Phospho-ERK(THR202/Tyr214) is overexpressed in hairy cell leukemia and is a useful diagnostic marker in bone marrow trephine sections

Long-term outcomes in patients with relapsed or refractory hairy cell leukemia treated with vemurafenib monotherapy

Vemurafenib, an oral BRAF inhibitor, has demonstrated high response rates in relapsed/refractory (R/R) hairy cell leukemia (HCL). However, little is known about long-term outcomes and response to retreatment. Herein, we report the results of 36 patients with R/R HCL treated with vemurafenib from the United States arm of the phase 2 clinical trial (NCT01711632). The best overall response rate was 86%, including 33% complete response (CR) and 53% partial response (PR). After a median follow-up of 40 months, 21 of 31 responders (68%) experienced relapse with a median relapse-free survival (RFS) of 19 months (range, 12.5-53.9 months). There was no significant difference in the RFS for patients with CR vs PR. Fourteen of 21 (67%) relapsed patients were retreated with vemurafenib, with 86% achieving complete hematologic response. Two patients acquired resistance to vemurafenib with the emergence of new KRAS and CDKN2A mutations, respectively. Six of 12 (50%) responders to vemurafenib retreatment experienced another relapse with a median RFS of 12.7 months. Overall survival (OS) was 82% at 4 years, with a significantly shorter OS in patients who relapsed within 1 year of initial treatment with vemurafenib. Higher cumulative doses or a longer duration of treatment did not lengthen the durability of response. All adverse events in the retreatment cohort were grade 1/2 except for 1 case of a grade 3 rash and 1 grade 3 fever/pneumonia. Our data suggest that vemurafenib retreatment is a safe and effective option for patients with R/R HCL.

Chronic Myelomonocytic Leukemia With Fibrosis Is a Distinct Disease Subset With Myeloproliferative Features and Frequent JAK2 p.V617F Mutations

A subset of patients with chronic myelomonocytic leukemia (CMML) presents with significance myelofibrosis. In myelodysplastic syndromes, significant myelofibrosis has been associated with adverse outcomes and p53 dysregulation. However, in CMML the clinical and molecular correlates of significant myelofibrosis at presentation remain poorly understood. From a cohort of 651 CMML patients, we identified retrospectively 20 (3.1%) cases with moderate to severe reticulin fibrosis (CMML-F) detected at diagnosis, and we compared them to CMML patients without fibrosis (n=631) seen during the same period. Patients with CMML-F had a median age of 69.8 years (range, 24.8 to 91.2 y) and most (13; 65%) were men. Patients with CMML-F differed significantly from other CMML patients across the following parameters: white blood count, absolute monocyte count, serum lactate dehydrogenase level, splenomegaly, and bone marrow blast percentage. Notably, the frequency of JAK2 p.V617F mutation was higher in CMML-F patients compared with other CMML patients (P<0.001). Most CMML-F patients (12/20; 60%) had myeloproliferative CMML. Dysregulation of p53 was uncommon in CMML-F. CMML-F patients tended to have a shorter median overall survival compared with other CMML patients (P=0.079). Multivariate analysis using the Cox proportional hazards model showed an independent association between CMML-F and overall survival (P=0.047). In summary, unlike typical CMML, CMML-F is commonly associated with JAK2 p.V617F. The high frequency of myeloproliferative features and JAK2 p.V617F mutation, and the low frequency of p53 dysregulation, suggest that fibrosis in the context of CMML has a different pathogenesis from that previously reported in myelodysplastic syndrome.

Mutations in the RAS-BRAF-MAPK-ERK pathway define a specific subgroup of patients with adverse clinical features and provide new therapeutic options in chronic lymphocytic leukemia

Mutations in genes of the RAS-BRAF-MAPK-ERK pathway have not been fully explored in patients with chronic lymphocytic leukemia. We, therefore, analyzed the clinical and biological characteristics of chronic lymphocytic leukemia patients with mutations in this pathway and investigated the in vitro response of primary cells to BRAF and ERK inhibitors. Putative damaging mutations were found in 25 of 452 patients (5.5%). Among these, BRAF was mutated in nine patients (2.0%), genes upstream of BRAF (KITLG, KIT, PTPN11, GNB1, KRAS and NRAS) were mutated in 12 patients (2.6%), and genes downstream of BRAF (MAPK2K1, MAPK2K2, and MAPK1) were mutated in five patients (1.1%). The most frequent mutations were missense, subclonal and mutually exclusive. Patients with these mutations more frequently had increased lactate dehydrogenase levels, high expression of ZAP-70, CD49d, CD38, trisomy 12 and unmutated immunoglobulin heavy-chain variable region genes and had a worse 5-year time to first treatment (hazard ratio 1.8, P=0.025). Gene expression analysis showed upregulation of genes of the MAPK pathway in the group carrying RAS-BRAF-MAPK-ERK pathway mutations. The BRAF inhibitors vemurafenib and dabrafenib were not able to inhibit phosphorylation of ERK, the downstream effector of the pathway, in primary cells. In contrast, ulixertinib, a pan-ERK inhibitor, decreased phospho-ERK levels. In conclusion, although larger series of patients are needed to corroborate these findings, our results suggest that the RAS-BRAF-MAPK-ERK pathway is one of the core cellular processes affected by novel mutations in chronic lymphocytic leukemia, is associated with adverse clinical features and could be pharmacologically inhibited.

