📌 The essentials On June 25, 2026, the FDA approved both Keytruda (pembrolizumab, Merck) and Keytruda Qlex (pembrolizumab and berahyaluronidase alfa-pmph, Merck), each in combination with Trodelvy (sacituzumab govitecan-hziy), for the first-line treatment of adults with unresectable locally advanced or metastatic triple-negative breast cancer (TNBC) whose tumors express PD-L1 with a combined positive score (CPS) at or above 10, as determined by an FDA-authorized test. This is the first FDA-approved regimen pairing a PD-1 inhibitor with a Trop-2-directed antibody-drug conjugate in advanced TNBC. The same combination was approved simultaneously from the Trodelvy side on June 24, 2026 (one day earlier, from Gilead’s filing). The two approvals reflect the same clinical data from the same trial from two different regulatory submissions, one by each company. Clinical basis: Phase 3 ASCENT-04/KEYNOTE-D19 (NCT05382286). 443 patients with first-line PD-L1-positive (CPS at or above 10) metastatic TNBC, randomized to sacituzumab govitecan plus pembrolizumab or sacituzumab govitecan plus physician’s choice chemotherapy plus pembrolizumab. Median PFS 11.2 months versus 7.8 months; HR 0.65 (95% CI 0.51 to 0.84; p=0.0009). ORR 61% versus 55%. OS not reached in either arm. Published in NEJM. What is genuinely new and distinct in this approval: the Keytruda Qlex formulation. Keytruda Qlex is a subcutaneous injection of pembrolizumab co-formulated with berahyaluronidase alfa, a hyaluronidase enzyme that allows the drug to be delivered under the skin rather than through a 30-minute intravenous infusion. Administration time: 1 to 2 minutes, given by a healthcare provider. Setting: any clinical environment with a healthcare provider present, not necessarily an infusion center. The June 25 approval is the first indication where Keytruda Qlex is co-labeled alongside IV Keytruda for a specific combination regimen in breast cancer. NCCN designation: pembrolizumab plus sacituzumab govitecan is a Category 1 preferred first-line option for CPS at or above 10 metastatic TNBC in the NCCN Clinical Practice Guidelines in Oncology for Breast Cancer. PD-L1 testing is required before initiating. Eligible patients must have tumors tested with an FDA-authorized PD-L1 assay showing CPS at or above 10.

Pembrolizumab has been one of the most consequential drugs in oncology since its first approval in 2014. It is now approved for more than 20 types of cancer. It has been part of transformative trials in lung cancer, melanoma, head and neck cancer, cervical cancer, endometrial cancer, urothelial cancer, and now breast cancer at multiple stages. The indication count has grown so large that keeping track of it has become a clinical challenge in its own right.

The June 25, 2026 approval, a new first-line indication in PD-L1-positive metastatic TNBC in combination with sacituzumab govitecan, is meaningful but not entirely surprising given the clinical logic behind it. PD-1 inhibition and Trop-2-directed antibody-drug conjugates target the same disease through distinct mechanisms, and combining them in a population already selected for checkpoint inhibitor responsiveness by PD-L1 expression makes biological sense. The Phase 3 ASCENT-04 trial confirmed that logic with a 35% reduction in progression risk over the prior standard of care.

What makes this approval genuinely worth a dedicated post from the Keytruda angle is not just the new indication. It is the Keytruda Qlex story that sits alongside it, and what a subcutaneous formulation of one of the world’s most-used cancer drugs means for the patients who will receive it for months or years.

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What Pembrolizumab Is and How PD-1 Blockade Works

Pembrolizumab is a humanized monoclonal antibody that targets programmed death receptor-1 (PD-1), a checkpoint protein expressed on the surface of activated T cells. PD-1 is part of the immune system’s normal braking mechanism: it exists to prevent T cells from overreacting and damaging healthy tissue during chronic inflammation.

Tumors exploit this mechanism. Many cancers express PD-L1 (the ligand for PD-1) on their surface or on surrounding immune cells. When a T cell that has recognized a tumor cell attempts to destroy it, the tumor cell’s PD-L1 binds to the T cell’s PD-1, essentially telling the T cell to stand down. The immune response is dampened. The tumor survives.

