SARC041 and Abemaciclib Deliver a Long-Awaited Answer in Dedifferentiated Liposarcoma

Dedifferentiated liposarcoma (DDLS) is one of the most treatment-resistant soft tissue sarcomas, and for decades, systemic therapy options have offered only modest benefit. Approved agents such as trabectedin (Yondelis; Janssen Products, LP) and eribulin (Halaven; Eisai Inc) yield a median progression-free survival (mPFS) of just 2.2 and 2.0 months, respectively—a sobering reality for patients with recurrent or metastatic disease.

Three prior phase 3 trials in DDLS—selinexor (Xpovio; Karyopharm Therapeutics Inc) vs placebo, milademetan (Rain Oncology) vs trabectedin, and brigimadlin (Boehringer Ingelheim) vs doxorubicin—all failed to demonstrate a meaningful improvement over the comparator. Results from the SARC041 phase 3 trial (NCT04967521), presented at the 2026 American Society of Clinical Oncology Annual Meeting, mark a meaningful departure from that landscape: abemaciclib (Verzenio; Eli Lilly and Company), a selective CDK4/6 inhibitor, demonstrated a statistically significant improvement in PFS compared with placebo, supporting its potential as a new standard of care in this rare and difficult-to-treat disease.

Understanding Liposarcoma and Its Subtypes

Liposarcoma is a malignant tumor of adipocytic tissue and one of the most common subtypes within the broad category of soft tissue sarcomas, which account for roughly 1% of adult cancers. The disease most often arises in the retroperitoneum or extremities, and while it encompasses several distinct subtypes, they are not clinically or biologically interchangeable.¹

Well-differentiated liposarcoma (WDLS) is low-grade, slow-growing, and rarely metastasizes, though it frequently recurs locally—particularly in the retroperitoneum. DDLS, the focus of SARC041, is a more aggressive entity: a high-grade component that arises in the background of WDLS and carries a substantially higher risk of local recurrence and distant metastasis. Myxoid/round cell liposarcoma and pleomorphic liposarcoma round out the major subtypes, each with distinct molecular drivers and clinical behavior. ¹

What unifies WDLS and DDLS at the molecular level—and what makes DDLS a compelling therapeutic target—is the near-universal co-amplification of CDK4 and MDM2 on chromosome 12q. CDK4 drives cell-cycle progression from G1 to S phase, providing a strong rationale for CDK4 inhibition. MDM2, a negative regulator of p53, has been the target of experimental inhibitors, including milademetan and brigimadlin—both of which failed to outperform comparators in phase 3 trials. The CDK4/MDM2 co-amplification also makes DDLS a model disease for studying senescence biology.¹

The Biological Rationale

The foundation for testing a CDK4/6 inhibitor in DDLS is firmly rooted in the disease’s molecular biology. CDK4 amplification is a near-universal feature of dedifferentiated liposarcoma, making it one of the most clearly defined oncogenic drivers in any solid tumor. This led Mark A. Dickson, MD, associate attending physician specializing in sarcomas at Memorial Sloan Kettering Cancer Center and a lead investigator on SARC041, and colleagues to investigate the potential use of CDK4/6 inhibitors in this population.^1,2

“We identified CDK4 amplification as a defining feature of dedifferentiated liposarcoma—it became an early-career focus for me,” Dickson told Pharmacy Times. “I started a phase 1 treatment in 2006 as a fellow, moved to phase 2 in 2010, and we’ve really been pushing at this for a long time.”²

That persistence paid off in the phase 2 setting, where palbociclib (Ibrance; Pfizer Inc) yielded an mPFS of 4.2 months, and abemaciclib improved that further to 7.7 months. According to Dickson, abemaciclib was favored due to its lower risk of neutropenia, which allows for continuous daily dosing and target suppression in cancer cells.^1,2

Investigating Abemaciclib in a New Setting

SARC041 was a randomized, double-blind, placebo-controlled phase 3 study conducted across 9 academic sarcoma centers in the United States, enrolling 108 patients between December 2021 and September 2024. Eligible patients had recurrent or metastatic DDLS with documented disease progression by RECIST 1.1 within 6 months of study entry—a design choice intended to exclude indolent cases. Patients could have received any number of prior systemic therapies, including none.^1,3 Those with purely WDLS were excluded.