Frequent BRAF V600E and Absence of TERT Promoter Mutations Characterize Sporadic Pediatric Papillary Thyroid Carcinomas in Japan

Pediatric papillary thyroid carcinoma (PTC) has unique features but requires further genetic investigation. Moreover, there has been increasing concern about the risk for pediatric PTC in Japan after the Fukushima accident. This study aims to evaluate the frequencies of BRAF and TERT promoter mutations and to examine their significance in non-radiation-associated pediatric PTCs in Japan. We enrolled 81 pediatric PTC patients aged ≤20 years. The control group included 91 adult PTCs from patients >20 years old. BRAF and TERT mutations were analyzed by allele-specific-PCR and/or Sanger sequencing. Compared with adult PTCs, pediatric PTCs exhibited larger tumor size, more frequent lymph node metastasis, and less classical histology. The prevalence of BRAF ^V600E in pediatric PTCs was 54% and significantly lower than that in adults of 85%. In the pediatric PTCs, BRAF ^V600E was positively associated with older age, classical histology, and the lymph node metastasis but independent from other clinicopathological factors. TERT mutations were identified in 13% of adults and in none of the pediatric PTCs. In conclusion, pediatric PTCs are characterized by more advanced clinicopathological features, lower BRAF ^V600E frequency, and absence of TERT mutation. The BRAF ^V600E frequency in this study is similar to the reported BRAF ^V600E frequency in the ultrasonographically screened pediatric PTCs in Fukushima.

Genomics of Hairy Cell Leukemia

Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the discovery of its underlying genetic cause, the BRAF-V600E kinase-activating mutation, which is somatically and clonally present in almost all patients through the entire disease spectrum and clinical course. By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior. Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis. Conversely, BRAF-V600E is absent in other B-cell neoplasms, including mimickers of HCL that require different treatments (eg, HCL-variant and splenic marginal zone lymphoma). Thus, testing for BRAF-V600E allows for a genetics-based differential diagnosis between HCL and HCL-like tumors, even noninvasively in routine blood samples. BRAF-V600E also represents a new therapeutic target. Patients' leukemic cells exposed ex vivo to BRAF inhibitors are spoiled of their HCL identity and then undergo apoptosis. In clinical trials of patients with HCL who have experienced multiple relapses after purine analogs or who are refractory to purine analogs, a short course of the oral BRAF inhibitor vemurafenib produced an almost 100% response rate, including complete remission rates of 35% to 42%, without myelotoxicity. To further improve on these results, it will be important to clarify the mechanisms of incomplete leukemic cell eradication by vemurafenib and to explore chemotherapy-free combinations of a BRAF inhibitor with other targeted agents (eg, a MEK inhibitor and/or an anti-CD20 monoclonal antibody).

BRAF V600E mutation in hairy cell leukemia: from bench to bedside

Hairy cell leukemia (HCL) is a distinct clinicopathological entity whose underlying genetic lesion has remained a mystery for over half a century. The BRAF V600E mutation is now recognized as the causal genetic event of HCL because it is somatic, present in the entire tumor clone, detectable in almost all cases at diagnosis (encompassing the whole disease spectrum), and stable at relapse. BRAF V600E leads to the constitutive activation of the RAF-MEK-extracellular signal-regulated kinase (ERK) signaling pathway which represents the key event in the molecular pathogenesis of HCL. KLF2 and CDNK1B (p27) mutations may cooperate with BRAF V600E in promoting leukemic transformation. Sensitive molecular assays for detecting BRAF V600E allow HCL (highly responsive to purine analogs) to be better distinguished from HCL-like disorders, which are treated differently. In vitro preclinical studies on purified HCL cells proved that BRAF and MEK inhibitors can induce marked dephosphorylation of MEK/ERK, silencing of RAF-MEK-ERK pathway transcriptional output, loss of the HCL-specific gene expression profile signature, change of morphology from “hairy” to “smooth,” and eventually apoptosis. The overall response rate of refractory/relapsed HCL patients to the BRAF inhibitor vemurafenib approached 100%, with 35% to 40% complete remissions (CRs). The median relapse free-survival was about 19 months in patients who had achieved CR and 6 months in those who had obtained a partial response. Future therapeutic perspectives include: (1) combining BRAF inhibitors with MEK inhibitors or immunotherapy (anti-CD20 monoclonal antibody) to increase the percentage of CRs and (2) better understanding of the molecular mechanisms underlying resistance of HCL cells to BRAF inhibitors.

