By Billy Candra 
The findings illuminate a critical window of opportunity in breast cancer management: the ability to detect and neutralize residual cancer cells that lie dormant after initial treatment, often for years or even decades. While advancements in detection and therapy have dramatically improved overall breast cancer survival rates globally, the specter of recurrence continues to loom large for millions. When breast cancer returns after initial successful treatment, it often presents as metastatic disease, which remains largely incurable, necessitating continuous and indefinite therapeutic interventions that can only manage, but not eliminate, the cancer entirely. Approximately 30 percent of women and men initially diagnosed with breast cancer will experience a relapse, a statistic that underscores the urgent need for preventative strategies.
The Enduring Challenge of Breast Cancer Recurrence
Breast cancer, a heterogeneous disease, exhibits diverse patterns of recurrence. Aggressive subtypes such as triple-negative breast cancer (TNBC) and HER2-positive (HER2+) breast cancer typically recur within a few years of diagnosis. In contrast, estrogen receptor-positive (ER+) breast cancers, which account for the majority of cases, can exhibit late recurrences, sometimes manifesting decades after initial therapy. This variability in recurrence patterns has made it exceedingly difficult for clinicians to predict who is at highest risk and, more importantly, when to intervene. Until now, there has been no reliable method to identify survivors harboring these dormant cells in real-time or to deploy targeted treatments to prevent an incurable relapse before it takes hold. The psychological burden on survivors, living with the constant apprehension of their cancer returning, is profound. As principal investigator Angela DeMichele, MD, MSCE, FASCO, the Mariann T. and Robert J. MacDonald Professor in Breast Cancer Research, articulated, "The lingering fear of cancer returning is something that hangs over many breast cancer survivors after they celebrate the end of treatment. 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."
Unveiling the "Sleeper Cells" and Their Unique Biology
The groundbreaking study builds upon extensive prior research into the nature of dormant tumor cells, often referred to as "sleeper cells" or minimal residual disease (MRD). These are individual cancer cells or microscopic clusters that survive initial chemotherapy, radiation, or surgery but remain in a quiescent state, undetectable by standard imaging techniques like mammograms, CT scans, or PET scans. Because they are not actively dividing or forming tumors, they do not metabolically signal in a way that allows current diagnostics to spot them. However, under certain conditions, these sleeper cells can reactivate, proliferate, and disseminate throughout the body, ultimately leading to the development of metastatic breast cancer – the primary cause of breast cancer-related mortality. Patients identified with MRD have a significantly higher likelihood of experiencing breast cancer recurrence and, consequently, reduced overall survival.
A crucial foundation for this latest clinical success was the earlier work led by Lewis Chodosh, MD, PhD, chair of Cancer Biology and senior author of the current study. Dr. Chodosh’s team previously identified specific molecular pathways that enable these dormant tumor cells to persist in patients for extended periods, sometimes for decades. This understanding was critical, as it revealed that the biology of dormant cells is distinctly different from that of actively growing cancer cells. Dr. Chodosh emphasized this distinction, stating, "Our research shows that this sleeper phase represents an opportunity to intervene and eradicate the dormant tumor cells before they have the chance to come back as aggressive, metastatic disease. 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." This insight is transformative, suggesting that traditional oncology drug development, which primarily targets actively proliferating cells, may have overlooked effective agents against dormant disease.
In the preclinical phase of the latest research, Dr. Chodosh’s laboratory conducted a comprehensive series of experiments using mouse models of breast cancer. These studies were designed to further elucidate the underlying mechanisms of dormancy and to identify potential therapeutic targets. The team demonstrated that two distinct drugs, already approved by the FDA for other medical conditions, could effectively clear MRD in these animal models. This clearance led to a significant increase in cancer recurrence-free survival in the treated mice. The identified drugs targeted critical cellular pathways: autophagy and mTOR signaling. The researchers found that these pathways were pivotal in allowing tumor cells to maintain their dormant state, essentially providing a survival mechanism that could be disrupted by the repurposed drugs. The ability to repurpose existing, FDA-approved drugs is a significant advantage, potentially accelerating their transition to clinical use by bypassing much of the lengthy and costly early-stage drug development and safety testing.
