First reported case of BRAF V600E mutation in T-cell prolymphocytic leukaemia

We report here the first identified case of T-cell prolymphocytic leukaemia (T-PLL) with BRAF V600E mutation. T-PLL is an extremely rare and aggressive neoplasm of mature T cells. Presenting with high leukocyte counts, lymphadenopathy, splenomegaly, hepatomegaly, skin lesions, pleuroperitoneal effusions and/or central nervous system (CNS) involvement, T-PLL is often chemorefractory.¹ Prognosis after failure of first-line treatment with alemtuzumab is very poor despite utilization of agents such as fludarabine, mitoxantrone and cyclophosphamide (FMC) and bendamustine.² Autologous or allogeneic transplantation are commonly used for the treatment of relapsed and/or refractory disease.³ New data regarding use of more targeted therapies, such as venetoclax, are emerging.³ Identification of novel mutations, such as BRAF V600E described here, offers promising new therapeutic targets for this challenging disease.

Several molecular mutational studies and drug sensitivities in T-PLL have previously been reported.^1,4,5 Andersson et al.¹ utilized ex vivo drug testing and mutation profiling to identify cyclin-dependent kinase inhibitors, HDAC inhibitors, JAK inhibitors, and PI3K inhibitors as potentially efficacious drugs. These novel therapies, while used for other diagnoses, have not been thoroughly tested in vivo for T-PLL patients. The drugs which showed the highest T-PLL-specific response were the BCL2 inhibitors navitoclax and venetoclax. Notably, Boidol et al.³ reported two patients with highly refractory TPLL with positive treatment responses to venetoclax.

The BRAF V600E mutation is a targetable mutation found in many cancers: thyroid, colorectal, melanoma, sarcoma, lung, and hairy cell leukaemia.⁶ BRAF V600E targeting drugs are a mainstay in the treatment of many of these malignancies. To our knowledge, there has been no report of this mutation in T-PLL. Of note, mouse studies have shown that combinatorial therapy involving dasatinib, a tyrosine kinase inhibitor, sensitizes cancer cells against the BRAF V600E mutations.⁷

A 54-year-old male presented to his primary-care provider in early January 2018 and was found to have an elevated white blood cell (WBC) count of 40 cells/μl. Computed tomography (CT) of chest/abdomen/pelvis (C/A/P) showed multiple lymph nodes above and below the diaphragm. WBC count remained in the range of 30s cells/μl until October 2018 with an increase to 113 cells/μl. Symptomatically, the patient reported abdominal bloating, nausea, headache, unintentional weight loss of 20 lbs (9 kg), lower extremity bruising and was found to be jaundiced. He was admitted with notable labs: WBC of 1136 cells/µl, haemoglobin (Hb) of 115 g/l, platelet count of 26 × 10³, total bilirubin of 104 mg/l and direct bilirubin of 651 mg/l. The patient was transferred to our institution for further evaluation.

Further analyses were performed on arrival at our institution. Peripheral blood and bone marrow were extensively involved by an abnormal T-cell proliferation, characterized as small to medium-sized cells with irregular to notched nuclei, mature chromatin, small nucleolus, and conspicuous cytoplasmic protrusions (Fig 1A, B). Flow cytometry identified an abnormal T-cell population positive for cluster of differentiation (CD) 2, CD3 (surface), CD4, CD5, CD7, CD26, CD52, and negative for CD25, CD56 and terminal deoxynucleotidyl transferase (TdT). Immunohistochemistry additionally demonstrated T-cell lymphoma (TCL)-1 expression (Fig 1C), with negative CD30, T-cell intracellular antigen (TIA)-1 and granzyme B. Polymerase chain reaction (PCR) confirmed clonal T-cell gamma gene rearrangements. Karyotype was complex: 46 ∼ 47,XY,add(2)(p13),add(2)(q11.2),−6, i(8)(q10),del(9)(p21),del(11)(q13q23),der(12)t(2;12)(q13;p11.2), −13,inv(14)(q11.2q32),−17,−18,add(19)(q13.1),−20,add(21)(p11.2), +r,+3 ∼ 4mar[cp8]/46,XY[12]. T-PLL dx confirmed.

Fig 1.