Potential role of AKT/mTOR signalling proteins in hairy cell leukaemia: association with BRAF/ERK activation and clinical outcome

The potential role of AKT/mTOR signalling proteins and its association with the Raf-MEK-ERK pathway was investigated in hairy cell leukaemia (HCL). BRAFV600E expression and activated forms of AKT, mTOR, ERK1/2, p70S6k and 4E-BP1 were immunohistochemically assessed in 77 BM biopsies of HCL patients and correlated with clinicopathological and BM microvascular characteristics, as well as with c-Caspase-3 levels in hairy cells. Additionally, we tested rapamycin treatment response of BONNA-12 wild-type cells or transfected with BRAFV600E. Most HCL cases expressed p-p70S6K and p-4E-BP1 but not p-mTOR, being accompanied by p-ERK1/2 and p-AKT. AKT/mTOR activation was evident in BONNA-12 cells irrespective of the presence of BRAFV600E mutation and was implicated in cell proliferation enhancement. In multivariate analysis p-AKT/p-mTOR/p-4E-BP1 overexpression was an adverse prognostic factor for time to next treatment conferring earlier relapse. When p-AKT, p-mTOR and p-4E-BP1 were examined separately only p-4E-BP1 remained significant. Our findings indicate that in HCL, critical proteins up- and downstream of mTOR are activated. Moreover, the strong associations with Raf-MEK-ERK signalling imply a possible biologic interaction between these pathways. Most importantly, expression of p-4E-BP1 alone or combined with p-AKT and p-mTOR is of prognostic value in patients with HCL.

Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia

BACKGROUND

BRAF V600E is the genetic lesion underlying hairy-cell leukemia. We assessed the safety and activity of the oral BRAF inhibitor vemurafenib in patients with hairy-cell leukemia that had relapsed after treatment with a purine analogue or who had disease that was refractory to purine analogues.

METHODS

We conducted two phase 2, single-group, multicenter studies of vemurafenib (at a dose of 960 mg twice daily)--one in Italy and one in the United States. The therapy was administered for a median of 16 weeks in the Italian study and 18 weeks in the U.S. study. Primary end points were the complete response rate (in the Italian trial) and the overall response rate (in the U.S. trial). Enrollment was completed (28 patients) in the Italian trial in April 2013 and is still open (26 of 36 planned patients) in the U.S. trial.

RESULTS

The overall response rates were 96% (25 of 26 patients who could be evaluated) after a median of 8 weeks in the Italian study and 100% (24 of 24) after a median of 12 weeks in the U.S. study. The rates of complete response were 35% (9 of 26 patients) and 42% (10 of 24) in the two trials, respectively. In the Italian trial, after a median follow-up of 23 months, the median relapse-free survival was 19 months among patients with a complete response and 6 months among those with a partial response; the median treatment-free survival was 25 months and 18 months, respectively. In the U.S. trial, at 1 year, the progression-free survival rate was 73% and the overall survival rate was 91%. Drug-related adverse events were usually of grade 1 or 2, and the events most frequently leading to dose reductions were rash and arthralgia or arthritis. Secondary cutaneous tumors (treated with simple excision) developed in 7 of 50 patients. The frequent persistence of phosphorylated ERK-positive leukemic cells in bone marrow at the end of treatment suggests bypass reactivation of MEK and ERK as a resistance mechanism.

CONCLUSIONS

A short oral course of vemurafenib was highly effective in patients with relapsed or refractory hairy-cell leukemia. (Funded by the Associazione Italiana per la Ricerca sul Cancro and others; EudraCT number, 2011-005487-13; ClinicalTrials.gov number NCT01711632.).

Clinical features and diagnosis of hairy cell leukemia

Significant advances in the diagnosis and treatment of hairy cell leukemia (HCL) have recently been made. Improved distinction of HCL from its mimics though clinical presentations, morphologic and immunophenotypic features, and more recently molecular biology, has highlighted marked differences in treatment response and overall prognosis between these disorders. As our understanding of the unique pathobiology of HCL has grown, exciting new avenues of treatment as well as insight into immune function have been obtained. This review provides an overview of the clinical features and diagnostic attributes of HCL, with contrast to other mature B cell lymphoproliferative disorders with overlapping features.