Pembrolizumab blocks PD-1 from binding to PD-L1 or PD-L2. With the brake released, T cells can recognize and kill tumor cells more effectively. The clinical requirement for this mechanism to work is that the immune system has already mounted some T cell response to the tumor, which is why PD-L1 expression testing is clinically important: tumors with higher PD-L1 expression, measured by the combined positive score (CPS) on immune cells and tumor cells together, are more likely to be in an immunologically active microenvironment where checkpoint blockade can make a meaningful difference.

In TNBC specifically, approximately 40 to 50% of metastatic tumors express PD-L1 at a CPS of 10 or above. This population responds to checkpoint inhibition. The other half, patients with PD-L1-negative or lower-expressing TNBC, generally do not benefit from pembrolizumab-based regimens, which is why the two new TNBC first-line approvals (Trodelvy monotherapy for PD-(L)1-ineligible patients, and Trodelvy plus pembrolizumab for PD-L1-positive patients) are structured around PD-L1 status as a dividing line.

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What Keytruda Qlex Is: The Subcutaneous Formulation Explained

Keytruda Qlex is not a new drug. It contains the same pembrolizumab molecule as IV Keytruda. What is different is how it gets into the body and how long that process takes.

Keytruda Qlex (pembrolizumab and berahyaluronidase alfa-pmph) was first approved by the FDA on September 19, 2025, for adult and pediatric patients (aged 12 and older) across most solid tumor indications already approved for IV pembrolizumab. The June 25, 2026 TNBC approval extends that coverage to this new combination indication.

The co-formulation partner is berahyaluronidase alfa, a variant of human hyaluronidase developed by Alteogen Inc. and licensed to Merck. Hyaluronidase is an enzyme that temporarily breaks down hyaluronan, the polysaccharide that forms the structural matrix of subcutaneous tissue. Hyaluronan creates the physical resistance that limits how much volume can be injected subcutaneously and how quickly it disperses. By transiently degrading this matrix, berahyaluronidase alfa allows a large volume of pembrolizumab to be injected under the skin and absorbed into the systemic circulation, achieving comparable drug exposure to the intravenous formulation.

This approach is not unique to pembrolizumab. The same enzyme-facilitated subcutaneous delivery technology was used previously to create subcutaneous formulations of trastuzumab (Herceptin SC), rituximab (Rituxan Hycela), and daratumumab (Darzalex Faspro). Each followed a similar path: an established IV biologic that patients receive on a recurring schedule, converted to a subcutaneous option to reduce infusion chair time, free up infusion center capacity, and potentially allow administration in broader healthcare settings.

The pharmacokinetic data that supported the approval

The FDA’s September 2025 approval of Keytruda Qlex was based on Study MK-3475A-D77 (NCT05722015), a Phase 3 trial in 377 patients with treatment-naive metastatic NSCLC, randomized 2:1 to subcutaneous Keytruda Qlex every 6 weeks plus platinum doublet chemotherapy or IV pembrolizumab every 6 weeks plus chemotherapy. The primary endpoints were pharmacokinetic: pembrolizumab AUC from 0 to 6 weeks in cycle 1, and trough concentration at steady state in cycle 3. Both met non-inferiority criteria against IV pembrolizumab.

Efficacy outcomes were consistent between formulations: confirmed ORR 45% (Keytruda Qlex) versus 42% (IV pembrolizumab); median PFS 8.1 months versus 7.8 months; no notable OS differences. The conclusion the FDA drew was that the subcutaneous and intravenous formulations are clinically interchangeable across approved indications.

What the administration difference means in practice

Feature	Keytruda (IV pembrolizumab)	Keytruda Qlex (SC pembrolizumab plus berahyaluronidase)
Route	Intravenous infusion	Subcutaneous injection into thigh or abdomen
Administration time	30 minutes per infusion	1 to 2 minutes per injection
Setting	Infusion center (IV access required)	Any clinical setting with a healthcare provider
Every 3 weeks dose	200 mg IV	395 mg pembrolizumab plus 4,800 units berahyaluronidase (2.4 mL)
Every 6 weeks dose	400 mg IV	790 mg pembrolizumab plus 9,600 units berahyaluronidase (4.8 mL)
Additional contraindication	None beyond pembrolizumab standard	Hypersensitivity to berahyaluronidase alfa, hyaluronidase, or excipients

For a patient receiving first-line pembrolizumab plus sacituzumab govitecan for metastatic TNBC, the infusion schedule already involves regular clinic visits for the ADC component of the regimen, which requires IV administration. But over the course of treatment, every component that can be converted from a 30-minute IV session to a 1-minute subcutaneous injection is time and infusion center resources recovered. For patients who respond well and remain on pembrolizumab for extended maintenance, this difference accumulates.

