Investigational Drug
fianlimab
TrialFetch AI Analysis
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Overview
Fianlimab (REGN3767) is an investigational, fully human, hinge-stabilized IgG4 monoclonal antibody targeting lymphocyte activation gene-3 (LAG-3). It is being developed primarily with the anti–PD-1 antibody cemiplimab. As of September 22, 2026, fianlimab remains unapproved, and its strongest clinical evidence is in advanced melanoma. (aacrjournals.org)
Mechanism of action
LAG-3 is an inhibitory immune-checkpoint receptor expressed on activated T cells. Fianlimab binds LAG-3 and blocks its interaction with MHC class II, thereby reducing inhibitory signaling and restoring T-cell activation. Preclinical models showed greater antitumor activity when LAG-3 blockade was combined with cemiplimab-mediated PD-1 blockade. Its Fc region was engineered to minimize antibody-dependent cytotoxicity against LAG-3-expressing immune cells. (aacrjournals.org)
Efficacy
In a published phase 1 study, 98 patients with advanced melanoma who had not received anti–PD-1 therapy for advanced disease had an investigator-assessed objective response rate (ORR) of 61.2% with fianlimab plus cemiplimab and a median progression-free survival (PFS) of 13.3 months after 12.6 months’ median follow-up. ORRs were 63% in anti–PD-1-naïve patients, 63% in systemic-treatment-naïve patients, and 56% in patients previously treated in the neoadjuvant or adjuvant setting. Among 15 patients previously treated with anti–PD-1 therapy for advanced disease, ORR was 13.3% and median PFS was 1.5 months. (pubmed.ncbi.nlm.nih.gov)
Longer follow-up of the 98-patient population, reported in a 2026 conference proceeding, found a blinded-independent-review ORR of 57%, including a 25% complete-response rate; median PFS was 24 months, while median overall survival had not been reached. These single-arm findings require interpretation alongside randomized evidence. (scholarlycommons.henryford.com)
In a 1,546-patient randomized phase 3 trial in previously untreated unresectable or metastatic melanoma, neither tested dose of fianlimab plus cemiplimab significantly improved PFS over pembrolizumab. Median PFS was 11.5 months with high-dose fianlimab, 9.6 months with low-dose fianlimab, and 6.4 months with pembrolizumab. For the high-dose comparison, the hazard ratio was 0.845 (95% CI 0.709–1.008; p=0.0627). These results were disclosed by the manufacturer in May 2026 and had not yet been presented as a peer-reviewed publication in the sources reviewed. (investor.regeneron.com)
Safety
In the published melanoma phase 1 study, grade 3 or higher treatment-emergent adverse events occurred in 44% of anti–PD-1-naïve patients, while grade 3 or higher treatment-related events occurred in 22%. Common events included fatigue, nausea, diarrhea, rash and pruritus. Adrenal insufficiency occurred in 12% overall and was grade 3–4 in 4%, a higher incidence than generally reported with PD-1 monotherapy. Treatment-related adverse events caused discontinuation in 13%; two treatment-related deaths were reported. (pmc.ncbi.nlm.nih.gov)
The phase 3 announcement stated that no new safety signals were identified, but detailed safety results were not provided. (investor.regeneron.com)
Further reading
- Phase 1 study in advanced melanoma — Journal of Clinical Oncology/PubMed
- Full text of the phase 1 melanoma study
- Preclinical characterization — Molecular Cancer Therapeutics
- 2026 longer-follow-up conference proceeding
- May 2026 phase 3 results announcement
Last updated: Sep 2026
Active trials using fianlimab
Found 8 active trials using this drug:
TrialFetch AI summary: Adults with PD-L1–positive (CPS ≥1), incurable recurrent or metastatic HNSCC who have not received systemic therapy for recurrent or metastatic disease are randomized within HPV-positive and HPV-negative cohorts. Treatment is investigational fianlimab (anti–LAG-3) plus cemiplimab (anti–PD-1) versus cemiplimab plus placebo.
ClinicalTrials.gov ID: NCT06769698
TrialFetch AI summary: Adults with clear cell renal cell carcinoma and 1–5 metastatic lesions amenable to stereotactic body radiotherapy (SBRT) receive SBRT to active sites, then are randomized to cemiplimab (anti–PD-1) alone or with investigational fianlimab (anti–LAG-3) every 3 weeks for up to 1 year.
ClinicalTrials.gov ID: NCT07223541
TrialFetch AI summary: Adults with previously untreated, unresectable locally advanced or metastatic clear-cell RCC across all IMDC risk groups are randomized to fianlimab (investigational anti-LAG-3 antibody) plus cemiplimab (anti-PD-1), with or without ipilimumab (anti-CTLA-4), or standard ipilimumab plus nivolumab (anti-PD-1).
ClinicalTrials.gov ID: NCT07188896
TrialFetch AI summary: For patients with measurable, progressive platinum-resistant serous or endometrioid ovarian, primary peritoneal, or fallopian tube cancer and ECOG performance status 0–1, this study evaluates ubamatamab, an investigational MUC16×CD3 T-cell–engaging bispecific antibody, with sarilumab. Other arms add bevacizumab, pegylated liposomal doxorubicin, or cemiplimab plus investigational fianlimab, an anti–LAG-3 antibody.
ClinicalTrials.gov ID: NCT06787612
TrialFetch AI summary: Adults with unresectable or metastatic cutaneous or mucosal melanoma progressing after PD-1 monotherapy or PD-1/LAG-3 blockade receive fianlimab (investigational anti–LAG-3), cemiplimab (anti–PD-1), and ipilimumab (anti–CTLA-4). Patients must have ECOG 0–1; untreated CNS metastases and uveal melanoma are excluded.
ClinicalTrials.gov ID: NCT06594991
TrialFetch AI summary: For patients with previously untreated unresectable stage III or metastatic melanoma and ECOG performance status 0–1, this trial compares fixed-dose fianlimab plus cemiplimab with relatlimab plus nivolumab. Fianlimab is an investigational anti–LAG-3 antibody; cemiplimab blocks PD-1.
ClinicalTrials.gov ID: NCT06246916
TrialFetch AI summary: Adults with locally advanced head and neck basal cell carcinoma that is unresectable or would require highly morbid surgery receive neoadjuvant cemiplimab (anti–PD-1) alone or with investigational fianlimab (anti–LAG-3) before surgery. Prior immunotherapy or hedgehog inhibitor treatment for malignancy is excluded.
ClinicalTrials.gov ID: NCT05929664
TrialFetch AI summary: Eligible patients have previously platinum-treated advanced epithelial ovarian, fallopian tube, or primary peritoneal cancer, or recurrent/progressive endometrial cancer after platinum chemotherapy and anti–PD-1 therapy; ECOG performance status must be 0–1. Treatment is REGN5668, an investigational MUC16×CD28 bispecific antibody that provides tumor-directed T-cell costimulation, alone or with cemiplimab (anti–PD-1), cemiplimab plus fianlimab (anti–LAG-3), or ubamatamab (MUC16×CD3), with or without sarilumab.
ClinicalTrials.gov ID: NCT04590326
