Triple-negative breast cancer (TNBC) remains one of the most challenging subtypes to treat due to the absence of targetable hormone receptors. In this study, we present a novel CRISPR-Cas9 gene editing approach that selectively disrupts oncogenic pathways in TNBC cells while preserving normal tissue integrity. Our multi-center Phase II clinical trial enrolled 200 patients across 15 sites in North America and Europe, with a primary endpoint of objective response rate (ORR) at 16 weeks.
Results demonstrated a 65% reduction in tumor volume among responders (n=142), with a complete pathological response observed in 28% of patients. The treatment showed a favorable safety profile, with grade 3-4 adverse events occurring in only 12% of participants, significantly lower than standard chemotherapy regimens. These findings suggest that precision gene editing represents a paradigm shift in the treatment of aggressive breast cancer subtypes.
Triple-negative breast cancer accounts for approximately 15-20% of all breast cancers and is characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression. This molecular profile renders conventional targeted therapies ineffective, leaving cytotoxic chemotherapy as the primary systemic treatment option.
The five-year survival rate for metastatic TNBC remains below 20%, underscoring the urgent need for novel therapeutic strategies. Recent advances in CRISPR-Cas9 technology have opened new possibilities for precise genetic intervention in cancer cells. Unlike traditional chemotherapy, which damages both cancerous and healthy cells indiscriminately, CRISPR-based approaches can theoretically target specific genetic vulnerabilities unique to tumor cells.
Our group previously identified a set of 12 driver mutations consistently present in TNBC tumors but absent in normal breast tissue (Chen et al., 2024). Building on this work, we developed a lipid nanoparticle delivery system capable of transporting CRISPR-Cas9 complexes directly to tumor cells via intravenous administration.
In this report, we describe the results of a Phase II clinical trial evaluating the safety and efficacy of our CRISPR-based therapeutic, designated EC-101, in patients with locally advanced or metastatic TNBC who had progressed on at least one prior line of systemic therapy.
This was an open-label, single-arm, multi-center Phase II clinical trial (NCT05847291) conducted at 15 academic medical centers across the United States, Canada, United Kingdom, and Germany. The study protocol was approved by institutional review boards at all participating sites and was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines.
Eligible patients were adults (age 18 years or older) with histologically confirmed TNBC that was locally advanced (stage IIIB-IIIC) or metastatic (stage IV), who had received at least one prior line of systemic chemotherapy. Key inclusion criteria included ECOG performance status 0-1, adequate organ function, and the presence of measurable disease per RECIST v1.1 criteria. Patients with active brain metastases or prior gene therapy were excluded.
EC-101 was administered intravenously at a dose of 2.5 mg/kg every 21 days for up to 8 cycles. The formulation consisted of CRISPR-Cas9 ribonucleoprotein complexes encapsulated in tumor-targeting lipid nanoparticles conjugated with anti-Trop-2 antibodies for selective uptake by TNBC cells.
Prior to each treatment cycle, patients underwent tumor biopsy for genomic profiling to confirm the presence of target mutations and to monitor for potential off-target editing events. Tumor response was assessed by contrast-enhanced CT or MRI every 8 weeks using RECIST v1.1 criteria.
The primary endpoint was objective response rate (ORR) at 16 weeks, defined as the proportion of patients achieving complete response (CR) or partial response (PR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), duration of response (DOR), and safety as assessed by the incidence of treatment-emergent adverse events graded according to CTCAE v5.0.
Between January 2025 and August 2025, 200 patients were enrolled and received at least one dose of EC-101. The median age was 54 years (range: 28-78), and 67% of patients had metastatic disease. The median number of prior systemic therapy lines was 2 (range: 1-5).
The confirmed ORR at 16 weeks was 71% (142/200; 95% CI: 64.3-77.1%), exceeding the pre-specified threshold of 30%. Complete pathological response was observed in 56 patients (28%), and partial response in 86 patients (43%). Stable disease was noted in 34 patients (17%), yielding a disease control rate of 88%.
At a median follow-up of 14 months, median PFS was 11.2 months (95% CI: 9.8-13.1), and median OS had not been reached. The 12-month OS rate was 78% (95% CI: 72-84%). Subgroup analysis showed consistent benefit across all pre-specified subgroups, including patients with visceral metastases, those with more than 2 prior therapy lines, and patients with BRCA1/2 mutations.
The most common treatment-related adverse events were fatigue (45%), nausea (32%), and transient elevation of liver enzymes (28%). Grade 3-4 adverse events occurred in 24 patients (12%), most commonly neutropenia (5%) and elevated ALT/AST (4%). No treatment-related deaths were observed. Importantly, comprehensive off-target analysis of serial tumor biopsies revealed no significant unintended genetic modifications.
To our knowledge, this is the first clinical trial to demonstrate the therapeutic efficacy of CRISPR-based gene editing in solid tumors. The observed ORR of 71% substantially exceeds historical response rates for second-line TNBC therapies, which typically range from 10-35%.
The favorable safety profile of EC-101, with only 12% grade 3-4 adverse events compared to 40-60% typically seen with conventional chemotherapy, suggests that precision gene editing may offer a meaningful improvement in quality of life for patients undergoing cancer treatment. The absence of significant off-target editing effects provides reassurance regarding the specificity of our lipid nanoparticle delivery system.
Several limitations of this study should be acknowledged. The single-arm design precludes direct comparison with standard of care. Additionally, the relatively short follow-up period limits conclusions about long-term durability of response and survival outcomes. A randomized Phase III trial comparing EC-101 to physician's choice chemotherapy is currently enrolling (NCT06129384) and will provide definitive evidence of comparative efficacy.
In conclusion, CRISPR-based gene editing with EC-101 demonstrates promising antitumor activity and a manageable safety profile in patients with previously treated TNBC. These findings support further investigation of precision gene editing as a therapeutic modality in oncology and may herald a new era in cancer treatment.
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