Patients were stratified by prior lines of therapy and randomly assigned 1:1 to abemaciclib 200 mg orally twice daily on a continuous dosing schedule or matching placebo. Scans were performed every 6 weeks, and patients who progressed on placebo were permitted to cross over to open-label abemaciclib. The primary end point was PFS; secondary end points included ORR, post-crossover PFS and response, and overall survival (OS).^1,3

Notably, the control arm used placebo rather than doxorubicin. Doxorubicin carries substantial toxicity and offers only marginal benefit in this setting, and a placebo-controlled design with mandated crossover both ensured ethical access to abemaciclib and allowed a cleaner read of the drug’s intrinsic activity independent of prior chemotherapy.^1,3

Data Reveal Breakthrough Outcomes With Abemaciclib

Abemaciclib demonstrated a statistically significant improvement in PFS at 9.7 months vs 1.5 months for placebo (HR, 0.38; P < .001), representing the strongest PFS signal reported to date in any phase 3 DDLS trial. Among patients receiving abemaciclib as their first line of systemic therapy, the benefit was more pronounced, with mPFS exceeding 16 months. In patients who had received 1 or more prior lines, mPFS was 5.3 months, which was meaningfully better than historical benchmarks.^1,3

The ORR was 9.3% for abemaciclib vs 0% for placebo. While responses were uncommon, Dickson emphasized their significance when they occurred: Among responders, benefit could be profound and durable, including 1 patient with a near-complete response who remained on treatment approximately 4 years after starting therapy.^1,3

Despite 85% of placebo patients crossing over to abemaciclib at progression, an encouraging OS trend emerged. Median OS was not reached in the abemaciclib arm, compared with 25.5 months in the placebo arm (HR, 0.55), though this did not reach statistical significance at the data cutoff. Post-crossover mPFS was 3.4 months, and the ORR was 4%—lower than outcomes in patients starting abemaciclib up front.^1,3

“There are patients with stable disease or partial responses lasting several years, both in the phase 2 study and trending in that direction in the phase 3 data,” Dickson explained. “A meaningful minority can do extremely well for an extended period.”²

The safety profile of abemaciclib in DDLS was consistent with its established profile in breast cancer, primarily myelosuppression and diarrhea, with no new safety signals. Grade 3 to 4 myelosuppression occurred in approximately 30% of patients; grade 3 diarrhea was seen in about 7%. Dose reductions occurred in 39% of abemaciclib patients vs 2% in the placebo arm, suggesting the 200-mg starting dose may be on the higher end for some patients.^1,3

"Even patients who dose reduced to 150 or 100 mg experienced meaningful clinical benefit, so lower doses should not be seen as a failure," Dickson noted.²

SARC041 Moves the Needle in DDLS Care

For a patient population that has watched other cancers be transformed by targeted therapies while their own options barely moved, SARC041 represents a long-overdue inflection point. The trial’s internal validity and statistical strength position abemaciclib as a clinically viable treatment option for DDLS—one that has been available and well characterized in oncology practice for years through its established role in breast cancer.

“We should advocate for inclusion of abemaciclib in treatment guidelines for liposarcoma worldwide,” said Dickson. “Given the benefit of early treatment with abemaciclib, it makes sense to evaluate abemaciclib in the neoadjuvant or adjuvant setting next.”¹

The biomarker program embedded in SARC041, with archival tissue obtained from nearly all phase 3 patients, will continue generating insights well beyond this initial readout, including further investigation of cyclin D amplification as a resistance mechanism. After nearly 2 decades of work, the field finally has a phase 3 winner in dedifferentiated liposarcoma.

REFERENCES

1. Small E, Chein J, Dickson MA, et al. Presented at: 2026 American Society of Clinical Oncology Annual Meeting; May 29-June 2, 2026; Chicago, IL.

2. Dickson MA, Gerlach A. SARC041 and the future of dedifferentiated liposarcoma treatment. Pharmacy Times. May 31, 2026. Accessed May 31, 2026. https://www.pharmacytimes.com/view/sarc041-and-the-future-of-dedifferentiated-liposarcoma-treatment

3. Dickson MA, Ballman KV, Weiss MC, et al. SARC041: a phase 3 randomized double-blind study of abemaciclib versus placebo in patients with advanced dedifferentiated liposarcoma. Presented at: 2026 American Society of Clinical Oncology Annual Meeting; May 29-June 2, 2026; Chicago, IL.