The aim of this study is to describe the forced expiratory volume in 1 second (FEV1) decline and natural disease evolution in patients affected by CLAD-BOS after lung transplantation and receiving an immunosuppressive therapy as standard of care.

This is a retrospective, multinational, multicenter chart review study of adult patients with clinically diagnosed CLAD-BOS after lung transplantation. All data will be retrospectively collected from patient records starting from lung transplantation date through last date of available data, and as such, no interventions will be applied as part of this study.

The observational period for each patient will be from lung transplant date until last date of data available or death, whichever occurs earlier and will include the following time periods:

Diagnosis window: 01 January 2013 through most recent data available.

Inclusion Criteria:

1. Adult patients ≥ 18 years of age on the date of CLAD-BOS diagnosis
2. Patients with a CLAD-BOS clinician diagnosis from as early as 01 January 2013
3. Patients with CLAD-BOS clinician diagnosis made at least 12 months after lung transplant
4. Patients received at least basic maintenance regimen of immunosuppressive agents including tacrolimus, a second agent such as but not limited to mycophenolate mofetil or azathioprine (or other anti-proliferative agent), and a systemic corticosteroid such as prednisone as third agent for at least 1 month before the index date. As long as the basic maintenance regimen is maintained for the abovementioned period, patients will still be considered eligible for the study even if they are receiving other immunosuppressive agents in addition to the basic maintenance regimen.

Exclusion Criteria:

1. Patients with severe concomitant disease at the time of index date, which according to physician's judgment, can interfere with CLAD-BOS progression and mortality (e.g., malignancies, severe chronic diseases)
2. Patients who have been exposed to any investigational medical products in the 4 weeks prior to index date or during the post-diagnosis period
3. Patients with confirmed other CLAD phenotype (e.g., restrictive allograft syndrome) according to physician's judgment.

The study population will include adult patients aged ≥ 18 years who are recipients of a lung transplant and diagnosed with CLAD-BOS from the first of January 2013 following transplantation.