Roche Wins FDA Approval for Enspryng Despite Mixed Phase III Results

The U.S. Food and Drug Administration (FDA) has approved Roche’s Enspryng (satralizumab-mwge) for adults with thyroid eye disease (TED), introducing the first and only at-home subcutaneous treatment option for the condition. Following healthcare-provider training, patients or caregivers can administer the treatment at home, with maintenance dosing every four weeks.

TED, also known as Graves’ ophthalmopathy, is an autoimmune inflammatory disease affecting tissues around the eyes. Symptoms include eyelid retraction, redness, swelling, proptosis (eye bulging), diplopia (double vision) and pain. Severe disease can threaten vision and affect quality of life. Roche estimates that TED affects approximately 155 people per 100,000 in the United States.

The approval follows priority review and expands Enspryng’s use beyond neuromyelitis optica spectrum disorder (NMOSD), for which it was first approved in 2020.

SatraGO-2 Demonstrated Significant Improvements in Eye Bulging and Double Vision

The approval was supported by two Phase III studies, SatraGO-1 (NCT05987423) and SatraGO-2 (NCT06106828). The identically designed, randomized, placebo-controlled trials enrolled 258 participants across 19 countries. They evaluated adults with active, moderate-to-severe TED and inactive TED. The primary endpoint assessed the proportion of participants with active TED achieving at least a 2 mm reduction in proptosis in the study eye at Week 24.

The trials produced different statistical outcomes for this primary endpoint. In SatraGO-1, 49.0% of patients receiving satralizumab achieved a proptosis response, compared with 31.2% receiving placebo. Although the result favoured treatment numerically, it did not reach statistical significance (P=0.0715).

In SatraGO-2, the corresponding response rates were 52.9% with satralizumab and 23.4% with placebo, a statistically significant difference (P=0.0011). The findings indicate a numerical treatment advantage across both studies, but the primary endpoint was met in only one trial.

Diplopia outcomes followed a similar pattern. In SatraGO-1, a reduction in diplopia was reported in 44.4% of patients receiving satralizumab versus 34.4% receiving placebo; this difference was not statistically significant (P=0.3371). In SatraGO-2, the respective rates were 60.7% and 25.8%, with a statistically significant difference (P=0.0044).

The published results also reported improvements in Clinical Activity Score (CAS), a measure of inflammatory disease activity. In both trials, a reduction of at least two CAS points was more frequent with satralizumab than with placebo. These findings add evidence of an anti-inflammatory effect, although not all efficacy comparisons across the programme reached statistical significance.

IL-6 Receptor Inhibition Provides the Mechanistic Rationale

Satralizumab is a humanized monoclonal antibody that binds soluble and membrane-bound interleukin-6 receptors (IL-6R), inhibiting IL-6-mediated signalling. The treatment also uses Chugai’s antibody-recycling technology, designed to support repeated target engagement and sustained inhibition of IL-6 signalling.

The mechanism provides a rationale for targeting inflammation in TED, but the clinical results, rather than the mechanism alone, determine the strength of the efficacy evidence.

Through Week 24, the trials identified no new safety signals. Published findings described satralizumab as generally well tolerated, with low rates of serious adverse events, treatment discontinuations and infections, and no serious infections reported in the satralizumab groups. The safety profile was consistent with the drug’s established experience in NMOSD. Longer-term follow-up remains relevant to understanding the treatment’s durability and safety in TED.

Clinical Interpretation

Enspryng’s approval adds an at-home subcutaneous option for adults with TED, potentially reducing the practical burden associated with treatment administration. SatraGO-2 demonstrated statistically significant improvements in proptosis and diplopia, outcomes directly relevant to patients’ visual function and disease burden.

However, SatraGO-1 did not meet its prespecified primary endpoint, despite a numerical advantage for satralizumab. The difference between the trials warrants careful interpretation and prevents treating the primary-endpoint evidence as uniformly positive across the Phase III programme.

The published analysis also reported benefits in the combined active and inactive TED population, but the inactive subgroup was relatively small and the investigators cautioned that firm conclusions could not be drawn for this group alone. Further follow-up will help clarify the durability of benefit and the treatment’s role across different TED populations.

The approval establishes a new treatment option, while the totality of evidence should be interpreted with attention to differences between trials, endpoint-specific results and the remaining uncertainty around individual patient response.

References

Genentech/Roche. FDA approves Enspryng as the first and only at-home subcutaneous treatment option for thyroid eye disease. October 2026.

Study to Evaluate the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Satralizumab in Participants with Thyroid Eye Disease (SatraGO-1), ClinicalTrials.gov ID NCT05987423

A Study to Evaluate the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Satralizumab in Participants with Thyroid Eye Disease (SatraGO-2), ClinicalTrials.gov ID NCT06106828