There is also a site-of-care dimension. IV infusions require a healthcare setting with IV access capability and monitoring capacity. Subcutaneous injections can be administered by a healthcare provider in a wider range of settings, including a physician’s office, a community-based clinic, or potentially a home health visit. This flexibility matters for patients in rural areas, patients with transportation barriers, and patients who are otherwise functional but find regular infusion center visits logistically difficult.

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The ASCENT-04 Trial Data: What This Regimen Actually Showed

The clinical evidence supporting this approval is the same Phase 3 ASCENT-04/KEYNOTE-D19 trial covered in detail in our companion Trodelvy post. The key numbers are included here for completeness.

ASCENT-04/KEYNOTE-D19 (NCT05382286) enrolled 443 adults with first-line unresectable locally advanced or metastatic TNBC with PD-L1 CPS at or above 10, confirmed centrally by the PD-L1 IHC 22C3 pharmDx assay. Patients were randomized to sacituzumab govitecan plus pembrolizumab or sacituzumab govitecan plus physician’s choice chemotherapy plus pembrolizumab.

Endpoint	SG plus pembrolizumab	Chemo plus pembrolizumab	Result
Median PFS (BICR)	11.2 months (95% CI 9.3 to 16.7)	7.8 months (95% CI 7.3 to 9.3)	HR 0.65 (95% CI 0.51 to 0.84); p=0.0009
Confirmed ORR	61%	55%	Favors SG plus pembrolizumab
12-month PFS rate	48%	38%	—
Median OS	Not reached	Not reached	Immature; no OS detriment

Source: Tolaney SM et al. NEJM. 2025. doi:10.1056/NEJMoa2511736.

The prior standard of care for PD-L1-positive first-line TNBC was chemotherapy plus pembrolizumab, established by KEYNOTE-522. The ASCENT-04 question was whether replacing chemotherapy with sacituzumab govitecan, a targeted ADC, would improve on that baseline. A 35% reduction in progression risk and a 3.4-month improvement in median PFS over a regimen that already included pembrolizumab answers that question clearly.

The 43% crossover rate in the control arm (chemotherapy plus pembrolizumab patients who received sacituzumab govitecan in the second line) is relevant context for interpreting the OS data when it matures. This level of crossover typically compresses OS differences between arms even when the experimental treatment provides genuine survival benefit.

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The NCCN Category 1 Designation: What It Means for Clinical Practice

The National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Oncology are the most widely followed treatment guidelines in American oncology. Category 1 designation indicates that the recommendation is based on high-level evidence with uniform NCCN consensus that the intervention is appropriate. It is the highest category in the NCCN framework.

Pembrolizumab in combination with sacituzumab govitecan is now a Category 1 preferred first-line treatment option for certain patients with recurrent unresectable or stage IV TNBC whose tumors express PD-L1 at CPS at or above 10, according to the NCCN Clinical Practice Guidelines in Oncology for Breast Cancer. Merck

Category 1 preferred status in NCCN guidelines is clinically significant for several reasons beyond academic endorsement. Many payers use NCCN guidelines to guide formulary and coverage decisions. A Category 1 preferred designation supports prior authorization approvals and reduces the administrative burden on oncology practices seeking to prescribe this regimen for eligible patients. For oncologists managing patients with first-line PD-L1-positive metastatic TNBC, this designation signals that the combination has been independently reviewed and endorsed at the highest evidence tier.

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Pembrolizumab’s Safety Profile: What Has Not Changed

The immune checkpoint inhibitor safety framework for pembrolizumab is well-established across a decade of use. The June 25 approval does not introduce new safety signals for the pembrolizumab component. What follows is a summary of the key risks that patients starting pembrolizumab plus sacituzumab govitecan should understand.

Immune-mediated adverse reactions: This is the defining safety concern of PD-1 inhibition and the source of most serious adverse events. When the PD-1 brake is released, the immune system can attack normal tissues as well as tumor cells. Immune-mediated adverse reactions can affect virtually any organ system and can be severe or fatal. The most clinically important include:

Pneumonitis (immune-mediated lung inflammation): can present as new or worsening shortness of breath, cough, or chest pain. Any new pulmonary symptoms in a patient on pembrolizumab require prompt evaluation. Mild cases may resolve with corticosteroids; severe cases require permanent discontinuation.

