A Paradigm Shift in Desmoid Tumor Management
For decades, the management of desmoid tumors (DTs)—also known as aggressive fibromatosis—has been a clinical conundrum. While histologically benign and non-metastasizing, these mesenchymal neoplasms are characterized by an unpredictable clinical course, local invasiveness, and a high propensity for recurrence. The treatment landscape has shifted from aggressive surgical resection, which often led to high morbidity and recurrence rates, toward more conservative ‘watch-and-wait’ strategies and systemic interventions. However, for patients with advanced, symptomatic, or refractory disease, the need for effective and tolerable systemic therapy remains acute.
A landmark Phase 3 investigator-initiated trial, recently published in Clinical Cancer Research, provides compelling evidence for the efficacy of pegylated liposomal doxorubicin (PLD) in this patient population. Led by Xu et al., the study demonstrates that PLD offers a dramatic improvement in progression-free survival (PFS) and objective response rates, potentially establishing it as a preferred systemic option for patients who have failed prior therapies or require rapid disease control.
Study Highlights
The trial’s findings are characterized by several key clinical metrics:
1. PLD reduced the risk of disease progression or death by 95% compared to placebo, with a hazard ratio (HR) of 0.05.
2. The 2-year progression-free survival rate was 90.4% in the PLD group versus 19.6% in the placebo group.
3. A confirmed objective response rate (ORR) of 40.4% was observed with PLD, compared to just 4.3% with placebo.
4. The safety profile was manageable, with grade 3 or higher adverse events primarily limited to hematologic toxicities and mucositis.
The Clinical Challenge of Desmoid Tumors
Desmoid tumors arise from the proliferation of well-differentiated fibroblasts and are frequently associated with mutations in the CTNNB1 gene (encoding beta-catenin) or the APC gene. These mutations lead to the stabilization of beta-catenin, driving the transcription of genes involved in cell proliferation and survival.
In clinical practice, DTs present a unique challenge. Their growth can be indolent, spontaneously regressive, or rapidly progressive, invading vital structures and causing debilitating pain or functional impairment. For refractory cases—those that continue to grow despite observation or initial systemic treatments like non-steroidal anti-inflammatory drugs (NSAIDs) or hormonal therapies—the choice of second- or third-line therapy has historically been debated. While tyrosine kinase inhibitors (TKIs) like nirogacestat or sorafenib have shown efficacy, the role of cytotoxic chemotherapy, particularly PLD, has required validation through high-level, placebo-controlled evidence.
Trial Architecture: The Phase 3 Design
This investigator-initiated, double-blind, randomized Phase 3 trial was designed to rigorously evaluate PLD against a placebo. Between November 2020 and March 2023, the researchers enrolled 73 patients with advanced or refractory DTs.
Patient Population and Randomization
Patients were randomized in a 2:1 ratio to receive either PLD (49 patients) or a placebo (24 patients). Inclusion criteria focused on those with progressive or symptomatic disease that was considered refractory to standard management. The study design allowed for a crossover from the placebo group to the PLD group upon documented disease progression, ensuring that all participants eventually had access to active treatment if their condition worsened.
Intervention and Endpoints
PLD was administered intravenously at a dose of 50 mg/m² every four weeks for a total of six cycles. This dosing schedule is consistent with protocols used in other oncological indications, such as ovarian cancer or Kaposi sarcoma. The primary endpoint was progression-free survival (PFS), as determined by RECIST v1.1 criteria. Secondary endpoints included objective response rate (ORR), safety, and patient-reported outcomes.
Efficacy Results: Unprecedented Progression-Free Survival
The results of the trial were striking. With a median follow-up of 16.1 months, the median PFS for the PLD group had not yet been reached, while the median PFS for the placebo group was only 4.3 months.
The hazard ratio of 0.05 (95% CI, 0.01–0.17; P < 0.001) represents one of the most significant effect sizes seen in recent connective tissue oncology trials. Subgroup analyses further confirmed that the benefits of PLD were consistent across various demographic and clinical categories, including age, tumor location, and prior treatment history.
