Clonal evolution and relapse in early-stage follicular lymphoma - a tree with many branches†.

Follicular lymphoma (FL) is an indolent B-cell neoplasm characterised by multistep evolution from premalignant precursor cells carrying the hallmark t(14;18) translocation in the majority of cases. In a new article in The Journal of Pathology, samples of relapsed early-stage FL - primary manifestation and relapse with or without transformation - initially treated with radiotherapy only, were studied for clonal relationships and evolution. Using somatic mutations and the rearranged immunoglobulin sequences as markers, the majority of paired lymphoma samples showed so-called branched evolution from a common, possibly premalignant progenitor cell, with both shared and private mutations. In addition, clonally unrelated cases were identified. This and previous studies with similar findings clearly document that relapse or transformation of FL in many instances not necessarily represents a linear progression of disease due to acquisition of additional mutations and therapy resistance, but rather new outgrowths derived from a pool of clonally related, long-lived, and low proliferating precursor cells, or even unrelated second neoplasms. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Clonal origin and genomic diversity in Lynch syndrome-associated endometrial cancer with multiple synchronous tumors: Identification of the pathogenicity of MLH1 p.L582H.

Lynch syndrome-associated endometrial cancer patients often present multiple synchronous tumors and this assessment can affect treatment strategies. We present a case of a 27-year-old woman with tumors in the uterine corpus, cervix, and ovaries who was diagnosed with endometrial cancer and exhibited cervical invasion and ovarian metastasis. Her family history suggested Lynch syndrome, and genetic testing identified a variant of uncertain significance, MLH1 p.L582H. We conducted immunohistochemical staining, microsatellite instability analysis, and Sanger sequencing for Lynch syndrome-associated cancers in three generations of the family and identified consistent MLH1 loss. Whole-exome sequencing for the corpus, cervical, and ovarian tumors of the proband identified a copy-neutral loss of heterozygosity (LOH) occurring at the MLH1 position in all tumors. This indicated that the germline variant and the copy-neutral LOH led to biallelic loss of MLH1 and was the cause of cancer initiation. All tumors shared a portion of somatic mutations with high mutant allele frequencies, suggesting a common clonal origin. There were no mutations shared only between the cervix and ovary samples. The profiles of mutant allele frequencies shared between the corpus and cervix or ovary indicated that two different subclones originating from the corpus independently metastasized to the cervix or ovary. Additionally, all tumors presented unique mutations in endometrial cancer-associated genes such as ARID1A and PIK3CA. In conclusion, we demonstrated clonal origin and genomic diversity in a Lynch syndrome-associated endometrial cancer, suggesting the importance of evaluating multiple sites in Lynch syndrome patients with synchronous tumors.

Identification of RNF213 as a Potential Suppressor of Local Invasion in Intrahepatic Cholangiocarcinoma.

Intrahepatic cholangiocarcinoma (ICC) is a lethal cancer with poor survival especially when it spreads. The histopathology of its rare intraductal papillary neoplasm of the bile duct type (IPNB) characteristically shows cancer cells originating within the confined bile duct space. These cells eventually invade and infiltrate the nearby liver tissues, making it a good model to study the mechanism of local invasion, which is the earliest step of metastasis. To discover potential suppressor genes of local invasion in ICC, we analyzed the somatic mutation profiles and performed clonal evolution analyses of the 11 pairs of macrodissected locally invasive IPNB tissues (LI-IPNB) and IPNB tissues without local invasion from the same patients. We identified a protein-truncating variant in an E3 ubiquitin ligase, RNF213 (c.6967C>T; p.Gln2323X; chr17: 78,319,102 [hg19], exon 29), as the most common protein-truncating variant event in LI-IPNB samples (4/11 patients). Knockdown of RNF213 in HuCCT1 and YSCCC cells showed increased migration and invasion, and reduced vasculogenic mimicry but maintained normal proliferation. Transcriptomic analysis of the RNF213-knockdown vs control cells was then performed in the HuCCT1, YSCCC, and KKU-100 cells. Gene ontology enrichment analysis of the common differentially expressed genes revealed significantly altered cytokine and oxidoreductase-oxidizing metal ion activities, as confirmed by Western blotting. Gene Set Enrichment Analysis identified the most enriched pathways being oxidative phosphorylation, fatty acid metabolism, reactive oxygen species, adipogenesis, and angiogenesis. In sum, loss-of-function mutation of RNF213 is a common genetic alteration in LI-IPNB tissues. RNF213 knockdown leads to increased migration and invasion of ICC cells, potentially through malfunctions of the pathways related to inflammation and energy metabolisms.

