A Study of Secondary Immunodeficiencies in Adults With Blood Cancers in Kazakhstan Who Have a Weakened Immune System (K-SIDE Study)

Some people with blood cancers (hematologic malignancies) develop a weakened immune system because of their condition or the medicines used to treat it. This is called a secondary immunodeficiency or SID. A weakened immune system can make it harder for the body to fight infections. SIDs make participants more likely to have serious infections, need treatment at a hospital, and need longer treatment periods with antibiotics. SIDs are common but often overlooked in people with blood cancers in Kazakhstan. Currently, Kazakhstan does not have national guidelines for diagnosing and managing SIDs, which leads to differences in how people are assessed and treated across healthcare settings. The main aim of this study is to understand how common SIDs are in adults with blood cancers in Kazakhstan, which people are most affected and how often related health problems such as infections happen. Other aims are to learn more about SIDs in Kazakhstan: how SIDs are treated, how they affect a person's health and daily life (clinical burden) and how certain factors (such as age, health condition, treatment, type and stage of the blood cancer) may influence SIDs. This study will not collect any new data. It will use existing health records and data from Kazakhstan's national oncology registry.

Inclusion Criteria: Participants must meet all of the following criteria: * Adults greater than or equal to (\>=)18 years of age. * Confirmed diagnosis of a hematologic malignancy (preceding SID diagnosis and/or evidence, as defined in inclusion criterion 4), including but not limited to: * Multiple Myeloma * Chronic Lymphocytic Leukemia * Non-Hodgkin Lymphoma * Acute Leukemia * Myeloproliferative Neoplasm * Available EHR data within the study observation period. * For the SID cohort: confirmed diagnosis of SID OR evidence of secondary immunodeficiency, defined by one or more of the following: * Serum IgG \=3 infections per annum requiring treatment with antibiotics (ideally microbiologically proven), and/or * Radiologically proven pneumonia, and/or * Culture-proven sepsis or febrile neutropenia, and/or * Other infection requiring hospitalization and IV antibiotics Exclusion Criteria: Participants meeting any of the following criteria will be excluded: * Age \