Secukinumab missed its mark in a giant cell arteritis trial

Secukinumab, a monoclonal antibody that blocks the inflammatory signal interleukin-17A, did not significantly outperform placebo for keeping giant cell arteritis in remission over a year in the phase 3 GCAptAIN trial [s1]. The result matters because it closes off a hoped-for second targeted option for a disease in which the only proven alternative to prolonged steroids is the interleukin-6 blocker tocilizumab [s1][s2].

Giant cell arteritis is the most common inflammatory disease of large arteries in older adults. It is treated urgently with high-dose glucocorticoids to prevent complications such as sudden vision loss, but the disease frequently relapses when steroids are tapered, and the months or years of glucocorticoid exposure carry their own toll — infection, bone loss, diabetes and more [s2]. The central problem in managing the condition is therefore how to control the arteritis while getting patients off steroids faster. Tocilizumab, which interrupts interleukin-6 signalling, was the first drug shown in a randomised trial to do that and is written into treatment guidelines as the steroid-sparing agent of choice [s2][s3]. Interleukin-17A is a different inflammatory pathway implicated in the arterial wall, and secukinumab — already licensed for psoriasis and related conditions — was the leading candidate to test it.

What the trial did

GCAptAIN was a randomised, double-blind, placebo-controlled, multicentre phase 3 trial funded by Novartis, which makes secukinumab [s1]. Patients with new-onset or relapsing giant cell arteritis were first randomly assigned 2:1 to 300 mg of secukinumab (SEC-300) or placebo; after a protocol amendment, assignment moved to 1:1:1 between SEC-300, a 150 mg dose (SEC-150), and placebo [s1]. The design deliberately handicapped the drug against a slower steroid withdrawal: patients on secukinumab followed a 26-week glucocorticoid taper, while the placebo group tapered over the full 52 weeks [s1]. In all, 140 patients were analysed in the SEC-300 group, 98 in the SEC-150 group and 115 on placebo [s1].

The primary outcome was the proportion of patients in sustained remission at week 52, comparing SEC-300 with placebo [s1]. That endpoint mirrors the design of the earlier tocilizumab trial, GiACTA, which randomised 251 patients to weekly or fortnightly tocilizumab plus a 26-week prednisone taper against placebo plus a 26- or 52-week taper, with sustained glucocorticoid-free remission at week 52 as its primary measure [s2].

What it found

Sustained remission at week 52 occurred in 25.6% of the SEC-300 group versus 16.9% of the placebo group — a difference of 8.7 percentage points whose 95% confidence interval ran from −1.3 to 18.8 (P=0.09) [s1]. Because that interval crossed zero and the P value sat above the conventional threshold, the trial did not demonstrate a statistically significant benefit for its primary comparison [s1]. The lower 150 mg dose fared worse still: 19.4% remission versus 17.7% for the placebo patients enrolled after the amendment, a gap of 1.6 percentage points (95% CI −9.2 to 12.4) [s1].

Safety did not raise new alarms. Adverse events were common across all groups — 92.9% on SEC-300, 95.9% on SEC-150 and 97.4% on placebo — while serious adverse events were, if anything, less frequent on the drug: 20.0% for SEC-300, 27.6% for SEC-150 and 32.2% for placebo, a pattern consistent with the steroid-related harms the trial was trying to reduce [s1]. Serious infections occurred in 5.0%, 9.2% and 6.1% of the three groups respectively [s1].

How to read it

The honest reading is that the numbers pointed in secukinumab's favour but did not clear the bar the trial set for itself. A nominal 8.7-percentage-point advantage is not nothing, and the safety signal was reassuring, but a confidence interval that includes zero means the result is compatible with no real benefit [s1]. The trial's own design also worked against a clean answer: because the placebo group tapered steroids over twice as long, some of the apparent gap could reflect the faster withdrawal forced on the drug arm rather than the drug itself [s1]. Guidelines set the standard for adopting a new steroid-sparing biologic at a demonstrated, not a suggestive, effect [s3].

This is the value of a negative trial. Interleukin-17A blockade was a biologically reasonable idea, and had GCAptAIN not been run, secukinumab might have drifted into off-label use on the strength of its plausibility. The trial instead shows that, on the evidence in hand, it does not join tocilizumab as an established option. For the difference between a cytokine target that clears a remission endpoint and one that does not, related coverage has examined interleukin-6 blockade in thyroid eye disease and what the cardiovascular data on IL-17 inhibitors such as secukinumab in psoriasis actually show.

What to watch

The published analysis is the pivotal week-52 comparison; longer-term and subgroup data may refine whether any particular patients benefit [s1]. More broadly, giant cell arteritis remains a disease with a single proven steroid-sparing drug, so the field's attention turns to other mechanisms in testing and to how tocilizumab is best used — for how long, and in whom — questions the current guideline leaves partly open [s2][s3].

This article describes research and is not medical advice. Treatment of giant cell arteritis, including the use and tapering of glucocorticoids, is a decision for treating clinicians.

Sources

• Secukinumab for Giant Cell Arteritis — NEJM Evidence, 3 June 2026
• Trial of Tocilizumab in Giant-Cell Arteritis — New England Journal of Medicine, 27 July 2017
• 2021 ACR/Vasculitis Foundation Guideline for the Management of Giant Cell Arteritis and Takayasu Arteritis — Arthritis & Rheumatology, 8 July 2021