Clonal expansion in normal tissues.

Cancer originates from a single ancestral cell that acquires a driver mutation, which confers a growth or survival advantage, followed by the acquisition of additional driver mutations by descendant cells. Recently, it has become evident that somatic cell mutations accumulate in normal tissues with aging and exposure to environmental factors, such as alcohol, smoking, and UV rays, increases the mutation rate. Clones harboring driver mutations expand with age, leading to tissue remodeling. Lineage analysis of myeloproliferative neoplasms and der(1;16)-positive breast cancer revealed that driver mutations were acquired early in our lives and that the development of cancer takes decades, unveiling the previously unknown early process of cancer development. Evidence that clonal hematopoiesis affects various diseases, including nonneoplastic diseases, highlights the potential role of the identification and functional analysis of mutated clones in unraveling unknown pathologies. In this review, we summarize the recent updates on clonal expansion in normal tissues and the natural history of cancer revealed through lineage analysis of noncancerous and cancerous tissues.

Relapse and transformation to myelodysplastic syndrome and acute myeloid leukemia following immunosuppressive therapy for aplastic anemia is more common as compared to allogeneic stem cell transplantation with a negative impact on survival.

We studied the incidence of relapse, transformation to myelodysplastic syndrome/acute myeloid leukemia, and survival in patients with aplastic anemia (AA) surviving more than 1 year after ATG/ALG-based immunosuppressive therapy (IST) between 1985 and 2020. Four-hundred seventy patients (413 adults and 57 children) were studied, and data were compared with 223 patients who underwent matched sibling donor transplant (MSD HSCT). Median follow-up is 50 months (12-359). Relapse occurred in 21.9% at a median time of 33.5 months (5-228) post IST. Twenty-six (5.5%) patients progressed to PNH, while 20 (4.3%) evolved to MDS/AML. Ten-year estimated overall survival (OS) is 80.9 ± 3% and was significantly better in patients without an event (85.1 ± 4%) compared to relapse (74.6% ± 6.2%) or clonal evolution (12.8% ± 11.8%) (p = 0.024). While the severity of AA (p = 0.011) and type of ATG (p = 0.028) used predicted relapse, only age at IST administration influenced clonal evolution (p = 0.018). Among HSCT recipients, relapse rates were 4.9% with no clonal evolution, and the 10-year OS was 94.5 ± 2%. In patients who survived 1 year following IST, outcomes were good except with clonal evolution to MDS/AML. These outcomes, however, were still inferior compared to matched sibling donor HSCT.

Superior detection of low-allele burden Janus kinase 2 V617F mutation and monitoring clonal evolution in myeloproliferative neoplasms using chip-based digital PCR.

The JAK2 V617F is a prevalent driver mutation in Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-MPNs), significantly affecting disease progression, immunophenotype, and patient outcomes. The World Health Organization (WHO) guidelines highlight the JAK2 V617F mutation as one of the key diagnostic criterions for Ph-MPNs. In this study, we analyzed 283 MPN samples with the JAK2 V617F mutation to assess the effectiveness of three detection technologies: chip-based digital PCR (cdPCR), real-time quantitative PCR (qPCR), and next-generation sequencing (NGS). Additionally, we investigated the relationship between JAK2 V617F mutant allele burden (% JAK2 V617F) and various laboratory characteristics to elucidate potential implications in MPN diagnosis. Our findings demonstrated high conformance of cdPCR with qPCR/NGS for detecting % JAK2 V617F, but the mutant allele burdens detected by qPCR/NGS were lower than those detected by cdPCR. Moreover, the cdPCR exhibited high sensitivity with a limit of detection (LoD) of 0.08% and a limit of quantification (LoQ) of 0.2% for detecting % JAK2 V617F in MPNs. Clinical implications were explored by correlating % JAK2 V617F with various laboratory characteristics in MPN patients, revealing significant associations with white blood cell counts, lactate dehydrogenase levels, and particularly ß2-microglobulin (ß2-MG) levels. Finally, a case report illustrated the application of cdPCR in detecting low-allele burdens in a de novo chronic myeloid leukemia (CML) patient with a hidden JAK2 V617F subclone, which expanded during tyrosine kinase inhibitor (TKI) treatment. Our findings underscore the superior sensitivity and accuracy of cdPCR, making it a valuable tool for early diagnosis and monitoring clonal evolution.

Relationship between clonal evolution and drug resistance in bladder cancer: A genomic research review.