Objective Response and Crossover Dynamics
Beyond delaying progression, PLD demonstrated a robust ability to shrink tumors. The confirmed ORR was 40.4% in the PLD arm, compared to 4.3% in the placebo arm (P = 0.002). Most responses were partial, reflecting the fibrotic nature of these tumors, which often stabilize rather than disappear completely. The durability of these responses was a notable feature of the trial, with many patients maintaining disease control long after the six-cycle treatment course was completed.
Safety and Tolerability Profile
Safety is a critical consideration in the treatment of DTs, as these patients often require long-term management and have a near-normal life expectancy. The trial reported that PLD was generally well-tolerated, though it was associated with specific toxicities inherent to liposomal doxorubicin.
Common grade 3 or higher adverse events in the PLD group included:
1. Decreased neutrophil count (10.6%)
2. Oral mucositis (6.4%)
3. Decreased white blood cell count (4.3%)
Hand-foot syndrome (palmar-plantar erythrodysesthesia), a classic side effect of PLD, was observed but managed through dose modifications or supportive care. Importantly, the researchers noted significant differences in patient-reported toxicities between the groups, highlighting the need for clinician vigilance in managing the symptomatic burden of chemotherapy. However, the limited duration of treatment (six cycles) helped mitigate long-term cumulative toxicity, such as cardiotoxicity, which is a concern with traditional anthracyclines but is less frequent with the liposomal formulation at these cumulative doses.
Expert Commentary: Contextualizing the Findings
The results of this trial are likely to influence international guidelines for the treatment of desmoid tumors. Historically, the use of PLD was supported by retrospective series and small Phase 2 trials. By providing Level 1 evidence of its efficacy, this study positions PLD as a formidable competitor to other systemic options.
PLD versus Tyrosine Kinase Inhibitors
One of the most important discussions following this trial involves how to sequence PLD relative to TKIs like nirogacestat, which recently received FDA approval for DTs. TKIs offer the advantage of oral administration and have also shown impressive PFS benefits. However, PLD may be preferred in cases where rapid tumor shrinkage is required or when patients have contraindications to specific TKIs. The high ORR seen in this trial (40.4%) suggests that PLD is highly effective at inducing cytoreduction.
Mechanistic Insights
From a biological perspective, the efficacy of PLD in DTs may be attributed to the ‘enhanced permeability and retention’ (EPR) effect. The fenestrated vasculature often found in aggressive mesenchymal tumors allows the small liposomes to extravasate and accumulate preferentially within the tumor tissue, delivering a high concentration of doxorubicin while minimizing systemic exposure to healthy tissues.
Conclusion and Summary
The Phase 3 trial of pegylated liposomal doxorubicin for advanced and refractory desmoid tumors represents a major step forward in sarcoma oncology. By demonstrating a 95% reduction in the risk of progression and a high rate of durable objective responses, the study confirms that PLD is a highly effective intervention for patients who have exhausted other options.
Key takeaways for clinicians include:
1. PLD should be considered a standard-of-care systemic therapy for progressive or symptomatic DTs.
2. The treatment regimen of 50 mg/m² every four weeks for six cycles provides a favorable balance between efficacy and toxicity.
3. Careful monitoring for hematologic toxicity and mucositis is essential during the treatment period.
As we move toward a more personalized approach to desmoid tumor management, the integration of high-quality data from trials like this will allow clinicians to better tailor therapy to the individual needs of the patient, balancing the goals of tumor control, symptom relief, and quality of life.
References
Xu H, Hu J, Zhang Y, et al. Phase 3 Trial of Pegylated Liposomal Doxorubicin for Patients with Advanced and Refractory Desmoid Tumors. Clin Cancer Res. 2026 Jan 8. doi: 10.1158/1078-0432.CCR-25-3128. PMID: 41504634.
