this area." She added, "We want to be able to give patients a better option than ‘wait and see’ after they complete breast cancer treatment. We’re encouraged by these results that we’re on the right track."
A Chronology of Progress: From Concept to Clinical Application
The journey to this pivotal trial has been a long and dedicated one, reflecting years of sustained scientific inquiry.
- Early 2000s onwards: Dr. Lewis Chodosh’s laboratory begins fundamental research into tumor cell dormancy, identifying the mechanisms by which cancer cells can survive in a quiescent state and reactivate. This work laid the theoretical groundwork for targeting dormant cells.
- Preclinical Investigations: Over several years, Dr. Chodosh’s team conducts extensive in vitro and in vivo studies, primarily in mouse models, to identify specific pathways (like autophagy and mTOR signaling) critical for dormancy and to screen existing FDA-approved drugs for their ability to clear MRD. This phase meticulously demonstrated the efficacy of repurposed drugs against dormant cells.
- Late 2010s (approx.): The concept of the CLEVER trial is conceived, translating the preclinical successes into a human clinical study design. Securing federal funding from entities like the National Cancer Institute (NCI) and the Department of Defense (DoD) is crucial at this stage.
- Trial Initiation: The Phase II CLEVER clinical trial begins enrollment, meticulously selecting breast cancer survivors and screening them for the presence of dormant cells in their bone marrow.
- Treatment and Monitoring: Eligible patients undergo randomized treatment regimens, followed by rigorous monitoring for cell clearance and, most importantly, recurrence-free survival.
- September 2023: Dr. Angela DeMichele presents interim outcomes data from the CLEVER study at the European Society for Medical Oncology (ESMO) Congress, generating significant excitement within the oncology community.
- Today (Publication Date): The full findings of the Phase II CLEVER trial are published in Nature Medicine, making the detailed results and methodologies available to the global scientific community.
- Present Day: Two larger, subsequent clinical trials, the Phase II ABBY and Phase II PALAVY clinical trials, are actively enrolling patients across multiple cancer centers nationwide to further confirm and expand upon the promising results of the CLEVER study.
Broader Implications and Future Directions
The success of the CLEVER trial holds profound implications for the future of breast cancer care and potentially for other cancer types.
- Revolutionizing Post-Treatment Surveillance: This research paves the way for a proactive, rather than reactive, approach to cancer recurrence. Instead of a "wait and see" strategy, clinicians may soon be able to actively screen for dormant cells and intervene preventatively, dramatically altering the emotional and physical landscape for survivors.
- Advancing Personalized Medicine: The ability to identify patients specifically at high risk due to MRD allows for highly personalized and targeted interventions. This avoids unnecessary treatment for low-risk individuals while ensuring that those most vulnerable receive crucial preventative therapy.
- The Power of Drug Repurposing: The trial’s success with repurposed FDA-approved drugs highlights an efficient and cost-effective pathway for drug development. Utilizing existing medications with known safety profiles can significantly reduce the time and expense associated with bringing new treatments to patients. This strategy could be broadly applicable across oncology.
- New Avenues for Research: The finding that dormant cells have a distinct biology from active cancer cells opens vast new areas for fundamental research into cancer cell plasticity, survival mechanisms, and drug resistance. Understanding these differences could lead to the development of entirely novel classes of anti-cancer agents.
- Economic and Quality of Life Benefits: Preventing recurrence, particularly the onset of incurable metastatic disease, could lead to substantial improvements in patients’ quality of life, reducing the burden of indefinite treatment and the immense psychological stress associated with living with advanced cancer. Furthermore, it could alleviate a significant portion of the economic strain on healthcare systems associated with long-term metastatic cancer care.
While the results are undeniably promising, it is crucial to recognize that the CLEVER study was a Phase II trial involving a relatively small cohort of 51 patients. The ongoing Phase II ABBY and PALAVY trials are vital next steps, designed to confirm these findings in larger, more diverse patient populations and to further refine treatment strategies. If these larger trials yield similar positive outcomes, the path to potential regulatory approval and widespread clinical adoption could be significantly accelerated.
The research was made possible through substantial funding from critical governmental agencies, including the National Cancer Institute (R01CA208273) and the Department of Defense (BC160784), underscoring a national commitment to eradicating cancer. Additional philanthropic and organizational support was provided by the V Foundation, the Breast Cancer Research Foundation, QVC "Shoes on Sale," the Avon Foundation, the Raynier Institute & Foundation, and numerous generous individual donors. This broad base of support highlights the collaborative effort required to translate cutting-edge scientific discoveries into tangible patient benefits.
For breast cancer survivors, this research offers more than just a scientific publication; it represents a tangible beacon of hope that the fear of recurrence might one day be significantly diminished, replaced by effective preventative strategies. The pioneering work at the University of Pennsylvania stands as a testament to the relentless pursuit of innovative solutions in the ongoing fight against cancer. Patients interested in learning more about these or other breast cancer clinical trials at Penn Medicine are encouraged to contact Penn Medicine’s dedicated research team.