BRAF V600E-mutated T-prolymphocytic leukaemia. (A) Peripheral blood (Wright Giemsa ×600, inset ×1000).(B–D) Bone marrow core (B, haematoxylin–eosin, ×200) with immunohistochemistry demonstrating cluster of differentiation (CD) 3 (C, ×100) and TCL1 (D, ×100) expression. (E–G) Paraspinal mass core biopsy (E, haematoxylin–eosin, ×200) with immunohistochemistry positive for CD3 (F, ×100) and BRAF V600E (G, ×100). (H) Differential melt curves to detect BRAF 600E mutation; BRAF V600 alleles 49°C (normal control); BRAF 600E alleles 55°C (positive control). Peak melt temperature from patient DNA is 55°C. No Template Control (NTC) controls for polymerase chain reaction contamination.

The patient had a challenging clinical course. On presentation, he had normal renal function but liver functions tests (LFTs) were elevated (total bilirubin of 160 mg/l, direct bilirubin of 123 mg/l). Abdominal ultrasound revealed hepatomegaly and splenomegaly (17 cm) with moderate ascites but did not reveal any evidence of obstruction. Paracentesis revealed malignant ascites with leukaemic involvement. Given the patient’s significant symptoms, he received induction therapy with FMC with haematologic response. Subsequently, he was transitioned to alemtuzumab consolidation and completed 11 weeks of therapy with sustained haematologic response. However, progressive disease was noted with increased lymphadenopathy on positron emission tomography/computed tomography (PET-CT) and CT scans. Left inguinal node and bone marrow biopsies confirmed disease involvement. Molecular evaluation by next generation sequencing (FoundationOne Heme panel) on the lymph node tissue demonstrated BRAF V600E, ATM D2721N, CDKN2A/B loss, RAD50 Y625, STAT5B N642H and TCL1A rearrangement. The patient was started on salvage NECTAR (nelarabine, cyclophosphamide and etoposide) therapy with the goal of subsequent allogeneic bone marrow transplant.⁸ Intrathecal (IT) chemotherapy confirmed CNS involvement and the patient received 3×/weekly IT chemotherapy. After two cycles of NECTAR, haematologic response was noted but PET-CT demonstrated worsening lymphadenopathy and a new left-paraspinous mass. Biopsy of the paraspinal mass confirmed T-PLL (Fig 1D, E). Notably, BRAF V600E mutation was again detected, this time by immunohistochemistry as well as by PCR and melt curve analysis (Fig 1F, G). Given these findings, the patient was started on dasatinib (for a total duration of five weeks) pending venetoclax authorization with subsequent transition and inpatient dose escalation. Unfortunately, 10 days after venetoclax initiation, the patient was admitted with neutropaenic fever and tumour lysis syndrome (TLS), requiring a hold on his therapy. Vemurafenib, an FDA-approved BRAF V600E inhibitor,⁹ was initiated based on the molecular results, at a dose of 960 mg PO Q12. Receiving a total of 20 days of therapy, the patient had improvement in renal function and WBC count. However, his respiratory and volume status continued to worsen and the patient unfortunately expired (Fig. 2).

Fig 2.

Haemoglobin, creatinine, and white blood cell count during vemurafenib therapy (20 days). The patient’s haemoglobin (Hb), creatinine (Cr), and white blood cell (WBC) count during therapy with vemurafenib, an FDA-approved BRAF V600E inhibitor.

Treatment of T-PLL is challenging with few, well-defined choices; new targeted therapies show promise for even highly refractory and advanced disease. In this paper, we report the first known BRAF V600E mutation found in T-PLL. Previous studies have shown recurrent mutations in the JAK/STAT pathway, ATM, genetic modifiers and DNA repair mechanisms; this BRAF V600E mutation likely represents an uncommon finding but more studies are required to identify other such mutations with potential therapeutic benefit.^10–15 Our patient, having progressed through standard of care treatments, was trialled on novel treatments including dasatinib, venetoclax and vemurafenib. In the setting of advanced disease, vemurafenib therapy showed some promise in our patient before he ultimately expired due to other complications. Further clinical experience will be required in order to determine the efficacy and role of novel therapies, including BRAF targeting drugs, in the treatment of T-PLL.