The purpose of this study is to evaluate the effect of two different doses of ianalumab versus placebo in addition to first-line corticosteroids in increasing the rate of stable response off treatment at 12 months (SROT-12) in adult participants with primary ITP.

This is a multi-center, randomized, double-blind Phase 3 study to assess the efficacy and safety of two different doses of ianalumab compared to placebo in adults with primary ITP (platelets count <30 G/L) who require first-line standard-of-care corticosteroids.

After completion of the screening period, the participants will enter the randomized treatment period (ianalumab/placebo with standard of care corticosteroids).

After the treatment period, all participants will enter the follow-up period to be monitored for efficacy and safety or safety only depending on how they respond to the study treatment.

The efficacy and safety follow-up period will last until treatment failure or up to 39 months after randomization of the last patient, whichever occurs first. Safety follow-up period will be performed for at least 20 weeks and up to 2 years after the last ianalumab/placebo dose.

The primary endpoint was updated in May 2026 to stable response off treatment at 12 months (SROT-12). The previous primary endpoint, time to treatment failure (TTF), remains in the study as a key secondary objective.

Inclusion Criteria:

• Signed informed consent prior to participation in the study.
• Male or female participants aged 18 years and older on the day of signing informed consent
• Primary ITP diagnosed within 3 months before initiating first-line ITP therapy (corticosteroids, IVIG)
• Platelet count below 30 G/L before starting any first-line ITP therapy (corticosteroids, IVIG)
• Response (platelet count >=50 G/L) to corticosteroids (+/- IVIG) at any time prior to randomization. Note: Platelet count measured within 7 days of platelet transfusion will not be considered as response.

Key Exclusion Criteria:

• Evans syndrome or any other cytopenia (patients with low grade anemia related to bleeding or iron deficiency are eligible)
• Current life-threatening bleeding
• Previous ITP treatment, including splenectomy, except for corticosteroids and/or IVIG initiated as first-line therapy for up to 28 days before randomization and rescue corticosteroids and/or IVIG given prior to confirmed diagnosis of primary ITP .
• Prior use of B-cell depleting therapy (e.g., rituximab).
• Absolute neutrophil count below 1.0 G/L at randomization
• Participants with concurrent coagulation disorders and/or receiving anti-platelet or anticoagulant medication with an exemption of low dose of acetylsalicylic acid

Other protocol-defined Inclusion/Exclusion may apply.

Novartis is committed to sharing with qualified external researchers, access to patient-level data and supporting clinical documents from eligible studies. These requests are reviewed and approved by an independent review panel on the basis of scientific merit. All data provided is anonymized to respect the privacy of patients who have participated in the trial in line with applicable laws and regulations.

This trial data availability is according to the criteria and process described on www.clinicalstudydatarequest.com