By Billy Candra 
A groundbreaking new study led by researchers at Keck Medicine of USC has potentially unveiled a highly effective combination therapy for glioblastoma, an exceptionally aggressive and often fatal form of brain cancer, which has historically resisted most conventional treatments. This significant development could redefine the treatment landscape for a diagnosis that, according to the National Brain Tumor Society, typically offers patients an average survival of just eight months. The investigation suggests that integrating Tumor Treating Fields (TTFields) therapy with both immunotherapy (specifically pembrolizumab) and standard chemotherapy (temozolomide) can markedly prolong the lives of glioblastoma patients, even those with large, inoperable tumors.
Unlocking Glioblastoma’s Intractable Challenge
Glioblastoma (GBM) stands as the most common and deadliest primary malignant brain tumor in adults. Its notorious aggressiveness stems from several factors: rapid, infiltrative growth that makes complete surgical removal nearly impossible, a high rate of recurrence, and a unique microenvironment that often renders conventional and novel therapies ineffective. The blood-brain barrier, a natural protective mechanism that safeguards the brain from harmful substances in the bloodstream, inadvertently also obstructs many therapeutic agents, including some immunotherapies and chemotherapies, from reaching the tumor effectively. This formidable biological barrier, coupled with the tumor’s inherently immunosuppressive nature, has long presented a major hurdle for medical science.
Standard treatment for newly diagnosed glioblastoma typically involves maximal safe surgical resection, followed by concurrent radiation therapy and chemotherapy with temozolomide, an alkylating agent. This is often followed by adjuvant temozolomide. Despite these aggressive measures, the prognosis remains grim, with median overall survival rarely exceeding 15-20 months, and the vast majority of patients succumbing to the disease within two years. The urgent need for more potent and innovative treatment strategies has been a driving force in neuro-oncology research for decades.
The Novel Therapeutic Alliance: TTFields, Immunotherapy, and Chemotherapy
The promising findings from the Keck Medicine of USC study center on a synergistic approach combining three distinct therapeutic modalities:
- Tumor Treating Fields (TTFields) therapy: A non-invasive, localized treatment that uses alternating electric fields.
- Immunotherapy (Pembrolizumab): An immune checkpoint inhibitor designed to unleash the body’s natural anti-cancer immune response.
- Chemotherapy (Temozolomide): The established standard-of-care chemotherapy for glioblastoma.
This multi-pronged attack aims to overcome glioblastoma’s inherent resistance by simultaneously disrupting tumor cell division, activating and sustaining the immune system’s assault on cancer cells, and directly cytotoxic effects.
Diving Deeper into Tumor Treating Fields (TTFields)
Tumor Treating Fields therapy, marketed as Optune by Novocure, represents a significant innovation in cancer treatment. It was initially approved by the U.S. Food and Drug Administration (FDA) in 2011 for recurrent glioblastoma and subsequently in 2015 for newly diagnosed glioblastoma in combination with temozolomide after standard chemoradiation. The therapy works by delivering low-intensity, intermediate-frequency alternating electric fields directly into tumor cells. These fields are generated by an array of insulated transducer arrays (mesh electrodes) strategically positioned on the patient’s scalp.
At a cellular level, TTFields exert their anti-cancer effect primarily by disrupting mitosis, the process of cell division. The electric fields apply physical forces to key intracellular components, such as tubulin dimers and septin proteins, which are crucial for the formation of the mitotic spindle and cytokinesis. By pushing and pulling these charged components in continually shifting directions, TTFields interfere with proper spindle formation and chromosome segregation, leading to mitotic arrest and ultimately programmed cell death (apoptosis) in rapidly dividing cancer cells. Healthy cells, which divide at a much slower rate or not at all, are largely unaffected, contributing to a generally favorable safety profile compared to systemic therapies. Patients typically wear the electrodes for approximately 18 hours a day, allowing for continuous treatment.
Beyond its direct anti-mitotic effects, the USC study highlights a crucial immune-modulating role of TTFields. Researchers observed that TTFields appear to attract a greater number of tumor-fighting T cells—a type of white blood cell central to adaptive immunity—into and around the glioblastoma. This influx of immune cells is a critical first step in mounting an effective anti-tumor response, especially in an environment typically devoid of such immune activity.