Colitis: immune-mediated diarrhea or colitis, ranging from mild loose stools to severe watery or bloody diarrhea. Patients should report significant changes in bowel habits promptly.

Hepatitis: immune-mediated liver inflammation, typically detected on routine liver function testing before clinically apparent. Baseline and periodic LFT monitoring is standard.

Endocrinopathies: thyroid dysfunction (both hypothyroidism and hyperthyroidism), type 1 diabetes, adrenal insufficiency, and hypophysitis (pituitary inflammation) can all occur. Many are manageable with hormone replacement, but adrenal insufficiency and hypophysitis can be life-threatening if unrecognized.

Nephritis: immune-mediated kidney injury, typically detected by rising creatinine.

Skin reactions: rash, dermatitis, bullous pemphigoid, and toxic epidermal necrolysis have been reported.

The general management principle for immune-mediated adverse reactions: mild reactions may be managed with dose holds and monitoring; moderate reactions typically require corticosteroids; severe reactions require high-dose corticosteroids and permanent pembrolizumab discontinuation. Patients and their caregivers should be educated about these symptoms before starting treatment and should contact their oncology team promptly if new symptoms develop.

Keytruda Qlex-specific considerations:

Keytruda Qlex carries an additional contraindication not present for IV Keytruda: patients with known hypersensitivity to berahyaluronidase alfa, hyaluronidase, or any excipients in the formulation should not receive Keytruda Qlex and should receive IV pembrolizumab instead. Local injection site reactions (redness, pain, swelling, bruising at the injection site in the thigh or abdomen) are possible and are not observed with IV administration.

Sacituzumab govitecan toxicities in the combination:

Patients receiving this regimen must also be counseled about the Trodelvy-specific toxicities covered in detail in our companion post: severe neutropenia (boxed warning, grade 3 or higher in approximately 43% in the monotherapy trial; G-CSF prophylaxis strongly recommended), severe diarrhea (boxed warning), and the UGT1A1 pharmacogenomic consideration for patients who are homozygous for the UGT1A1*28 allele and require dose reduction.

Embryo-fetal toxicity: Both pembrolizumab and sacituzumab govitecan can cause fetal harm. Females of reproductive potential should use effective contraception during treatment and for 6 months after the last sacituzumab govitecan dose, and for 4 months after the last pembrolizumab dose.

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PD-L1 Testing: A Required Step Before Starting Treatment

Because this indication is restricted to patients with PD-L1 CPS at or above 10, PD-L1 testing is a prerequisite for prescribing this regimen. The FDA-authorized assay for this indication is the PD-L1 IHC 22C3 pharmDx assay (Agilent/Dako). This companion diagnostic measures PD-L1 expression on both tumor cells and tumor-infiltrating immune cells, combining both into a single combined positive score. CPS at or above 10 is required for eligibility.

For oncology practices newly managing metastatic TNBC patients: PD-L1 testing should be ordered at the time of metastatic diagnosis or at the time of considering first-line treatment, ideally from the most recently obtained tissue sample. The test should specifically report the CPS using the 22C3 antibody clone; other PD-L1 assays (SP142, 28-8) are not validated for this specific indication and should not be substituted.

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Practical Administration: Choosing Between IV Keytruda and Keytruda Qlex

For patients who are starting this combination regimen and whose oncology team has access to Keytruda Qlex, the choice between IV pembrolizumab and subcutaneous Keytruda Qlex is a shared clinical and patient preference decision. The efficacy is equivalent. The safety profiles are essentially the same, with the addition of the hyaluronidase hypersensitivity contraindication for Keytruda Qlex.

The subcutaneous option makes the most practical sense for patients who place high value on reducing infusion center time, who have poor venous access making IV cannulation difficult or painful, who live far from infusion centers and could benefit from a broader range of administration sites, or who are responding well to treatment and anticipate long-term maintenance.

The IV option remains appropriate and equivalent for patients in infusion center settings where the 30-minute administration time is not a barrier, for patients with known hypersensitivity to hyaluronidase components, and for pediatric patients under 12 years of age for whom Keytruda Qlex is not currently approved.

