TRBC1 in flow cytometry: Assay development, validation, and reporting considerations.

The assessment of T-cell clonality by flow cytometry has long been suboptimal, relying on aberrant marker expression and/or intensity. The introduction of TRBC1 shows much promise for improving the diagnosis of T-cell neoplasms in the clinical flow laboratory. Most laboratories considering this marker already have existing panels designed for T-cell workups and will be determining how best to incorporate TRBC1. We present this comprehensive summary of TRBC1 and supplemental case examples to familiarize the flow cytometry community with its potential for routine application, provide examples of how to incorporate it into T-cell panels, and signal caution in interpreting the results in certain diagnostic scenarios where appropriate.

Novel ELANE Mutation Associated with a Clinical Presentation of Cyclic Neutropenia.

OBJECTIVES: Congenital neutropenia, defined by absolute neutrophil count (ANC) 2.5x109/L in infants, includes a variety of genotypic alterations that manifest with chronic immunodeficiency and, as a result, presents in infancy with recurrent infections. The gene that encodes neutrophil elastase, ELANE, has pathological variants yielding two distinct phenotypes: severe congenital neutropenia (SCN) and cyclic neutropenia (CyN). While SCN exhibits persistent pathologic ANC values, CyN exhibits pathologic ANC values in a patterned fashion which can recur in 21-day intervals. Here, we describe a patient with a novel heterozygous ELANE deletion (c.224+(4_19)del16) presenting with clinical features consistent with CyN and a response to first-line therapy of granulocyte colony- stimulating factor.

PCNEO, a New Proficiency Testing Program for Flow Cytometric Analysis of Plasma Cell Neoplasms From the College of American Pathologists Diagnostic Immunology and Flow Cytometry Committee.

CONTEXT.­: In 2018 the College of American Pathologists Diagnostic Immunology and Flow Cytometry Committee designed and implemented a new plasma cell neoplasia flow cytometry proficiency testing program-PCNEO-to allow clinical flow cytometry laboratories to monitor and assess their performance compared with a peer group. OBJECTIVE.­: To report the results from the first 4 years of the PCNEO program. DESIGN.­: Program participants were sent 2 sets of challenges per year, each including 1 wet challenge and 2 dry challenges, with associated clinical and laboratory findings. The wet challenges were composed of myeloma cell line specimens (with or without dilution in preserved whole blood) for flow cytometric analysis. The dry (paper) challenges were composed of clinical case summaries and images of flow cytometric test results from various flow cytometry laboratories of committee members. RESULTS.­: A total of 116 to 145 laboratories from 17 countries enrolled in the proficiency testing program. For the wet challenges, almost all participants (97%-100%; cumulative, 98.2%) correctly identified the presence of neoplastic plasma cell populations based on flow cytometric analysis of undiluted myeloma cell lines. Slightly fewer participants (89.0%-97.4%; cumulative, 95.2%) correctly identified the presence of neoplastic plasma cell populations based on flow cytometric analysis of diluted myeloma cell lines (10% or 50% dilutions into peripheral blood) intended to better represent a typical clinical sample. There was generally agreement among 80% or more of participants for positive or negative staining for CD38, CD138, CD19, CD20, and surface and cytoplasmic κ and λ light chains. Similarly, 84% to 100% of participants were able to correctly identify the presence of neoplastic plasma cell populations in paper challenges, including the presence of small, neoplastic plasma cell populations (0.01%-5.0% clonal plasma cells), or the presence of nonneoplastic plasma cell populations (correctly identified by 91%-96% of participants). CONCLUSIONS.­: Participant performance in the new proficiency testing program was excellent overall, with the vast majority of participants able to perform flow cytometric analysis and identify neoplastic plasma cell populations, and to identify small plasma cell clones or expanded populations of reactive plasma cells in dry challenge flow cytometry results. This program will allow laboratories to verify the accuracy of their testing program and test interpretations for the assessment of patients suspected of having a plasma cell neoplasm.

Summary of validation considerations with real-life examples using both qualitative and semiquantitative flow cytometry assays.

