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Pathologic diagnosis of mesothelioma continues to evolve. These updated guidelines (1) reflect the authors' expert opinion, informed by a thorough review of relevant literature. The contents were discussed at the [...], * Context.--Mesothelioma is an uncommon tumor that can be difficult to diagnose. Objective.--To provide updated, practical guidelines for the pathologic diagnosis of mesothelioma. Data Sources.--Pathologists involved in the International Mesothelioma Interest Group and others with expertise in mesothelioma contributed to this update. Reference material includes peer-reviewed publications and textbooks. Conclusions.--There was consensus opinion regarding guidelines for (1) histomorphologic diagnosis of mesothelial tumors, including distinction of epithelioid, biphasic, and sarcomatoid mesothelioma; recognition of morphologic variants and patterns; and recognition of common morphologic pitfalls; (2) molecular pathogenesis of mesothelioma; (3) application of immunohistochemical markers to establish mesothelial lineage and distinguish mesothelioma from common morphologic differentials; (4) application of ancillary studies to distinguish benign from malignant mesothelial proliferations, including BAP1 and MTAP immunostains; novel immunomarkers such as Merlin and p53; fluorescence in situ hybridization (FISH) for homozygous deletion of CDKN2A; and novel molecular assays; (5) practical recommendations for routine reporting of mesothelioma, including grading epithelioid mesothelioma and other prognostic parameters; (6) diagnosis of mesothelioma in situ; (7) cytologic diagnosis of mesothelioma, including use of immunostains and molecular assays; and (8) features of nonmalignant peritoneal mesothelial lesions. (Arch Pathol Lab Med. 2024;148:1251-1271; doi: 10.5858/arpa.2023-0304-RA)

Anti-neutrophil cytoplasmic antibody-associated vasculitides (AAV) represent a heterogeneous multisystem group of disorders typified by necrotising inflammation of smaller blood vessels, classically yielding a pauci-immune, crescentic glomerulonephritis. Without prompt treatment, there is a significant risk of irreversible damage and ensuing renal impairment. Diagnosis is often challenging, exacerbated by the disorder’s often vague and insidious presentation. Even with known AAV, relapse can mimic other similarly serious conditions including infection or malignancy, with significant ramifications on respective downstream management options. Here, we present the case of a young man with pre-existing myeloperoxidase-positive vasculitis, describing a subacute cluster of symptoms and subsequently found to have an anterior mediastinal mass. Urgent tissue sampling excluded other aetiologies and ultimately delineated this as a surprising complication of vasculitis, allowing for prompt immunosuppression escalation. This case highlights the diagnostic challenge these patients represent, and the utility timely access to multimodality imaging holds alongside a multidisciplinary approach to expedite correct management decisions. [ABSTRACT FROM AUTHOR]

Background: The morbidity and mortality from AL amyloidosis has significantly improved with the development of novel treatments. Daratumumab is a highly effective treatment for AL amyloidosis, but end-stage kidney disease is a common complication of this condition. Kidney transplantation is the ideal form of renal replacement therapy but has historically been contraindicated in this group of patients. Methods: Given the improved survival and better treatments of both conditions, we argue that it is time to reconsider transplanting these patients. Results: We report our experience of transplanting four patients with AL amyloidosis who had achieved stable remission through treatment with daratumumab. Conclusions: We highlight the key challenges involved and discuss important clinical issues for patients receiving daratumumab, particularly the difficulties with interpreting the crossmatch in light of daratumumab and immunoglobulin therapy interference. We also discuss the complexities involved in balancing the risks of infection, relapse, rejection, and immunosuppression in such patients. [ABSTRACT FROM AUTHOR]

Metastatic uveal melanoma (UM) is a devastating disease with few treatment options. We evaluated the safety, tolerability and preliminary activity of arginine depletion using pegylated arginine deiminase (ADI‐PEG20; pegargiminase) combined with pemetrexed (Pem) and cisplatin (Cis) chemotherapy in a phase 1 dose‐expansion study of patients with argininosuccinate synthetase (ASS1)‐deficient metastatic UM. Eligible patients received up to six cycles of Pem (500 mg/m2) and Cis (75 mg/m2) every 3 weeks plus weekly intramuscular ADI (36 mg/m2), followed by maintenance ADI until progression (NCT02029690). Ten of fourteen ASS1‐deficient patients with UM liver metastases and a median of one line of prior immunotherapy received ADIPemCis. Only one ≥ grade 3 adverse event of febrile neutropenia was reported. Seven patients had stable disease with a median progression‐free survival of 3.0 months (range, 1.3–8.1) and a median overall survival of 11.5 months (range, 3.2–36.9). Despite anti‐ADI‐PEG20 antibody emergence, plasma arginine concentrations remained suppressed by 18 weeks with a reciprocal increase in plasma citrulline. Tumour rebiopsies at progression revealed ASS1 re‐expression as an escape mechanism. ADIPemCis was well tolerated with modest disease stabilisation in metastatic UM. Further investigation of arginine deprivation is indicated in UM including combinations with immune checkpoint blockade and additional anti‐metabolite strategies. [ABSTRACT FROM AUTHOR]