For related HED coverage on this treatment approach from the sacituzumab govitecan angle, see our companion post on Trodelvy (sacituzumab govitecan-hziy) receiving two new first-line TNBC approvals on June 24, 2026, which covers the ADC mechanism, the ASCENT-03 monotherapy trial for PD-(L)1-ineligible patients, and the full ASCENT-04 efficacy data in depth. For broader context on checkpoint inhibitor safety and patient education, see our coverage of the FDA’s accelerated approval of Tzield (teplizumab) as the first disease-modifying therapy for recently diagnosed Stage 3 type 1 diabetes, which covers immune-related adverse event monitoring principles relevant across checkpoint inhibitor therapy.

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Sources

Merck FDA approval press release (June 25, 2026): FDA Approves KEYTRUDA and KEYTRUDA QLEX, each with Trodelvy, as First-Line Treatment of PD-L1+ Advanced TNBC. Merck. BusinessWire. June 25, 2026.

Merck.com detailed announcement: FDA Approves KEYTRUDA and KEYTRUDA QLEX each with Trodelvy for First-Line TNBC. merck.com. June 25, 2026.

Drugs.com approval news: FDA Approves Keytruda and Keytruda Qlex each with Trodelvy as First-Line Treatment of PD-L1+ Advanced TNBC. drugs.com. June 25, 2026.

FDA original Keytruda Qlex approval (September 19, 2025): FDA approves pembrolizumab and berahyaluronidase alfa-pmph for subcutaneous injection. FDA.gov. September 19, 2025.

Merck Keytruda Qlex original approval press release: FDA Approves Merck’s KEYTRUDA QLEX for Subcutaneous Use in Adults Across Most Solid Tumor Indications. merck.com. September 19, 2025.

Cancer Therapy Advisor (Keytruda Qlex mechanism and approval): Keytruda Qlex, an SC Formulation of Pembrolizumab, Gets FDA Approval. cancertherapyadvisor.com. September 2025.

Pharmacy Times (Keytruda Qlex clinical review): The FDA Approval of Keytruda Qlex: A Subcutaneous Version of Pembrolizumab. pharmacytimes.com.

Keytruda Qlex approval history: Keytruda Qlex FDA Approval History. drugs.com.

Study MK-3475A-D77 (Keytruda Qlex PK trial): NCT05722015. ClinicalTrials.gov.

ASCENT-04/KEYNOTE-D19 primary NEJM publication: Tolaney SM et al. Sacituzumab govitecan plus pembrolizumab in first-line PD-L1-positive TNBC. NEJM. 2025. doi:10.1056/NEJMoa2511736.

ASCENT-04 trial registration: NCT05382286. ClinicalTrials.gov.

Keytruda Qlex prescribing information (HCP site): KEYTRUDA QLEX Prescribing Information and HCP site. keytrudahcp.com.

Keytruda Qlex patient site: KEYTRUDA QLEX for patients. keytruda.com.

Medscape (Keytruda Qlex drug reference): Keytruda Qlex (pembrolizumab/berahyaluronidase) drug reference. Medscape.

Pembrolizumab mechanism and PD-1 biology: Pembrolizumab. StatPearls. NCBI.

PD-1/PD-L1 immune checkpoint review: PD-1/PD-L1 Pathway. PMC4868169.

NCCN Breast Cancer Guidelines: NCCN Clinical Practice Guidelines in Oncology: Breast Cancer. nccn.org.

PD-L1 22C3 pharmDx companion diagnostic: List of Cleared or Approved Companion Diagnostic Devices. FDA.gov.

Keytruda approval history (over 20 indications): Keytruda FDA Approval History. drugs.com.

Patient resources: National Breast Cancer Foundation | Susan G. Komen Foundation | TOUCH, The Black Breast Cancer Alliance | Merck patient access program for Keytruda | Merck Access Bridge

Disclaimer: Health Evidence Digest provides general information about FDA approvals and health research for educational purposes. This content is not a substitute for professional medical advice. Keytruda (pembrolizumab) and Keytruda Qlex carry serious risks including immune-mediated adverse reactions that can be severe or fatal and can affect any organ system. PD-L1 testing to confirm CPS at or above 10 is required before initiating this regimen. All treatment decisions for metastatic TNBC should be made in close collaboration with a board-certified medical oncologist experienced in breast cancer and immunotherapy management.

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