Bladder cancer stands as a prevalent global malignancy, exhibiting notable sex-based variations in both incidence and prognosis. Despite substantial strides in therapeutic approaches, the formidable challenge of drug resistance persists. The genomic landscape of bladder cancer, characterized by intricate clonal heterogeneity, emerges as a pivotal determinant in fostering this resistance. Clonal evolution, encapsulating the dynamic transformations within subpopulations of tumor cells over time, is implicated in the emergence of drug-resistant traits. Within this review, we illuminate contemporary insights into the role of clonal evolution in bladder cancer, elucidating its influence as a driver in tumor initiation, disease progression, and the formidable obstacle of therapy resistance.

Pathogenic Variants Associated with Epigenetic Control and the NOTCH Pathway Are Frequent in Classic Hodgkin Lymphoma.

Classic Hodgkin lymphoma (cHL) constitutes a B-cell neoplasm derived from germinal center lymphocytes. Despite high cure rates (80-90%) obtained with the current multiagent protocols, a significant proportion of cHL patients experience recurrences, characterized by a lower sensitivity to second-line treatments. The genomic background of chemorefractory cHL is still poorly understood, limiting personalized treatment strategies based on molecular features. In this study, using a targeted next-generation sequencing (NGS) panel specifically designed for cHL research, we compared chemosensitive and chemorefractory diagnostic tissue samples of cHL patients. Furthermore, we longitudinally examined paired diagnosis-relapsesamples of chemorefractory cHL in order to define patterns of dynamic evolution and clonal selection. Pathogenic variants in NOTCH1 and NOTCH2 genes frequently arise in cHL. Mutations in genes associated with epigenetic regulation (CREBBP and EP300) are particularly frequent in relapsed/refractory cHL. The appearance of novel clones characterized by mutations previously not identified at diagnosis is a common feature in cHL cases showing chemoresistance to frontline treatments. Our results expand current molecular and pathogenic knowledge of cHL and support the performance of molecular studies in cHL prior to the initiation of first-line therapies.

FLT3-TKD Measurable Residual Disease Detection Using Droplet Digital PCR and Clinical Applications in Acute Myeloid Leukemia.

The tyrosine kinase domain of the FMS-Like tyrosine kinase 3 (FLT3-TKD) is recurrently mutated in acute myeloid leukemia (AML). Common molecular techniques used in its detection include PCR and capillary electrophoresis, Sanger sequencing and next-generation sequencing with recognized sensitivity limitations. This study aims to validate the use of droplet digital PCR (ddPCR) in the detection of measurable residual disease (MRD) involving the common FLT3-TKD mutations (D835Y, D835H, D835V, D835E). Twenty-two diagnostic samples, six donor controls, and a commercial D835Y positive control were tested using a commercial Bio-rad® ddPCR assay. All known variants were identified, and no false positives were detected in the wild-type control (100% specificity and sensitivity). The assays achieved a limit of detection suitable for MRD testing at 0.01% variant allelic fraction. Serial samples from seven intensively-treated patients with FLT3-TKD variants at diagnosis were tested. Five patients demonstrated clearance of FLT3-TKD clones, but two patients had FLT3-TKD persistence in the context of primary refractory disease. In conclusion, ddPCR is suitable for the detection and quantification of FLT3-TKD mutations in the MRD setting; however, the clinical significance and optimal management of MRD positivity require further exploration.

[Role of Telomere in Clonal Evolution of Acquired Aplastic Anemia--Review].

Studies have found that 1/3 patients with acquired aplastic anemia have shortened telomere length, and the shorter the telomere, the longer the disease course, the more prone to relapse, the lower the overall survival rate, and the higher the probability of clonal evolution. The regulation of telomere length is affected by many factors, including telomerase activity, telomerase-related genes, telomere regulatory proteins and other related factors. Telomere shortening can lead to genetic instability and increases the probability of clonal evolution in patients with acquired aplastic anemia. This article reviews the role of telomere in the clonal evolution of acquired aplastic anemia and factors affecting telomere length.

Clonal evolution process from essential thrombocythemia to acute myeloid leukemia in the original patient from whom the CALR-mutated Marimo cell line was established.

