Julie Y. Li

Follicular dendritic cell sarcoma (FDCS) is a rare malignant neoplasm commonly found in extranodal sites with unclear pathogenesis. Tumor cells typically exhibit a spindled morphology, whereas epithelioid morphology is rarely reported. Here, we have presented a rare biphasic FDCS with distinct immunophenotypic and molecular characteristics. A 63-year-old female presented with constipation and rectal bleeding. Imaging revealed an 11.4 cm lobulated enhancing soft tissue mass in the posterior pelvis. H&E sections revealed 2 sharply demarcated biphasic neoplastic populations: one population comprised spindled cells expressing CD21, CD23, CD35, clusterin, EMA, and D2-40; the other population consisted of epithelioid cells lacking CD21 and other FDC-associated markers except for focal weak clusterin expression. Both populations tested negative for CD163, CD68, S-100, langerin, CD1a, ALK-1, CD30, CD117, HMB45, Pan-CK, and EBER. The tumor was initially misdiagnosed as a collision (FDCS and perivascular epithelioid cell tumor) tumor. Molecular studies revealed a nearly identical mutational profile in both components confirming clonal identity and ruling out a composite tumor. In addition, low-level pathogenic mutations (variant allele frequency 2, indicating a more than 4-fold increase compared with a pooled normal control. Here, we have provided molecular characterization of biphasic FDCS. Prior such characterization seems to be unavailable in the literature.

Primary myelofibrosis (PMF) is a Philadelphia chromosome (Ph)-negative myeloproliferative neoplasm (MPN) that features clonal proliferation of atypical megakaryocytes and myeloid cells, fibrosis of the bone marrow, extramedullary hematopoiesis, and increased risk of leukemic transformation to acute myeloid leukemia (AML). With the widespread application of molecular studies, especially next generation sequencing (NGS), significant advances have reshaped our understanding of the molecular pathogenesis of PMF and the prognostic relevance of specific gene mutations. In this review, we summarize its clinicopathologic features, genetic and molecular findings, updated diagnostic criteria, and differential diagnosis. These updates have been incorporated into the 5th edition of the World Health Organization classification of Hematolymphoid Tumors (WHO-5th) and the 2022 International Consensus Classification (ICC), thereby improving diagnostic accuracy and risk stratification, both of which are essential for tailoring treatment strategies and enhancing patient outcomes.

Myeloproliferative neoplasms (MPNs) are a group of rare blood cancers characterized by the excessive production of blood cells in the bone marrow. These disorders arise from acquired genetic driver mutations, with or without underlying genetic predispositions, resulting in the uncontrolled production of red blood cells, white blood cells, or platelets. The excessive cell production and abnormal signaling from driver mutations cause chronic inflammation and a higher risk of blood clots and vascular complications. The primary goals of MPN treatment are to induce remission, improve quality of life and survival, as well as to reduce the risk of complications such as thrombosis, vascular events, and leukemic transformation. This review provides a comprehensive update on the diagnosis and therapeutic advancements in major MPN subtypes, including chronic myeloid leukemia, polycythemia vera, essential thrombocythemia, and primary myelofibrosis. It examines these complex diseases from a molecular and evolutionary perspective, highlighting key clinical trials’ long-term follow-up and therapies targeting driver mutations that have transformed treatment strategies. Additionally, several important advancements in addressing challenges such as anemia in myelofibrosis, along with promising emerging therapies, are also discussed.

Background: Chronic myeloid leukemia (CML) is characterized by the presence of BCR::ABL1 fusion gene resulting from a reciprocal translocation, t(9;22)(q34;q11.2), leading to prominent granulocytic proliferation. The majority of patients initially present in chronic phase (CP), which may progress to advanced CML with predominantly granulocytic phenotypes in the absence of proper treatment or response to tyrosine kinase inhibitors (TKIs). We present an exceptionally rare case in which an erythroid variant emerged from a CML patient resistant to multiple TKIs. This variant is characterized by the detection of t(9;22) BCR::ABL1 fusion in erythroid precursors at various maturation stages and the absence of granulocytic progenitor hyperplasia typically seen in classical CML. Case presentation: A 33-year-old female with CP-CML had received multiple TKI therapies since her initial diagnosis in 2015. Due to intolerable side effects and inconsistent adherence, she exhibited an inadequate response and developed new-onset pancytopenia. Bone marrow (BM) biopsy specimen revealed a hypercellular marrow with significant erythroid hyperplasia (90% of marrow cellularity) and a reversed myeloid-to-erythroid (M: E) ratio of 1:10. Both erythroid and myeloid cells displayed progressive maturation without dysplasia or excess blasts. Chromosomal analysis identified t(9;22) (q34;q11.2) in 19 out of 20 metaphase cells. BCR::ABL1 fusion transcript (p210 isoform) was confirmed by real-time quantitative polymerase chain reaction (RT-qPCR) and next-generation sequencing (NGS). Notably, no additional pathogenic cytogenetic abnormalities or ABL1 kinase domain mutations were detected. Here, we report the first published case of an erythroid variant emerging in a CML patient resistant to multiple TKIs—a distinct entity from the erythroid blast crisis evolving from CML. Conclusion: The erythroid variant of CML is distinguished by the presence of t(9;22) (q34;q11.2) BCR::ABL1 in predominant erythroid precursors at different stages of maturation. In a myeloid neoplasm showing predominant erythroid hyperplasia without typical CML features, it is vital to correlate morphology and t(9;22) BCR::ABL1 cytogenetic testing for accurate diagnosis, and to prevent confusion with PEL transformation in CML.

Plasmablastic myeloma (PBM) is an uncommon and aggressive morphologic variant of multiple myeloma (MM). The neoplastic immature cells exhibit diverse morphology, posing a diagnostic challenge. The diagnostic criteria for PBM include the identification of ≥ 2% plasmablasts in the bone marrow aspirate. This case describes the incidental finding of a light-chain multiple myeloma (LCMM) transformed into PBM, a phenomenon not previously reported.