Immunotherapy’s Elusive Promise in Brain Cancer
Immunotherapy, particularly immune checkpoint inhibitors (ICIs) like pembrolizumab (Keytruda), has revolutionized the treatment of numerous cancers, including melanoma, lung cancer, and kidney cancer. Pembrolizumab is an anti-PD-1 antibody that blocks the programmed death-1 (PD-1) receptor on T cells. By doing so, it prevents cancer cells from deactivating T cells via the PD-L1 pathway, thereby "unleashing" the T cells to identify and attack cancerous cells.
Despite its success in other malignancies, immunotherapy, when used as a monotherapy, has largely failed to demonstrate significant efficacy in glioblastoma. This lack of success is primarily attributed to the unique immunosuppressive environment within the glioblastoma tumor and its surrounding brain tissue. As noted, the blood-brain barrier severely restricts the entry of T cells and other immune components into the brain. Furthermore, glioblastomas actively create an immunosuppressive milieu, characterized by the presence of regulatory T cells, myeloid-derived suppressor cells, and inhibitory cytokines, which collectively shield the tumor from immune attack. This creates a "cold" tumor environment, meaning it has few infiltrating immune cells.
David Tran, MD, PhD, chief of neuro-oncology with Keck Medicine, co-director of the USC Brain Tumor Center, and corresponding author of the study, theorized that for immunotherapy to work effectively in glioblastoma, an immune reaction needed to be initiated directly within the tumor itself. This concept, known as in situ immunization, aims to transform the "cold" tumor into a "hot" one, making it susceptible to ICI therapy.
The 2-THE-TOP Phase 2 Trial: Methodology and Breakthrough Findings
The Keck Medicine study analyzed data from the 2-THE-TOP, a multicenter Phase 2 clinical trial (NCT03407223) designed to evaluate the safety and efficacy of this novel triple combination. The trial enrolled 31 newly diagnosed glioblastoma patients who had completed standard chemoradiation therapy. Of these, 26 patients received the full combination of TTFields, chemotherapy (temozolomide), and immunotherapy (pembrolizumab). A particularly high-risk subgroup of seven patients within this cohort had inoperable tumors due to their challenging anatomical locations, representing an especially poor prognosis with limited treatment alternatives.
The treatment protocol involved patients receiving six to 12 monthly cycles of temozolomide alongside TTFields for up to 24 months, with the duration adjusted based on individual patient response. Pembrolizumab was administered intravenously every three weeks, commencing with the second dose of chemotherapy, also for up to 24 months.
The results were striking. Patients who underwent the triple combination therapy demonstrated an approximate 70% increase in overall survival compared to historical controls and patients who had previously received TTFields combined with chemotherapy alone. Specifically, patients in the study lived approximately 10 months longer than historical cohorts receiving TTFields and chemotherapy only.
Even more remarkably, the subgroup of patients with large, inoperable tumors experienced an even greater survival benefit, living approximately 13 months longer than their counterparts in previous studies. These patients also exhibited a much stronger immune activation within their tumors. This counterintuitive finding suggests that larger tumor burden might, in some contexts, provide more antigenic targets for the immune system to recognize and attack once primed by TTFields. This observation challenges conventional wisdom that smaller, resected tumors offer a better prognosis, particularly when considering immune-based therapies.
"Our findings suggest that TTFields may be the key to unlocking the value of immunotherapy in treating glioblastoma," stated Dr. Tran. "By using TTFields with immunotherapy, we prime the body to mount an attack on the cancer, which enables the immunotherapy to have a meaningful effect in ways that it could not before."
Mechanistic Insights: A Synergistic Strategy
The study provides crucial mechanistic insights into how this triple combination therapy achieves its remarkable effect. The researchers observed that TTFields therapy directly contributes to increased infiltration of tumor-fighting T cells into the glioblastoma microenvironment. This influx of T cells effectively transforms the previously "cold" and immunosuppressive tumor into a more "hot" and immunogenic one.
Once TTFields have attracted these crucial T cells, the subsequent administration of immunotherapy (pembrolizumab) becomes far more effective. Pembrolizumab, by blocking the PD-1 checkpoint, ensures these newly recruited T cells remain active longer and are not prematurely deactivated by the tumor’s immune evasion mechanisms. Furthermore, the sustained immune activation leads to the recruitment and development of even stronger, more effective tumor-fighting T cells, creating a positive feedback loop of anti-cancer immunity.