We previously reported the Marimo cell line, which was established from the bone marrow cells of a patient with essential thrombocythemia (ET) at the last stage after transformation to acute myeloid leukemia (AML). This cell line is widely used for the biological analysis of ET because it harbors CALR mutation. However, genetic processes during disease progression in the original patient were not analyzed. We sequentially analyzed the genetic status in the original patient samples during disease progression. The ET clone had already acquired CALR and MPL mutations, and TP53 and NRAS mutations affected the disease progression from ET to AML in this patient. Particularly, the variant allele frequency of the NRAS mutation increased along with the disease progression after transformation, and the NRAS-mutated clone selectively proliferated in vitro, resulting in the establishment of the Marimo cell line. Although CALR and MPL mutations co-existed, MPL was not expressed in Marimo cells or any clinical samples. Furthermore, mitogen-activated protein kinase (MAPK) but not the JAK2-STAT pathway was activated. These results collectively indicate that MAPK activation is mainly associated with the proliferation ability of Marimo cells.

Unraveling trajectories from aplastic anemia to hematologic malignancies: genetic and molecular insights.

Background: Aplastic anemia (AA), characterized by hematopoietic stem cell deficiency, can evolve into different hematologic malignancies. Our understanding of the genetic basis and mechanisms of this progression remains limited. Methods: We retrospectively studied 9 acquired AA patients who later developed hematologic malignancies. Data encompassed clinical, laboratory, karyotype, and next-generation sequencing (NGS) information. We explored chromosomal alterations and mutation profiles to uncover genetic changes underlying the transition. Results: Nine AA patients developed myelodysplastic syndrome (seven patients), acute myeloid leukemia (one patient), or chronic myelomonocytic leukemia (one patient). Among eight patients with karyotype results at secondary malignancy diagnosis, monosomy 7 was detected in three. Trisomy 1, der(1;7), del(6q), trisomy 8, and del(12p) were detected in one patient each. Among three patients with NGS results at secondary malignancy diagnosis, KMT2C mutation was detected in two patients. Acquisition of a PTPN11 mutation was observed in one patient who underwent follow-up NGS testing during progression from chronic myelomonocytic leukemia to acute myeloid leukemia. Conclusion: This study highlights the genetic dynamics in the progression from AA to hematologic malignancy. Monosomy 7's prevalence and the occurrence of PTPN11 mutations suggest predictive and prognostic significance. Clonal evolution underscores the complexity of disease progression.

Single-cell lineage tracing with endogenous markers.

Resolving lineage relationships between cells in an organism provides key insights into the fate of individual cells and drives a fundamental understanding of the process of development and disease. A recent rapid increase in experimental and computational advances for detecting naturally occurring somatic nuclear and mitochondrial mutation at single-cell resolution has expanded lineage tracing from model organisms to humans. This review discusses the advantages and challenges of experimental and computational techniques for cell lineage tracing using somatic mutation as endogenous DNA barcodes to decipher the relationships between cells during development and tumour evolution. We outlook the advantages of spatial clonal evolution analysis and single-cell lineage tracing using endogenous genetic markers.

Unveiling the dynamics and molecular landscape of a rare chronic lymphocytic leukemia subpopulation driving refractoriness: insights from single-cell RNA sequencing.

Early identification of resistant cancer cells is currently a major challenge, as their expansion leads to refractoriness. To capture the dynamics of these cells, we made a comprehensive analysis of disease progression and treatment response in a chronic lymphocytic leukemia (CLL) patient using a combination of single-cell and bulk genomic methods. At diagnosis, the patient presented with unfavorable genetic markers, including notch receptor 1 (NOTCH1) mutation and loss(11q). The initial and subsequent treatment lines did not lead to a durable response and the patient developed refractory disease. Refractory CLL cells featured substantial dysregulation in B-cell phenotypic markers such as human leukocyte antigen (HLA) genes, immunoglobulin (IG) genes, CD19 molecule (CD19), membrane spanning 4-domains A1 (MS4A1; previously known as CD20), CD79a molecule (CD79A) and paired box 5 (PAX5), indicating B-cell de-differentiation and disease transformation. We described the clonal evolution and characterized in detail two cell populations that emerged during the refractory disease phase, differing in the presence of high genomic complexity. In addition, we successfully tracked the cells with high genomic complexity back to the time before treatment, where they formed a rare subpopulation. We have confirmed that single-cell RNA sequencing enables the characterization of refractory cells and the monitoring of their development over time.

The FGF6 amplification mutation plays an important role in the progression and treatment of malignant meningioma.

