Novel BRAF N581S mutation in mantle cell lymphoma

Abstract BRAF mutations are associated with a small number of hematologic malignancies, including hairy cell leukemia and histiocytic disorders. In addition, BRAF mutations have also been detected in low frequency in other B‐cell lymphomas, such as chronic lymphocytic leukemia and diffuse large B‐cell lymphoma, but never in mantle cell lymphoma (MCL). We present a case of a 69‐year‐old female with classic MCL harboring a BRAFN581S mutation. To our knowledge, this is the first reported case of any BRAF mutation in MCL.


INTRODUCTION
BRAF is a serine/threonine kinase and a component of the mitogenactivated protein kinase (MAPK) pathway [1].Mutations in BRAF lead to an oncogenic form of the protein causing constitutive activation of the MAPK pathway and dysregulated cell proliferation [2].BRAF V600E   is the most common mutational variant and is frequently associated with solid tumors, such as melanoma, thyroid, and colorectal cancers [2].In the realm of hematologic malignancies, BRAF V600E   is strongly implicated as a driver mutation in the development of hairy cell leukemia (HCL) and systemic histiocytic disorders such as Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD) [3,4].However, while BRAF mutations have been described in other hematologic malignancies, including diffuse large B-cell lymphoma (DLBCL), they are rare outside of HCL and histiocytic disorders [4].
Additionally, the clinical significance of mutational variants outside of V600E is also unclear.We herein present a case of a 69-year-old female with classic MCL, found to have a BRAF N581S mutation.To the best of our knowledge, this is the first case of a BRAF mutation being reported in a patient with MCL.

CASE
We describe the case of a 69-year-old female with a history of colon polyps, pancreatic cyst, osteopenia, and MCL.She was referred to Hematology after being found to have asymptomatic leukocytosis, with an elevated white blood cell count of 25,200/mm 3 (normal range: 4000-11,000/mm 3 ) and an absolute lymphocyte count of 20,900/mm 3 (normal range: 800-31,000/mm 3 ) (Figure 1A).Her hemoglobin and platelet count were within the normal range.Peripheral blood flow cytometry revealed lambda-restricted monotypic B cells that were negative for CD5, CD10, and CD23.
The patient subsequently underwent a bone marrow (BM) biopsy.
The BM aspirate showed increased small to medium-sized atypical lymphoid cells (Figure 1B).Flow cytometry of the BM showed 48% CD5(-)/CD10(-) kappa-restricted monotypic B cells.Hematoxylin and eosin of the BM core biopsy demonstrated increased interstitial infiltrate of small to medium-sized atypical lymphoid cells (Figure 1C) that were positive for CD79a (Figure 1D), but were negative for CD5 (Figure 1E) in comparison to CD3 (inlet, Figure 1F).While these cells were positive for BCL1 (Figure 1G), they were negative for SOX11 (inlet, Figure 1H).
Conventional karyotyping demonstrated the presence of two clones   1I,J).
Because the patient was asymptomatic and without cytopenias, lymphadenopathy, and splenomegaly, the decision was made to place her on watch and wait surveillance.She continues to be monitored 32 months after her initial diagnosis without indications for treatment initiation.

DISCUSSION
We describe a unique case of classic MCL with the following fea-  [6,7].
However, unlike HCL and the systemic histiocytoses where the high frequency of BRAF mutations suggests that BRAF serves as an oncogenic driver, in other hematologic malignancies, it is unclear whether BRAF plays a role in disease pathogenesis, or if it is an incidentally noted passenger mutation.For example, one study examined in vitro response of BRAF-mutated CLL cells to both sorafenib and PLX4720, an analog of vemurafenib.While cell death was induced by sorafenib in the BRAF-mutated CLL cells, there was no significant effect from PLX4720 on the cells, suggesting that the clinical significance of BRAF mutations outside of HCL and histiocytic disorders requires further investigation [7].Another study noted that of 642 CLL patients, 4.5% harbored a BRAF V600E mutation and appeared to have shorter survival, required more treatment, and were seen more commonly in patients with Richter transformation [8].BRAF mutations were also seen more commonly in IGHV unmutated patients, which are typically associated with worse clinical outcomes [9].Given that leukemic non-nodal MCL patients share a similar cell of origin in memory B cells as CLL patients, this raises the question of whether BRAF mutations may portend the same poorer prognosis in MCL patients as well.Our patient had an indolent disease course despite the presence of a BRAF mutation, which may be related to her IGHV somatic hypermutation, as this has been associated with a less aggressive disease course in MCL [10].
Furthermore, while V600E mutation is the most common BRAF mutation, the N581S variant found in our patient is rare.N581S has been reported in a various tumors including melanoma, sarcoma, colorectal, ovarian, and lung cancers [11].An N581I variant has also been described in marginal zone lymphoma [6].This amino acid substitution is found in exon 15 in the BRAF kinase domain, but its effect on kinase activity is uncertain, though there is some suggestion in case reports that the N581S mutation may portend decreased sensitivity to BRAF inhibition [12].
BRAF V600E inhibition has made significant progress for patients with certain solid tumors, but has not been extensively studied as a treatment for hematologic malignancies.In HCL, BRAF inhibition for patients with relapsed and refractory disease can yield a high overall response rate (ORR) of 96%-100% [13].In systemic histiocytoses, first-line treatment with vemurafenib had an ORR of 61.5% [14].BRAF inhibition has not been studied extensively in other lymphoid malignancies.MCL is an aggressive lymphoma with variable prognosis.For young, fit patients, standard treatment consists of cytarabine-based chemoimmunotherapy, followed by autologous stem cell transplant and rituximab maintenance.This can lead to long remissions, but is not curative.For elderly or unfit patients, front-line chemoimmunotherapy with bendamustine-rituximab is standard, but has shorter remissions.In the relapsed setting, Bruton tyrosine kinase inhibitors are standard but lead to responses lasting between only 1 and 2 years [15].
The reported case here is notable for several reasons.First, this is the first described case of any BRAF mutation in MCL, and second, the first described case of BRAF N581S mutation in NHL in the English literature.To the best of our knowledge, NHLs have never been

eJHaem. 2024; 5 :F I G U R E 1
247-250.wileyonlinelibrary.com/journal/jha2247 Composite microphotographs of a mantle cell lymphoma involving bone marrow (A-H) and colon (I and J).Frequent atypical small mature lymphoid cells are present in the peripheral blood (A, Wright-Giemsa, original magnification 1000×) and bone marrow aspirate (B, Wright-Giemsa, 1000×).The atypical lymphoid cells exhibit interstitial infiltrate of bone marrow and account for ∼50% of total cellularity (C, hematoxylin and eosin [H&E], 400×) and are positive for CD79a (D, 200×).In comparison to CD3 (E, 200×), the atypical B cells are negative for CD5 (F, inlet, 200×), but positive for BCL1 (G, 400×) albeit negative for SOX11 (H, inlet, 400×).The atypical lymphoid cells show mantle zone growth around a reactive secondary germinal center (I, 200×) and in the lamina propria of the colon and are positive for BCL1 (J, 200× treated with BRAF inhibitors.If additional reports of BRAF mutations in MCL emerge in the literature, then BRAF inhibition could represent a potential new treatment target.AUTHOR CONTRIBUTIONS Nisha Hariharan and Benjamin M. Heyman conceived the idea for work and wrote the manuscript.Davsheen Bedi, Huan-You Wang, and Michael Y. Choi analyzed the data and assisted with manuscript writing.