In the clinical laboratory, flow cytometry assays are critical to providing diagnostic and prognostic information to the treating clinicians. A validation or verification provides confidence that the assay will yield reliable results that can be trusted to make critical medical decisions. The following performance specifications should be included in a validation for laboratory developed tests as needed: accuracy (or trueness), precision (reproducibility and repeatability), detection capability, selectivity, reference range, and sample and reagent stability. We define these terms and present our approach to validation of several common flow cytometry assays, including examples of a leukemia/lymphoma assay and a paroxysmal nocturnal hemoglobinuria (PNH) assay.

Myelodysplastic Syndrome with Excess Blasts 2 (MDS-EB-2): A Historical Overview and Review of Forthcoming Classifications.

OBJECTIVES: Myelodysplastic syndrome with excess blasts-2 (MDS-EB-2) primarily affects adults older than 50 years and confers a worse prognosis with a higher risk of transformation to acute myeloid leukemia (AML) compared to myelodysplastic syndrome (MDS) and MDS with excess blasts-1 (MDS-EB-1). In ordering diagnostic studies for MDS, cytogenetic and genomic studies are vital as they have significant clinical and prognostic implications for the patient. We present a case of a 71-year-old male diagnosed with MDS-EB-2 with a pathogenic loss-of-function TP53 variant and discuss presentation, pathogenesis, and the importance of thorough diagnostic testing through multiple modalities to accurately diagnose and subtype MDS. In addition, we explore a historical overview of the diagnostic criteria of MDS-EB-2 and how it has changed over time from the World Health Organization (WHO) 4th edition in 2008, the WHO revised 4th edition in 2017, and the upcoming WHO 5th edition and International Consensus Classification (ICC) for 2022.

Multiple Myeloma Detected by Noninvasive Prenatal Testing.

OBJECTIVES: Noninvasive prenatal testing (NIPT) has become a widely used screening method to detect fetal aneuploidies using cell-free fetal DNA (cffDNA) obtained from maternal blood. It is noninvasive, highly sensitive and specific, and can be offered in the first trimester of pregnancy. Though the goal of NIPT is to detect abnormalities in fetal DNA, occasionally abnormalities are detected that are not attributable to the fetus. Tumor DNA is laden with abnormalities and, rarely, NIPT has detected occult malignancy in the mother. Maternal malignancy in pregnancy is relatively uncommon, estimated at 1 in 1,000 pregnant women. We present a case of a 38-year-old woman diagnosed with multiple myeloma after abnormal NIPT testing results.

Noninvasive Prenatal Testing Leading to a Diagnosis of Hodgkin Lymphoma.

OBJECTIVES: Noninvasive prenatal testing (NIPT) is a screening method used to detect the most common fetal aneuploidies using cell-free fetal DNA (cffDNA) obtained from maternal blood. Due to the high sensitivity and specificity, low false positive rate, and use as early as 10-weeks' gestation NIPT has been rapidly integrated into prenatal care. While NIPT is an excellent screening tool, the results can be influenced by many factors including placental mosaicism, maternal aneuploidy or mosaicism, and occult maternal malignancy. The diagnosis and treatment of malignancy during pregnancy present many challenges ranging from the use of imaging techniques to the delivery of optimal therapy, weighing the unique risks to both the mother and the fetus. We present a case of a 30-year-old woman diagnosed with Hodgkin lymphoma after NIPT and outline the challenges in diagnosis and treatment of malignancy occurring during pregnancy.

Mantle Cell Lymphoma Presenting with Cutaneous Lesions: A Rare Manifestation of a Systemic Disease.

OBJECTIVES: Cutaneous lymphoma is a broad term used to describe any type of lymphoma involving the skin. They may be primary, arising in the skin, or secondary, resulting from spread of a systemic lymphoma. Cutaneous involvement of mantle cell lymphoma (MCL) is extremely rare and most often occurs secondarily. To date, less than 100 cases of MCL involving the skin have been described in the English literature. We describe a case of MCL involving the skin as the clinical presentation of disease in a 74-year-old man and highlight the radiographic and pathologic findings, treatment course, and prognosis.

Acute Myeloid Leukemia with Myelodysplasia-Related Changes Presenting as Vitamin B12 Deficiency: A Cautionary Tale.