Dr. Tran eloquently summarized this synergistic relationship: "Think of it like a team sport – immunotherapy sends players in to attack the tumor (the offense), while TTFields weaken the tumor’s ability to fight back (the defense). And just like in team sports, the best defense is a good offense." This analogy underscores how TTFields not only directly damages tumor cells but also creates an environment conducive for the immune system to finally engage and effectively combat glioblastoma. The combination effectively bypasses the blood-brain barrier’s immune-blocking effects by initiating the immune response directly within the tumor.
Implications for Patient Care and Prognosis
The results of the 2-THE-TOP Phase 2 trial carry profound implications for glioblastoma patients, particularly for those who currently face the most dire prognoses. The significant extension in overall survival, especially for patients with inoperable tumors, offers a much-needed beacon of hope. For patients whose tumors are deemed surgically unresectable due to size or location, treatment options are severely limited, and quality of life is often poor. This study suggests a potential pathway to not only extend their lives but also to potentially improve their response to subsequent therapies.
"Further studies are needed to determine the optimal role of surgery in this setting, but these findings may offer hope, particularly for glioblastoma patients who do not have surgery as an option," Dr. Tran remarked, highlighting the potential paradigm shift this could represent. While surgical debulking remains a cornerstone of glioblastoma management, these findings hint at a scenario where immune activation, rather than maximal resection, could become the primary driver of therapeutic success in certain patient subgroups. This could lead to a re-evaluation of treatment algorithms and a more personalized approach to glioblastoma care.
Looking Ahead: The Pivotal Phase 3 Trial
Recognizing the immense potential of these Phase 2 findings, Keck Medicine of USC is actively participating in a multicenter, international Phase 3 clinical trial (NCT04471714) to definitively validate the efficacy and safety of TTFields combined with immunotherapy and chemotherapy. Dr. Tran, who has dedicated over a decade to researching TTFields, serves as the chair of the steering committee for this pivotal trial, underscoring the institutional commitment to advancing this research. Frances Chow, MD, a neuro-oncologist with USC Norris Comprehensive Cancer Center, is the principal investigator for the Keck Medicine study site.
This large-scale Phase 3 trial is currently open for enrollment at 28 sites across the United States, Europe, and Israel. The ambitious goal is to enroll over 740 patients through April 2029. Crucially, this trial aims to recruit a diverse patient population, including those with gross total resection, partial resection, or biopsy-only tumors. This comprehensive approach will allow researchers to meticulously assess how the extent of surgical tumor removal influences the immune response and the overall effectiveness of the triple combination therapy, providing a more granular understanding of patient selection and optimal treatment sequencing. The outcome of this Phase 3 trial will be critical in determining whether this promising combination therapy becomes a new standard of care for glioblastoma patients worldwide.
Expert Perspectives and Broader Context
The collaborative nature of this research extends beyond Keck Medicine of USC. Key contributors include Dongjiang Chen, PhD, assistant professor of research neurological surgery; Son Le, PhD, assistant professor of research neurological surgery; Harshit Manektalia, research programmer; Ming Li, PhD, professor of research population and public health sciences; and Adam O’Dell, research lab specialist, all from the Keck School of Medicine of USC. Additionally, Ashley Ghiaseddin, MD, and Maryam Rahman, MD, MS, from the University of Florida, played vital roles in this collaborative effort. This broad scientific partnership reflects the complexity of glioblastoma research and the need for diverse expertise to tackle such a challenging disease.
The National Brain Tumor Society, a leading patient advocacy organization, continually emphasizes the urgent need for more effective treatments for glioblastoma. This study’s findings align with their mission to improve survival and quality of life for patients battling brain tumors, offering a glimmer of hope in a field long plagued by limited options. If validated in Phase 3, this therapy could significantly alter the prognosis for thousands of patients annually.
Funding and Disclosures
This study received funding from a grant provided by Novocure, the company that manufactures Optune, the TTFields device utilized in this research. Dr. David Tran has disclosed receiving honoraria from Novocure for consultant work. Furthermore, Dr. Chen and Dr. Tran are inventors on two patent applications directly related to the work reported in this study. These disclosures are standard practice in medical research and ensure transparency regarding potential conflicts of interest, while not diminishing the scientific rigor or the potential impact of the findings. The scientific community and regulatory bodies will continue to scrutinize the data as the Phase 3 trial progresses, ensuring that any new treatment offers genuine benefit to patients.