The CLEVER Trial: A New Hope for Survivors
Translating these compelling preclinical findings into a human clinical trial, Dr. DeMichele’s team initiated the Phase II CLEVER trial (Clinical Lymph Node and ER-Positive Breast Cancer Evaluation of Recurrence). The trial was designed to evaluate the safety and efficacy of targeting dormant cells in breast cancer survivors. The initial step involved screening breast cancer survivors who had completed their primary treatment within the last five years and had clear imaging scans. These individuals, ostensibly cancer-free, underwent a specialized screening procedure: a bone marrow biopsy. Bone marrow is a known reservoir for dormant cancer cells, making it an ideal site for detecting MRD that is otherwise invisible.
If dormant tumor cells were detected in a participant’s bone marrow, they became eligible to enroll in the randomized Phase II CLEVER clinical trial. A total of 51 breast cancer survivors were randomized into different treatment arms. Participants received either monotherapy with one of the two study drugs (identified in preclinical studies) or combination therapy with both drugs. The treatment regimen consisted of six cycles. The primary objective was to determine if these repurposed drugs could effectively clear dormant tumor cells. The results were remarkably positive: existing drugs were able to clear dormant tumor cells from an impressive 80 percent of the study participants.
The long-term outcomes for these participants were even more encouraging. After a median follow-up period of 42 months (approximately 3.5 years), the three-year survival rate without any disease recurrence was above 90 percent in patients who received one drug, and a perfect 100 percent for patients who received both study drugs in combination. Critically, only two patients on the entire study experienced a cancer recurrence during the follow-up period, a stark contrast to the 30% recurrence rate seen in the general breast cancer survivor population. These figures represent a profound improvement in preventing recurrence and suggest a paradigm shift in post-treatment management.
Implications and Future Directions
The success of the CLEVER trial carries immense implications for the future of breast cancer care. It offers a tangible pathway to move beyond the current "wait and see" approach, which leaves survivors in perpetual anxiety, towards a proactive, preventative strategy. Dr. DeMichele highlighted this shift, stating, "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." This breakthrough has the potential to dramatically improve the quality of life for millions of breast cancer survivors by mitigating the devastating physical and emotional toll of recurrence.
From a broader perspective, this research could pave the way for a new era of personalized medicine in oncology. Identifying patients at high risk of recurrence through MRD detection allows for targeted intervention, avoiding unnecessary treatment for those at low risk while providing crucial protection for those most vulnerable. The use of repurposed, FDA-approved drugs is also a significant advantage, potentially shortening the timeline for clinical translation and reducing the colossal costs typically associated with developing new pharmaceutical agents. This approach could make these preventative therapies more accessible and affordable sooner.
The oncology community is expected to greet these findings with considerable optimism. Patient advocacy groups are likely to champion this research as a beacon of hope for survivors. While the results from a Phase II trial are highly promising, larger, multicenter Phase III clinical trials will be necessary to definitively confirm these findings, establish long-term efficacy, and identify any rare side effects of extended treatment.
Acknowledging this necessity, the Penn team is already actively enrolling patients in two larger, ongoing studies designed to confirm and extend the results of the CLEVER study. These are the Phase II ABBY clinical trial and the Phase II PALAVY clinical trial, both of which are available at multiple cancer centers across the country. These next-stage trials will be crucial for validating the findings in a more diverse patient population and for gathering additional data on optimal dosing, duration of treatment, and the long-term impact on recurrence rates and overall survival.
This pivotal research was made possible through robust financial backing from several key organizations, including the National Cancer Institute (R01CA208273) and the Department of Defense (BC160784). Additional significant support was provided by philanthropic organizations such as the V Foundation, the Breast Cancer Research Foundation, QVC "Shoes on Sale," the Avon Foundation, the Raynier Institute & Foundation, and numerous generous individual philanthropic donations. The widespread support underscores the recognized importance and potential impact of this line of research. Notably, Dr. DeMichele had previously presented interim outcomes data from the study at the European Society for Medical Oncology (ESMO) Congress 2023, signaling the growing excitement and anticipation within the global oncology community for these results.
For breast cancer survivors and their families, this research offers a tangible promise: that the end of initial treatment may no longer be just the beginning of a watchful waiting period, but rather an opportunity to proactively secure a future free from the fear and reality of recurrence. Patients interested in learning more about these or other breast cancer clinical trials at Penn Medicine are encouraged to contact [email protected] for further information and guidance.