OBJECTIVES: Acute myeloid leukemia may present with significant dysmyelopoiesis within the peripheral blood smear and bone marrow aspirate. In the setting of Vitamin B12 deficiency, proliferation of a clonal population of malignant cells can become impaired, masking an underlying myelodysplastic or leukemic process. Typically, the cautionary tale warns against diagnosing acute myeloid leukemia before ruling out Vitamin B12 deficiency. Here we describe a patient who initially presented with pancytopenia and Vitamin B12 deficiency who, upon supplementation, developed overt acute myeloid leukemia. This case will highlight the importance of cytogenetic and molecular studies as essential diagnostic tools in patients with unique presentations.

Mantle cell lymphoma presenting with lethal atraumatic splenic rupture.

Mantle cell lymphoma is characterized by t(11;14) with CCND1-IGH fusion and manifests with a spectrum of disease ranging from relatively indolent to aggressive. Here, we present a case of pleomorphic mantle cell lymphoma with three fusion signals that presented with lethal atraumatic splenic rupture. We discuss on the implications of variant CCND1 signal patterns as well as the epidemiology and pathophysiology of atraumatic splenic rupture.

Solving the Puzzle: The Diagnosis of Atypical Chronic Myeloid Leukemia, BCR-ABL1-Negative (aCML).

OBJECTIVES: Atypical chronic myeloid leukemia, BCR-ABL1-negative (aCML), is a rare myelodysplastic/myeloproliferative neoplasm with heterogeneous clinical and genetic features, a high rate of transformation to acute myeloid leukemia (AML), and poor survival rate. The diagnosis of aCML is a diagnosis of exclusion and requires the fulfillment of strict diagnostic criteria. Until recently, there were no distinctive cytogenetic or molecular abnormalities for aCML adding to the diagnostic challenge. We present a case of aCML and highlight the pertinent clinical, morphological, and genetic features required for the diagnosis.

Unintended Consequences: Therapy-Related Acute Myeloid Leukemia.

OBJECTIVES: Acute myeloid leukemia (AML) is a group of diseases resulting from a clonal expansion of myeloid precursor cells in the bone marrow. Each subtype harbors characteristic clinical, morphologic, and molecular features. AML is most often de novo and arises from somatic mutations causing unchecked proliferation of myeloblasts, but it may also present as a secondary malignancy, often as the result of prior cytotoxic exposure. Here we present a case of therapy-related AML (t-AML) following chemotherapy exposure found to have a characteristic balanced translocation involving 11q23 and outline a potential mechanism of oncogenesis.

Mantle cell lymphoma presenting with lethal atraumatic splenic rupture

Mantle cell lymphoma is characterized by t(11;14) with CCND1-IGH fusion and manifests with a spectrum of disease ranging from relatively indolent to aggressive. Here, we present a case of pleomorphic mantle cell lymphoma with three fusion signals that presented with lethal atraumatic splenic rupture. We discuss on the implications of variant CCND1 signal patterns as well as the epidemiology and pathophysiology of atraumatic splenic rupture.

Acute Myeloid Leukemia with t(8;16)(p11.2;p13.3)/ KAT6A-CREBBP in a Patient with an NF1 Germline Mutation and Clinical Presentation Mimicking Acute Promyelocytic Leukemia.

OBJECTIVES: Acute myeloid leukemia (AML) with t(8;16)(p11.2;p13.3)/KAT6A-CREBBP is an uncommon subtype of AML accounting for less than 0.5% of AML cases. AML with t(8;16)/KAT6A-CREBBP has characteristic clinical and pathologic features including disseminated intravascular coagulation (DIC), leukemia cutis, hemophagocytosis, monocytic or myelomonocytic differentiation, is frequently associated with therapy-related AML and has a poor prognosis. We present a classic case of AML with t(8;16)/KAT6A-CREBBP occurring in a patient with both a germline NF1 mutation and recent cytotoxic therapy for embryonal rhabdomyosarcoma.

Educational Case: Cytogenetics.

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, see http://journals.sagepub.com/doi/10.1177/2374289517715040.1.

Acute Myeloid Leukemia with t(6;9)(p23;q34.1); DEK-NUP214: The Pathogenesis and Potential.

OBJECTIVES: Acute myeloid leukemia (AML) is caused by the arrested differentiation and dysregulated proliferation of myeloid precursors. Many AMLs harbor genetic abnormalities which determine the molecular mechanisms of the disease and are associated with distinct clinical and pathological features, prognosis, and targeted therapies. We present a case of acute myeloid leukemia with t(6;9)(p23;q34.1) and review the classic clinical presentations and underlying pathogenesis of the disease.