Nodal T-Cell Lymphoma Transdifferentiated from Mantle Cell Lymphoma with Epstein-Barr Virus Infection

Lineage plasticity is the ability of cells to transition from one committed phenotype to another. Lineage plasticity and resultant lineage switch are not uncommon in the context of development and cancers. The term “lineage switch” in cancer implies a clonal relationship between the original neoplasm and the newer, post-switch neoplasm. It is distinct from a secondary neoplasm, meaning a genetically unrelated second neoplasm arising in the same patient. It is also distinct from the phenomenon of one lymphoid neoplasm arising in the abnormal inflammatory milieu associated with another, clonally unrelated lymphoid neoplasm. An EBV-driven B-cell lymphoma arising in the background of T-follicular helper cell lymphoma would not be considered lineage switch [1].

True lineage switch is a well-documented phenomenon but is largely limited to certain specific contexts. Lineage switch from lymphoid to myeloid leukemia is well described [2]. In some cases, this occurs following treatment with monoclonal antibodies or CAR-T cells directed against B-cell antigens, such as CD20, CD19, or CD79a [3]. Histiocytic neoplasms arising after or alongside B-cell neoplasms are thought develop from the B-cell neoplasm itself or from a lymphoid progenitor common to both [4]. However, this case demonstrates lineage switch from a mantle cell lymphoma (MCL), a mature B-cell lymphoma, to a T-cell lymphoma, an almost unheard of phenomenon that to our knowledge has been previously reported only twice in the literature. Interestingly, the MCL cells in this case were EBV-infected and had a transformed, Reed-Sternberg (RS)-like morphology, which is in itself rare but not unprecedented [5]. The degree to which EBV infection may have influenced or potentiated the switch is unclear.

The patient (male) had no significant past medical history prior to presentation to an outside institution at age 46 with leukocytosis (27,000 cells/μL) and hepatosplenomegaly. He underwent bone marrow biopsy at the outside institution and was diagnosed with MCL, reportedly positive for cyclin D1 and negative for SOX11 by immunohistochemistry, and FISH positive for CCND1::IGH. Overall, the presentation was consistent with the leukemic non-nodal variant of MCL. He was not initially treated; however, he underwent splenectomy about 2 years post-diagnosis. Approximately 7 years post-diagnosis, he developed uveal involvement by MCL and was initiated on ibrutinib.

He presented to our institution 9 years after initial diagnosis, while on ibrutinib, with night sweats and left groin and lower back pain. Imaging studies showed progression of disease with an L4 vertebral compression fracture. Peripheral blood flow cytometry at this time was immunophenotypically consistent with MCL; the neoplastic cells accounted for 13.9% of analyzed cells and coexpressed CD19, CD20, CD22, CD5 (dim), FMC7, CD81, and SOX11, and were negative for CD10, CD23, CD11c, CD25, and CD103. A CCND1::IGH rearrangement was identified by FISH, further confirming the diagnosis.

The patient underwent biopsy of the L4 vertebral fracture site (Fig. 1). Sections showed fragments of trabecular bone with extensive bone marrow infiltration by a diffuse, polymorphous infiltrate of foamy histiocytes, small lymphocytes, eosinophils, and scattered large/atypical cells with irregular nuclear contours, prominent nucleoli, and moderate cytoplasm reminiscent of RS cells; these atypical cells accounted for approximately 10% of overall cellularity. Multifocal necrosis was also seen. Both small and large neoplastic cells were positive for CD45, CD20, CD19, PAX-5, CD79a, OCT2, CD30, cyclin D1, cMyc, and p53, as well as EBV (EBER in situ hybridization). LMP1 was positive in a subset of the large cells. All neoplastic cells were negative for SOX11, CD3, CD5, CD15, S100, CD1a, Langerin, CD68, CD163, and cytokeratin. FISH studies were performed, revealing presence of CCND1::IGH gene rearrangement. A diagnosis of MCL was rendered, with a note that the findings were reminiscent of “EBV-associated high-grade transformation of MCL.” EBV was subsequently identified in the previously submitted peripheral blood sample by PCR. Based on this diagnosis, patient was treated with two cycles of R-DHAX.

