Merck KGaA Wins FDA Approval for Pimjetmi, Entering a Competitive Rare Tumor Treatment Market

November 12, 2026

Merck KGaA has secured US Food and Drug Administration (FDA) approval for Pimjetmi (pimicotinib), a once-daily oral targeted therapy for adults with symptomatic tenosynovial giant cell tumor (TGCT). The approval, announced on November 10, 2026, introduces another systemic treatment option for patients whose tumors cannot be safely managed through surgery because of the risk of worsening functional limitations or severe complications.

Pimjetmi is a selective colony-stimulating factor 1 receptor (CSF-1R) inhibitor. Its approval is based on results from the Phase III MANEUVER clinical trial, which demonstrated a significant improvement in tumor response, joint mobility, physical functioning and pain compared with placebo.

The development strengthens Merck KGaA's rare tumor portfolio and places the company in direct competition with established CSF-1R therapies from Ono Pharmaceutical and Daiichi Sankyo.

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Understanding Tenosynovial Giant Cell Tumor

Tenosynovial giant cell tumor is a rare, locally aggressive tumor that develops in the synovial tissue surrounding joints and tendon sheaths. It most commonly affects joints such as the knee, hip, ankle, wrist and shoulder.

TGCT is generally classified into two major forms:

• Localized TGCT: Usually affects a limited area within or around a joint.

• Diffuse TGCT: Involves a larger area of synovial tissue and can be more difficult to manage because of its extensive growth and recurrence risk.

Although TGCT is generally considered non-malignant, it can cause significant physical impairment. Patients may experience persistent joint pain, swelling, stiffness, reduced mobility and difficulty performing everyday activities.

Surgery has traditionally been the primary treatment approach. However, complete tumor removal may be difficult in diffuse cases or when the tumor is located close to important structures within a joint.

Repeated surgery can also increase the risk of joint damage, functional limitations and recurrence. This creates a need for systemic treatments that target the biological mechanisms responsible for tumor growth.

Why CSF-1R Inhibition Matters

The CSF-1R pathway plays an important role in TGCT development.

In affected tissue, abnormal production of colony-stimulating factor 1 (CSF-1) attracts and supports the accumulation of macrophages and other inflammatory cells. These cells contribute to the formation and growth of the tumor-associated tissue.

Pimicotinib blocks CSF-1R signalling, reducing the biological activity of cells involved in this process.

This targeted approach aims to reduce tumor volume and associated symptoms without relying exclusively on surgical removal.

The mechanism is particularly relevant for patients with symptomatic disease who face substantial functional risks from surgery.

FDA Approval and Key Clinical Findings

The FDA approved Pimjetmi on November 10, 2026, for adults with symptomatic TGCT for which surgical resection may cause worsening functional limitation or severe morbidity.

The approval was supported by the Phase III MANEUVER trial (NCT05804045), an international, randomized, double-blind, placebo-controlled study.

Patients received pimicotinib 50 mg once daily or placebo. The trial evaluated tumor response and patient-reported and functional outcomes.

Major MANEUVER Trial Results

The FDA reported an objective response rate of 56% for pimicotinib compared with 3.2% for placebo at Week 25. The assessment was conducted through blinded independent central review using RECIST 1.1 criteria.

The median duration of response had not been reached in the pimicotinib treatment group at the time of the FDA assessment. Among patients who achieved a response, 91% maintained it for at least six months and 77% for at least 12 months.

These results indicate that tumor shrinkage was sustained in many responding patients during the available follow-up period. They do not establish a cure or guarantee long-term disease control for every patient.

Improvements in Physical Function and Pain

The clinical findings extend beyond tumor shrinkage.

Patients receiving pimicotinib demonstrated statistically significant improvements across several prespecified clinical outcomes at Week 25:

• Joint mobility: Improvements in active range of motion in the affected joint.

• Pain reduction: Lower worst-pain scores measured through the Brief Pain Inventory.

• Physical functioning: Improvements in patient-reported physical function measured through the PROMIS Physical Function assessment.

These outcomes are important because TGCT can affect patients' mobility and everyday activities even when the disease does not spread to distant organs.

For physicians, improvements in joint function and pain provide additional information when evaluating the clinical value of a treatment.

Safety Profile and Regulatory Considerations

Pimjetmi demonstrated a manageable safety profile in its clinical development programme, but treatment requires monitoring.

According to the FDA, the most common adverse reactions occurring in more than 20% of patients included:

• Pruritus

• Rash

• Facial edema

• Periorbital edema

• Fatigue

• Nausea

• Headache

• Peripheral edema

Common laboratory abnormalities included increases in creatine phosphokinase, lactate dehydrogenase, AST, ALT, lipase, amylase and cholesterol.

The FDA prescribing information includes warnings and precautions for hepatotoxicity, embryo-fetal toxicity and increased serum creatinine without affecting renal function.

The recommended dosage is 50 mg orally once daily, with or without food.

Why Liver Safety Matters

Liver safety is an important consideration in the TGCT treatment category because an earlier CSF-1R inhibitor, Turalio (pexidartinib), carries a boxed warning for serious and potentially fatal liver injury, including vanishing bile duct syndrome.

Turalio is also subject to a restricted Risk Evaluation and Mitigation Strategy (REMS) programme.

Pimjetmi's approval does not mean that it is free from hepatotoxicity risk. Its own prescribing information includes a hepatotoxicity warning. However, its clinical and regulatory safety profile will be evaluated in the context of the specific risks, monitoring requirements and treatment outcomes associated with each available therapy.

For physicians, the selection of a CSF-1R inhibitor will depend on individual patient characteristics, safety considerations, treatment response and monitoring requirements.

Competitive Landscape: Three FDA-Approved CSF-1R Therapies

Pimjetmi enters a specialised treatment category that already includes two approved therapies: Turalio and Romvimza.