Meningioma is a benign tumor with slow growth and long course. However, patients with recurrent malignant meningioma still face a lack of effective treatment. Here, we report a rare case of primary mediastinal malignant meningioma with lung and bone metastases, who benefited from the treatment of apatinib (≥33 months) and anlotinib (until the publication date). Retrospective molecular analysis revealed the frequent amplification of FGF6 in primary and metastatic lesions. Then we constructed the FGF6 over-expressed IOMM-LEE and CH157MN malignant meningioma cell lines, and in vitro and vivo experiments showed that overexpression of FGF6 can promote the proliferation, migration and invasion of malignant meningioma cells. Based on the Western analysis, we revealed that FGF6 can promote the phosphorylation of FGFR, AKT, and ERK1/2, which can be inhibited by anlotinib. Together, we were the first to verify that overexpression of FGF6 promotes the progression of malignant meningiomas by activating FGFR/AKT/ERK1/2 pathway and pointed out that anlotinib may effectively inhibit the disease progression of patients with FGF6 amplification.

Longitudinal Comparative Analysis of Circulating Tumor DNA and Matched Tumor Tissue DNA in Patients with Metastatic Colorectal Cancer Receiving Palliative First-Line Systemic Anti-Cancer Therapy.

Purpose: This study aimed to compare tumor tissue DNA (ttDNA) and circulating tumor DNA (ctDNA) to explore the clinical applicability of ctDNA and to better understand clonal evolution in patients with metastatic colorectal cancer undergoing palliative first-line systemic therapy. Materials and Methods: We performed targeted sequencing analysis of 88 cancer-associated genes using germline DNA, ctDNA at baseline (baseline-ctDNA), and ctDNA at progressive disease (PD-ctDNA). The results were compared with ttDNA data. Results: Among 208 consecutively enrolled patients, we selected 84 (41 males; median age 59, range 35 to 90) with all four sample types available. A total of 202 driver mutations were found in 34 genes. ttDNA exhibited the highest mutation frequency (n=232), followed by baseline-ctDNA (n=155) and PD-ctDNA (n=117). Sequencing ctDNA alongside ttDNA revealed additional mutations in 40 patients (47.6%). PD-ctDNA detected 13 novel mutations in 10 patients (11.9%) compared to ttDNA and baseline-ctDNA. Notably, 7 mutations in 5 patients (6.0%) were missense or nonsense mutations in APC, TP53, SMAD4, and CDH1 genes. In baseline-ctDNA, higher maximal variant allele frequency (VAF) values (p=0.010) and higher VAF values of APC (p=0.012), TP53 (p=0.012), and KRAS (p=0.005) mutations were significantly associated with worse overall survival. Conclusion: While ttDNA remains more sensitive than ctDNA, our ctDNA platform demonstrated validity and potential value when ttDNA was unavailable. Post-treatment analysis of PD-ctDNA unveiled new pathogenic mutations, signifying cancer's clonal evolution. Additionally, baseline-ctDNA's VAF values were prognostic after treatment.

Differential Competitive Growth of Transgenic Subclones of Neuroblastoma Cells Expressing Different Levels of Cathepsin D Co-Cultured in 2D and 3D in Response to EGF: Implications in Tumor Heterogeneity and Metastasis.

Neuroblastoma (NB) is an embryonal tumor arising from the sympathetic central nervous system. The epidermal growth factor (EGF) plays a role in NB growth and metastatic behavior. Recently, we have demonstrated that cathepsin D (CD) contrasts EGF-induced NB cell growth in 2D by downregulating EGFR/MAPK signaling. Aggressive NB is highly metastatic to the bone and the brain. In the metastatic process, adherent cells detach to form clusters of suspended cells that adhere once they reach the metastatic site and form secondary colonies. Whether CD is involved in the survival of metastatic NB clones is not known. Therefore, in this study, we addressed how CD differentially affects cell growth in suspension versus the adherent condition. To mimic tumor heterogeneity, we co-cultured transgenic clones silenced for or overexpressing CD. We compared the growth kinetics of such mixed clones in 2D and 3D models in response to EGF, and we found that the Over CD clone had an advantage for growth in suspension, while the CD knocked-down clone was favored for the adherent growth in 2D. Interestingly, on switching from 3D to 2D culture conditions, the expression of E-cadherin and of N-cadherin increased in the KD-CD and Over CD clones, respectively. The fact that CD plays a dual role in cancer cell growth in 2D and 3D conditions indicates that during clonal evolution, subclones expressing different level of CD may arise, which confers survival and growth advantages depending on the metastatic step. By searching the TCGA database, we found up to 38 miRNAs capable of downregulating CD. Interestingly, these miRNAs are associated with biological processes controlling cell adhesion and cell migration. The present findings support the view that during NB growth on a substrate or when spreading as floating neurospheres, CD expression is epigenetically modulated to confer survival advantage. Thus, epigenetic targeting of CD could represent an additional strategy to prevent NB metastases.