Two months later, the patient developed progression of disease. PET/CT scanning revealed multifocal lymphadenopathy above and below the diaphragm, prompting an axillary node biopsy (Fig. 2). Sections from the lymph node showed a diffuse proliferation of medium to large-sized atypical lymphoid cells with irregular nuclear contours, vesicular chromatin, prominent nucleoli, and moderate amounts of amphophilic cytoplasm. Karyorrhexis and mitotic activity were prominent. Focal areas of necrosis were seen. Occasional scattered Hodgkin/RS-like cells were seen in the background of neoplastic atypical cells. The atypical lymphoid cells accounted for approximately 20% of overall cellularity and were positive for CD2, CD3 (weak), CD8, perforin, granzyme, TIA-1, CD56 (subset), PDL1, LMP1, cMYC (subset), MUM1, CD38, TCRβ (subset), and EBV (EBER in situ hybridization). Proliferation rate, estimated using Ki-67, was ∼50–60% in neoplastic cells. Neoplastic cells were negative for cyclin D1, SOX11, CD5, CD7, CD4, TCRδ, ICOS, PD1, CD94, CD30, CD15, CD19, CD20, PAX-5, and OCT2. Admixed RS-like cells were positive for EBER, cyclin D1, CD30, and PAX-5 (dim), but negative for CD15 and T-cell markers. Admixed small lymphocytes were CD3-positive T cells co-expressing pan-T-cell antigens (mix of CD4 and CD8 positive cells). Virtually no small B cells were identified by multiple B-cell markers. A diagnosis of peripheral T-cell lymphoma, EBV-positive was rendered according to WHO, Revised 4th Edition criteria (EBV-positive nodal T-cell and NK-cell lymphoma by WHO, 5th Edition criteria).

Additional FISH studies performed on the lymph node specimen demonstrated presence of CCND1::IGH, similar to that in peripheral blood and bone biopsy specimens. We further performed PCR based molecular clonality studies on all three specimens to interrogate clonal relatedness (Fig. 3). Peripheral blood testing was performed on an archived cell pellet; testing of the two tissue specimens was performed on formalin-fixed, paraffin-embedded tissue. Immunoglobulin (IGH and IGK) clonality testing demonstrated conserved monoclonal peaks for both IGH and IGK in all three samples. TCRγ clonality testing showed a distinct monoclonal peak in the lymph node specimen only.

NGS-based molecular genetic studies (B CAPP-Seq panel) were performed on all three samples (Fig. 4; Table 1). Library preparation was done using the Roche KAPA kit and sequencing was done in NextSeq. We identified 12 mutations that were shared between all three samples. Of note, 11 of these were in the IGLL5 gene, a frequent target of somatic hypermutations that can involve the intronic regions; it is therefore expected that a B-cell neoplasm would have many mutations in this gene and that those mutations would be conserved in clonally related relapses of that neoplasm. An additional 7 mutations were shared by the L4 vertebra B-cell lymphoma and the lymph node T-cell lymphoma, suggesting a closer clonal relationship between those two samples than with the peripheral blood. Among these 7 mutations were 2 variants of unknown significance within the CCND1 gene. Although 4 mutations were shared between the peripheral blood and the bone biopsy, but not the lymph node, these were interpreted as mutations unique to the peripheral blood, with peripheral blood contamination of the bone biopsy specimen. These mutations findings support a model in which an early ancestral B-cell precursor gave rise to three clonally related tumors through a series of divergent evolution. Although VAFs for each of the three samples are somewhat lower than expected for the estimated cellularity based on immunohistochemistry and flow cytometry, this might be partially explainable by variations in sampling between the areas used to estimate cellularity and what was submitted for genetic testing.

The patient underwent 6 total cycles of CHOEP, receiving pembrolizumab as well during the last two cycles. He then underwent autologous stem cell transplant; however, new hypermetabolic lymph nodes were detected 3 months later. Treatment with GELOX was attempted, but the patient passed away during the second cycle.

This case constituted a diagnostic challenge. The differential diagnosis for the bone biopsy included classic Hodgkin lymphoma, given the abundance of Reed-Hodgkin-like cells. However, many small B-lymphocytes positive for CD5, cyclin D1, and EBER were also present. Due to the spectrum of cell sizes and morphologies sharing cyclin D1 and EBER expression, as well as the established history of MCL, we favored classification as a transformation of MCL to a more aggressive histological type, rather than invoking classic Hodgkin lymphoma.

