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Background Multiple myeloma (MM) is one of the most common hematological neoplasms and accounts for approximately 1% of human cancers. Objectives Description of current diagnostics and classification of MM and related plasma cell neoplasms from the pathology viewpoint. Materials and methods Current knowledge regarding pathology and genetics of MM is summarized and tissue-based diagnostics following international consensus classifications and the current S3 guideline are described. Results MM and related neoplasms are composed of malignant plasma cells that secrete a monoclonal immunoglobulin, which is an important parameter of disease activity. MM shows a multistage development. Almost all cases are preceded by a clinically inapparent precursor lesion, monoclonal gammopathy of undetermined significance (MGUS), which can progress to smoldering myeloma with a higher tumor burden, but absence of organ damage. Systemic MM needs to be discerned from the localized forms, solitary osseous and primary extramedullary plasmacytoma. MM is genetically very heterogeneous and can be broadly subdivided into two cytogenetic groups, cases with primary IGH translocations and cases with hyperdiploidy. Intratumoral genetic heterogeneity is frequently pronounced and correlates with the size of focal lesions in imaging. Conclusions Diagnosis of plasma cell neoplasms is done according to the criteria of the International Myeloma Working Group (IWMG) and requires interdisciplinary evaluation of clinical, serological, pathological and radiological features. In addition to clinical parameters, molecular markers, especially cytogenetic aberrations, are of great prognostic relevance.

The pandemia of coronavirus disease 2019 (COVID-19) has caused more than 355,000 confirmed deaths worldwide. However, publications on postmortem findings are scarce. We present the pulmonary findings in four cases of fatal COVID-19 with a spectrum of lung pathology reflecting disease course and duration, invasive therapies, and laboratory features. Early disease is characterized by neutrophilic, exudative capillaritis with microthrombosis and high levels of IL-1beta and IL-6. Later stages are associated with diffuse alveolar damage and ongoing intravascular thrombosis in small to medium-sized pulmonary vessels, occasionally with areas of infarction equivalents, accompanied by laboratory features of disseminated intravascular coagulation. In late stages, organizing pneumonia with extensive intra-alveolar proliferation of fibroblasts and marked metaplasia of alveolar epithelium can be observed. Viral RNA is encountered in the lung, with virus particles in endothelial cells and pneumocytes. In many patients, multi-organ failure with severe liver damage sets in finally, possibly as consequence of an early-onset pro-inflammatory cytokine storm and/or thrombotic microangiopathy. Electronic supplementary material The online version of this article (10.1007/s00428-020-02881-x) contains supplementary material, which is available to authorized users.