1. Daiichi Sankyo: Turalio

Turalio was the first CSF-1R inhibitor approved by the FDA for selected adults with symptomatic TGCT in 2019.

Its approval established an important systemic treatment option for patients whose disease could not be adequately managed through surgery.

However, serious liver injury is a major safety concern. Its boxed warning and REMS requirements create additional monitoring and prescribing considerations for healthcare professionals.

2. Ono Pharmaceutical: Romvimza

Romvimza (vimseltinib) received FDA approval in February 2025. The treatment was developed by Deciphera Pharmaceuticals, which was acquired by Ono Pharmaceutical in 2024.

Its approval was supported by the Phase III MOTION trial, which demonstrated an objective response rate of 40% compared with 0% for placebo at Week 25.

Romvimza provides another targeted treatment option for adults with symptomatic TGCT when surgery may cause worsening functional limitations or severe morbidity.

The product is administered orally at 30 mg twice weekly, with at least 72 hours between doses.

3. Merck KGaA: Pimjetmi

Pimjetmi adds a third treatment option to this category.

Its Phase III MANEUVER trial demonstrated a 56% objective response rate at Week 25 compared with 3.2% for placebo.

The once-daily oral dosing schedule, response durability and improvements in pain and physical functioning are relevant factors for physicians evaluating treatment options.

However, response rates from different clinical trials should not be interpreted as direct comparative evidence. MANEUVER and MOTION were separate studies with different trial designs and patient populations. A head-to-head trial would be needed to establish comparative efficacy.

Merck KGaA's Rare Tumor Strategy

The Pimjetmi approval is part of Merck KGaA's broader effort to strengthen its oncology and rare disease portfolio.

In July 2025, Merck KGaA completed its acquisition of SpringWorks Therapeutics for an enterprise value of approximately $3.4 billion, equivalent to around €3 billion. The transaction had an equity value of approximately $3.9 billion.

The acquisition expanded Merck's rare tumor portfolio through products including:

• Ogsiveo (nirogacestat): Approved for adults with progressing desmoid tumors who require systemic treatment.

• Gomekli (mirdametinib): Approved for adults and children with neurofibromatosis type 1-associated plexiform neurofibromas.

Pimicotinib, however, came through a separate licensing agreement with Abbisko Therapeutics rather than through the SpringWorks acquisition.

Merck initially secured rights to develop and commercialise pimicotinib in selected territories. In March 2025, it exercised an option to obtain worldwide commercialisation rights.

Under the agreement, Abbisko is eligible for regulatory and commercial milestone payments and tiered royalties on net sales.

This arrangement demonstrates how pharmaceutical companies can expand specialised oncology portfolios through external licensing alongside acquisitions and internal research.

Commercial Opportunities and Challenges

The FDA approval creates commercial opportunities across the TGCT treatment ecosystem. However, successful adoption will depend on more than regulatory clearance.

1. Physician Adoption and Treatment Positioning

Merck must establish Pimjetmi's role within existing TGCT treatment pathways.

Orthopedic oncologists, orthopedic surgeons, rheumatologists and specialised oncology centres will be important stakeholders.

Physicians will assess the product's response data, safety profile, dosing schedule and suitability for individual patients.

2. Market Access and Reimbursement

Pimjetmi will need appropriate reimbursement and formulary access across US healthcare settings.

Commercial success will depend on payer evaluations, specialty pharmacy access, patient support programmes and the ability to demonstrate clinical value.

3. Competitive Differentiation

Merck must communicate the clinical evidence supporting Pimjetmi while avoiding unsupported claims of superiority over existing treatments.

Relevant differentiation factors include:

• Objective response and duration of response.

• Improvements in joint mobility and pain.

• Daily dosing and treatment convenience.

• Safety monitoring requirements.

• Long-term clinical outcomes.

4. Long-Term Clinical Evidence

Longer follow-up will help establish the durability of response, long-term safety and impact on disease management.

Real-world evidence may also help assess treatment persistence, patient experience and outcomes across broader clinical populations.

5. International Commercialisation

The FDA review was conducted under Project Orbis, involving collaboration with regulatory authorities in Australia, Canada, Israel, Switzerland and the United Kingdom, with the European Medicines Agency participating as an observer.

Project Orbis supports coordinated oncology regulatory reviews, but it does not mean that every participating authority automatically approves a medicine at the same time.

Merck's international strategy will depend on individual regulatory decisions, local reimbursement and commercial access.

What This Development Means for the Pharmaceutical Industry

Pimjetmi's approval highlights several broader trends in rare disease drug development.

Targeted therapies for rare tumors: CSF-1R inhibition demonstrates how understanding disease biology can support systemic treatment development in conditions historically managed primarily through surgery.

Licensing-led portfolio expansion: Merck's partnership with Abbisko illustrates how established pharmaceutical companies can access specialised drug candidates through external innovation.

Clinical outcomes beyond tumor response: Improvements in pain, mobility and physical function are increasingly important when assessing treatment value in diseases that affect everyday activities.

Competition within specialised indications: The presence of three approved CSF-1R therapies creates a more developed treatment category, increasing the importance of clinical differentiation, safety evidence and market access strategy.

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Conclusion

The FDA approval of Pimjetmi represents an important addition to the treatment landscape for symptomatic TGCT. Its Phase III MANEUVER results demonstrated meaningful tumor responses alongside improvements in joint mobility, pain and physical functioning.

For Merck KGaA, the next challenge is to establish Pimjetmi's commercial position against Turalio and Romvimza while building physician confidence in its clinical benefits and safety profile.

For the wider pharmaceutical industry, the development reinforces the value of targeted drug development, external licensing and specialised rare tumor portfolios.

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