Progression of MCL from an indolent form to a more aggressive form with high-grade histology has been described [6]. In general, the histologic subtype of mantle zone lymphoma is known to vary across sequential biopsies in the same patient. In one study of 47 patients, a shift in histologic type between biopsies was observed in 28% of cases [7]. Interestingly, shifts occurred bidirectionally, with classical or small-cell morphology shifting to blastoid in eight of 36 cases, while shifts from blastoid to classical or small-cell morphology occurred in five of ten cases; these shifts toward more indolent-appearing morphology were attributed to therapeutic effect.

The immunophenotype of the neoplastic cells in the axillary lymph node biopsy is consistent with T-cell lineage, and this is further supported by the presence of a monoclonal TCRγ rearrangement. However, the presence of a CCND1::IGH rearrangement, as well as the conservation of IGH and IGK clonal peaks across all three samples, demonstrate that the T-cell lymphoma is clonally related to the prior B-cell lymphoma. The NGS data support this and further suggest a sequential progression of disease, with the bone and lymph node lymphoma cells having a more recent common progenitor than the cells identified in the peripheral blood. The findings are therefore consistent with true lineage switch from a mature B-cell lymphoma to a T-cell lymphoma.

True switch from B-lineage to T-lineage differentiation in human neoplasms have been reported only rarely in the literature. Downregulation of B-lineage markers and emergence of T-lineage or histiocytic markers with preserved immunoglobulin gene rearrangement was recently reported in a patient in the context of CAR-T-cell therapy [8]. These changes, associated with CAR-T resistance, are proposed to be a consequence of genetic remodeling due to newly acquired mutations, as well as increased methylation and consequential silencing of B-lineage genes. In our patient, the reason for lineage switch is unclear. Although there were mutations unique to the T-cell lymphoma sample, none of the identified mutations are likely to have played a direct role in lineage switch.

One older example of lineage switch between B-cell and T-cell lymphoma phenotype was reported in 1992, in which a histologically indolent T-cell lymphoma relapsed as a cutaneous B-cell lymphoma, followed by a histologically distinct T-cell lymphoma. Conserved chromosomal abnormalities, as well as similar monoclonal TCRγ rearrangements, were used to support the claim of lineage switch, as opposed to sequential presentations of clonally distinct lymphomas [9].

The presence of EBV infection in this case is of great interest. MCL with Epstein-Barr virus is rare but has been reported, occurring in 5% of 138 cases in one study [10]. EBV-positive cases were associated with greater frequency of anemia, increased LDH levels, and higher MCL international prognostic index groups (MIPI), though no significant difference was observed for Ann Arbor stage or other tested clinical metrics. Cases of MCL relapsing with RS-like cells and EBV positivity have also been reported previously, including one case in the post-stem cell transplant setting [5, 11].

In this case, the patient’s original mantle zone lymphoma diagnosis was made many years prior to his presentation at our institution, so the diagnostic sample was not available to us for confirmatory testing. We therefore do not know whether EBV infection was present at initial diagnosis. Given the rarity of both EBV-associated MCL and mantle cell evolution to T-cell lymphoma, the possibility that EBV infection in some way contributed mechanistically to the lineage switch event must be considered. The EBV non-transcriptional RNA EBER2 is known to interact with PAX-5 to recruit PAX-5 to the terminal repeats of the EBV genome [12]. It has also been shown that depletion of PAX-5 in EBV-infected B cells results in activation of certain EBV-associated proteins, such as LMP1 and LMP2 [13]. However, a direct connection between EBV and lineage switch has not been established.

The mechanism by which lineage switch from B-cell lineage to other lineages occurs remains unclear. Multiple models exist to explain the switch [14]. In the dedifferentitation-redifferentiation model, the primary neoplasm reverts to a more immature, pluripotent state and then matures into a lineage different from that of the primary neoplasm [15]. In the common progenitor model, a single pluripotent progenitor gives rise to both the earlier and later neoplasms of different lineages, such that both share certain genetic mutations or other abnormalities without one being directly descended from the other (conceptually, a “sibling” relationship rather than a “parent-child” relationship) [16]. Finally, in the transdifferentiation model, one mature neoplasm of a given lineage develops directly into a second mature neoplasm of a different lineage, without first regressing to a more immature, pluripotent state [17].