Myelodysplastic neoplasms evolving from inherited bone marrow failure syndromes / germline predisposition syndromes: Back under the microscope.

Inherited bone marrow failure syndromes and germline predisposition syndromes (IBMFS/GPS) are associated with increased risk for hematologic malignancies, particularly myeloid neoplasms, such as myelodysplastic neoplasms (MDS) and acute myeloid leukemia (AML). The diagnosis of MDS in these syndromes poses difficulty due to frequent bone marrow hypocellularity and the presence of some degree of dysplastic features related to the underlying germline defect causing abnormal maturation of one or more cell lines. Yet, the diagnosis of MDS is usually associated with a worse outcome in several IBMFS/GPS. Criteria for the diagnosis of MDS in IBMFS/GPS have not been standardized with some authors suggesting a mixture of morphologic, cytogenetic, and genetic criteria. This review highlights these challenges and suggests a more standardized approach to nomenclature and diagnostic criteria.

From primary myelofibrosis to chronic myeloid leukemia, BCR::ABL1+ B-Lymphoblastic leukemia, and back to primary myelofibrosis: An illustration of dynamic clonal evolution.

The simultaneous detection of BCR::ABL1 and JAK2 V617F was rarely reported and their clonal relationship and dynamic clonal shift were not characterized. Here, we described a unique case with the initial presentation as JAK2 V617F+ primary myelofibrosis, followed by the emergence of BCR::ABL1+ chronic myeloid leukemia. The patient then developed BCR::ABL1+ B-lymphoblastic leukemia. Treatment for B-lymphoblastic leukemia prompted a regression to the state of primary myelofibrosis. In light of these observations, we proposed a clonal evolution model for this case.

Transformation of t(14;18)-negative follicular lymphoma to plasmablastic lymphoma: a case report with analysis of genetic evolution.

BACKGROUND: Follicular lymphoma (FL) is characterized by t(14;18)(q32;q21) involving the IGH and BCL2 genes. However, 10-15% of FLs lack the BCL2 rearrangement. These BCL2-rearrangement-negative FLs are clinically, pathologically, and genetically heterogeneous. The biological behavior and histological transformation of such FLs are not adequately characterized. Here, we report the first case of t(14;18)-negative FL that rapidly progressed to plasmablastic lymphoma (PBL). CASE PRESENTATION: A previously healthy 51-year-old man presented with leg swelling. Computed tomography (CT) showed enlarged lymph nodes (LNs) throughout the body, including both inguinal areas. Needle biopsy of an inguinal LN suggested low-grade B-cell non-Hodgkin lymphoma. Excisional biopsy of a neck LN showed proliferation of centrocytic and centroblastic cells with follicular and diffuse growth patterns. Immunohistochemical analysis showed that the cells were positive for CD20, BCL6, CD10, and CD23. BCL2 staining was negative in the follicles and weak to moderately positive in the interfollicular areas. BCL2 fluorescence in situ hybridization result was negative. Targeted next-generation sequencing (NGS) revealed mutations in the TNFRSF14, CREBBP, STAT6, BCL6, CD79B, CD79A, and KLHL6 genes, without evidence of BCL2 or BCL6 rearrangement. The pathologic and genetic features were consistent with t(14;18)-negative FL. Two months after one cycle of bendamustine and rituximab chemotherapy, the patient developed left flank pain. Positron emission tomography/CT showed new development of a large hypermetabolic mass in the retroperitoneum. Needle biopsy of the retroperitoneal mass demonstrated diffuse proliferation of large plasmablastic cells, which were negative for the B-cell markers, BCL2, BCL6, and CD10; they were positive for MUM-1, CD138, CD38, and C-MYC. The pathologic findings were consistent with PBL. The clonal relationship between the initial FL and subsequent PBL was analyzed via targeted NGS. The tumors shared the same CREBBP, STAT6, BCL6, and CD79B mutations, strongly suggesting that the PBL had transformed from a FL clone. The PBL also harbored BRAF V600E mutation and IGH::MYC fusion in addition to IGH::IRF4 fusion. CONCLUSIONS: We propose that transformation or divergent clonal evolution of FL into PBL can occur when relevant genetic mutations are present. This study broadens the spectrum of histological transformation of t(14;18)-negative FL and emphasizes its biological and clinical heterogeneity.