A Phase II Randomised, Double-blinded, Placebo-controlled Study to Evaluate the Efficacy, Safety, and Tolerability of Four Orally Administrated Doses of BI 409306 During a 12-week Treatment Period in Patients With Schizophrenia on Stable Antipsychotic Treatment

Suicidality as Assessed by Columbia Suicidal Severity Rating Scale (C-SSRS)

Time Frame: Up to 12 weeks

C-SSRS: Number (%) of subjects with an event of Suicidal Ideation (Wish to be dead, Non-specific active suicidal thoughts, Active suicidal ideation with any methods (not plan) without intent to act, Active suicidal ideation with some intent to act without specific plan, Active suicidal ideation with specific plan and intent) or Suicidal Behavior (Preparatory acts or behavior, Aborted attempt, Interrupted attempt, Non-fatal suicide attempt, Completed suicide) or Self-injurious behavior without suicidal intent is presented. C-SSRS used only to evaluate whether the patient developed suicidal ideation or behavior and no composite score will be used. Questions in the 1st section of suicidal ideation and suicidal behavior assessments in C-SSRS are "yes" and "no" type questions. If patient had suicidal ideation or behavior, 2nd section will be performed to evaluate the details with the scale from 0 to 5 or 0 to 2 and the larger number means the more severe condition.

Occurrence of Serious Adverse Events (SAEs) (Including the Abnormalities of Physical Examination, Vital Signs, Electrocardiogram (ECG) Test and Laboratory Tests)

Time Frame: Up to 20 weeks

Occurrence of serious adverse events (SAEs) (including the abnormalities of physical examination, vital signs, electrocardiogram (ECG) test and laboratory tests).

Dramatic Worsening of Disease State as Assessed by Positive and Negative Syndrome Scale (PANSS)

Time Frame: Baseline, Week 6 and Week 12

Dramatic worsening of disease state as assessed by Positive and Negative Syndrome Scale (PANSS). It contains 30-items including seven positive symptom items, seven negative symptom items and 16 general psychopathology symptom items. Each item was scored on the same seven point severity scale. Fourteen of the PANSS items required input from an informant. Total score ranges from 30 to 210 (minimum is better). The descriptive statistics of change from baseline (CFB) in PANSS score at week 6 (W6) and week 12 (W12) are presented.

Occurrence of Protocol-specified Adverse Events of Special Interest (AESI)

Time Frame: Up to 20 weeks

Occurrence of Protocol-specified adverse events of special interest (AESI).

Change From Baseline in the Composite Score of Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) Consensus Cognitive Battery (MCCB) After 12 Weeks of Treatment

Time Frame: Baseline and Week 12

MCCB comprises 10 tests, which assess 7 cognitive domains, including speed of processing, attention vigilance, working memory, verbal learning, visual learning, reasoning problem solving, and social cognition. The composite score was calculated by summing over the standardised score of each domain for analysis and it varies from -20 to 99 with higher score indicating better outcome. The trial was set up as "learn and confirm" model including 2 stages. Stage 1 analysis was conducted to identify the meaningful cognition endpoint(s) (CANTAB domain(s)) and the selected endpoint(s) were to be pre-specified as the primary endpoint(s) for Stage 2 analysis. Since none of the CANTAB outcome measures was selected in the Stage 1 analysis at planned time based on the pre-specified criteria, the MCCB composite score was chosen as the primary endpoint in the Stage 2 analysis, as pre-defined.