Developing a Patient-Reported Outcome (PRO) Screening Measure for Infections and Measuring Quality of Life in Hematological Patients With Secondary Immunodeficiency (SID) Across the Treatment Trajectory - The PRO SID Project

The goal of this observational study is to improve the treatment of hematological patients with secondary immunodeficiency (SID) by developing a patient-reported outcome (PRO) instrument to detect clinically diagnosed infections. The study focuses on adults diagnosed with chronic lymphocytic leukemia (CLL) or multiple myeloma (MM) who are at increased risk of infections due to SID. The main questions it aims to answer are: 1. Can a newly developed PRO screening tool for infection-related symptoms reliably detect infections in patients with SID? 2. How does the health-related quality of life change over the treatment course Participants will: * Complete daily electronic PRO questionnaires (ePRO) to monitor infection-related symptoms * Complete ePRO health-related quality of life questionnaires every 1.5 months * Participate in study visits every three months to ensure documentation of clinical data