A Study to Find Out Whether BI 1015550 Improves Lung Function in People With Progressive Fibrosing Interstitial Lung Diseases (PF-ILDs)

Inclusion criteria

1. Patients ≥18 years old at the time of signed informed consent.

2. Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to admission to the trial.

3. Diagnosis of progressive fibrosing ILD other than IPF (physician confirmed).

4. Patients may be either:

• on a stable therapy* with nintedanib for at least 12 weeks prior to Visit 1 and during screening and are planning to stay on this background treatment after randomization. (*stable therapy is defined as a tolerated regimen of nintedanib (with no dose changes) for at least 12 weeks)

• not on treatment with nintedanib for at least 8 weeks prior to Visit 1 and during the screening period (e.g. either Antifibrotic (AF)-treatment naïve or previously discontinued) and do not plan to start or re-start antifibrotic treatment.

5. Forced Vital Capacity (FVC) ≥45% of predicted normal at Visit 1.

6. DLCO ≥25% of predicted normal corrected for hemoglobin (Hb) at Visit 1.

7. Women of childbearing potential (WOCBP) must be ready and able to use highly effective methods of birth control. WOCBP taking oral contraceptives (OCs) also have to use one barrier method

8. Patients treated with permitted immunosuppressive agents (other than corticosteroids) for an underlying systemic disease (e.g. Methotrexate (MTX), Azathioprine (AZA)) need to be on a stable treatment for at least 12 weeks prior to Visit 1 and during the screening period.

Exclusion criteria

1. Prebronchodilator Forced Expiratory Volume in 1 second (FEV1)/Forced vital capacity (FVC) <0.7 at Visit 1

2. In the opinion of the Investigator, other clinically significant pulmonary abnormalities.

3. Acute Interstitial Lung Disease (ILD) exacerbation within 3 months prior to Visit 1 and/or during the screening period (investigator-determined).

4. Relevant chronic or acute infections including human immunodeficiency virus (HIV) and viral hepatitis.

5. Patients having developed ILD due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection/coronavirus disease 2019 (COVID-19) within 12 months of screening (based on investigators judgement).

6. Major surgery (major according to the investigator's assessment) performed within 6 weeks prior to Visit 2 or planned during the trial period, e.g. hip replacement. Registration on lung transplantation list would not be considered as planned major surgery.

7. Any documented active or suspected malignancy or history of malignancy within 5 years prior to Visit 1, except appropriately treated basal cell carcinoma of the skin, in situ squamous cell carcinoma of the skin or in situ carcinoma of uterine cervix.

8. Aspartate aminotransferase (AST) or Alanine Aminotransferase (ALT) >2.5 x upper limit of normal (ULN) or total Bilirubin >1.5 x ULN at Visit 1.

Further exclusion criteria apply.