In our case, we favor the transdifferentiation model. If the T-cell and B-cell lymphomas each diverged from a single progenitor, the T-cell lymphoma would not be expected to harbor IGH and IGK rearrangements, which are features specific to B-cell lineage and would not be present in the hypothetical progenitor. The dedifferentiation-redifferentiation model is harder to disprove; however, there is no evidence of any immature or undifferentiated intermediary between the two neoplasms in either sample. Similar reasoning can be applied to the cases of lineage switch from B-cell neoplasms to histiocytic neoplasms that have been reported in the literature [14]. PAX-5 (paired box gene 5) is an important gene in the development and maintenance of the B-cell phenotype. Selected deletion of PAX-5 in the mature B cells of mice has been shown to allow dedifferentiation of the B cells, followed by redifferentiation into T cells, without loss of immunoglobulin rearrangement [18]. Mice injected with PAX-5 deleted B cells developed aggressive lymphomas of “progenitor” type. However, it is not clear that mutation or deletion of PAX-5 is necessary for lineage switch from B cell to another lineage in vivo. A small study of 2 cases of B-cell lymphoma with lineage switch to histiocytic sarcoma did not reveal mutations in the PAX-5 gene in either case [19].

The loss of BCL1 expression between the bone marrow biopsy and the lymph node biopsy is of interest, particularly given the preservation of the CCND1::IGH fusion in the lymph node biopsy. BCL1 is overexpressed in MCL because the CCND1 gene is fused to the IGH promoter [20]. Because IGH is constitutively expressed in normal mature B cells, the fusion leads to dysregulated, constitutive expression of BCL1. Presumably, the shift to T-cell phenotype would deactivate the IGH promoter, reducing BCL1-expression levels, thereby explaining the immunohistochemical findings. Although new mutations in CCND1 could potentially affect the epitope bound by the anti-BCL1 antibody in the immunohistochemical process, leading to false-negative results, the two variants of undetermined significance identified in the CCND1 gene were present in both the lymph node and bone biopsies, making this second possible explanation less likely.

In summary, we present a very rare case of lineage switch from MCL to an EBV-positive, T-cell lymphoma with an intermediating high-grade B-cell lymphoma with Reed-Hodgkin-like cells. All three samples were positive for CCND1::IGH fusion and identical monoclonal IGH/IGK transcript lengths. The latter two samples shared seven somatic mutations not detected in the first sample, suggesting a progression through the samples. Thorough evaluation and consistent reporting of such unusual examples of lineage switch will be necessary to further develop our understanding of this rare phenomenon.

We thank the staff at the Hematopathology and Molecular laboratories at the Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, for their contribution during the data collection for this case report.

Written informed consent was obtained from the patient for publication of the details of their medical case and any accompanying images. Only deidentified data were used in this manuscript, and no information revealing the patient’s identity was included. The New York Presbyterian Hospital/Weill Cornell Medicine is in compliance with the CARE guidelines for case reports. This study protocol was reviewed and approved by the Weill Cornell Medicine Institutional Review Board (WCM-IRB) at Weill Cornell Medical College of Cornell University, Approval No. 0107004999.

The authors have no conflicts of interest to declare.

This study was not supported by any sponsor or funder.

All authors reviewed the manuscript prior to publication. Dr. Paul Barone and Dr. Madhu Ouseph were primarily responsible for writing and editing the text of the manuscript itself. Dr. Wayne Tam oversaw the molecular testing and provided interpretation of the test results. Dr. Julia Geyer was the primary pathologist for a subset of the specimens included in the article and served as a consultant for the descriptions provided of those specimens. Dr. John Leonard and Dr. Adrienne Phillips provided information related to the patient’s clinical course.

The data that support the findings of this study are not publicly available due to their containing information that could compromise the privacy of the patient, but are available from the corresponding author, P.B. ([email protected]), upon reasonable request.