Recent advances in diagnosis and treatment of hairy cell leukemia

Hairy cell leukemia (HCL) is a rare, indolent B-cell lymphoproliferative disorder that accounts for 2% of all cases of leukemia. Most patients present with pancytopenia and splenomegaly with variable number of ‘hairy’ lymphocytes in blood. BRAF V600E mutation can be detected in virtually 100% of HCL cases and is absent in other B-cell lymphomas. The mutated gene and its responding abnormal protein can be used as specific markers in the diagnosis of HCL. New therapeutic modalities targeting on mutated BRAF and its downstream pathways have shown encouraging results in clinical trials. The objective of this review article is to discuss the recent developments in the diagnosis and management of hairy cell leukemia.

Immunohistochemical markers in lymphoid malignancies: Protein correlates of molecular alterations

Histomorphology, immunohistochemistry (IHC), and genetics are essential tools for the evaluation and classification of lymphoid malignancies. Advances in diagnostic techniques include the development of immunohistochemical assays that can serve as surrogates for genetic tests. We review the performance of a select subset of assays that detect the aberrant expression of onco-proteins secondary to chromosomal translocations (MYC; BCL2), somatic mutations (BRAF V600E; NOTCH1), and gene copy number gains (CD274 (encoding PD-L1); PDCD1LG2 (encoding PD-L2)) in fixed tissue biopsy sections. We discuss the limitations of IHC, but also its primary advantage over genetics; specifically, its ability to assess the final, common phenotypic consequences of a multitude of genetic and non-genetic events that influence protein expression. The information provided by IHC and genetic testing are thus intimately related; surgical pathologists will increasingly need to interpret and integrate the results of both to provide a comprehensive assessment of tumor biology and guide therapy.

Evaluation of allele-specific PCR and immunohistochemistry for the detection of BRAF V600E mutations in hairy cell leukemia

OBJECTIVES

Detection of BRAF V600E mutations in hairy cell leukemia (HCL) has important diagnostic utility. In this study, we sought to compare immunohistochemistry with an antibody specific for this mutation to a sensitive molecular assay.

METHODS

The performance of the BRAF V600E-specific VE1 antibody was compared with that of allele-specific polymerase chain reaction (PCR) in 22 formalin-fixed, paraffin-embedded (FFPE) specimens with HCL involvement, along with nine splenic marginal zone lymphomas (SMZLs), 10 follicular lymphomas (FLs), 10 mantle cell lymphomas (MCLs), and 10 chronic lymphocytic leukemia/small lymphocytic lymphomas (CLL/SLLs). An additional 11 SMZLs, 100 FLs, 20 MCLs, 83 CLL/SLL specimens, and 49 reactive tonsils within tissue microarrays were stained with VE1.

RESULTS

A BRAF V600E mutation was detected in 17 (77.3%) of 22 HCL cases by PCR. Immunohistochemistry demonstrated VE1 staining in 20 (90.9%) cases, identifying low-level (~1%) involvement in three HCL cases that were mutation negative by PCR. Evaluation of additional material from these patients confirmed the presence of BRAF V600E. Thirty-nine non-HCL cases were negative by both methods. Within tissue microarrays, weak false-positive staining was observed in two (0.8%) of 263 non-HCL cases.

CONCLUSIONS

VE1 immunohistochemistry is more sensitive than allele-specific PCR in FFPE bone marrow specimens and can be applied to decalcified core biopsy specimens that are not appropriate for molecular techniques.

Hairy cell leukemia: short review, today's recommendations and outlook

Hairy cell leukemia (HCL) is part of the low-grade non-Hodgkin lymphoma family and represents approximately 2% of all leukemias. Treatment with splenectomy and interferon-α historically belonged to the first steps of therapeutic options, achieving partial responses/remissions (PR) in most cases with a median survival between 4 and 6 years in the 1980s. The introduction of the purine analogs (PA) pentostatin and cladribine made HCL a well-treatable disease: overall complete response rates (CRR) range from 76 to 98%, with a median disease-free survival (DFS) of 16 years a normal lifespan can be reached and HCL-related deaths are rare. However, insufficient response to PA with poorer prognosis and relapse rates of 30–40% after 5–10 years of follow-up may require alternative strategies. Minimal residual disease can be detected by additional examinations of bone marrow specimens after treatment with PA. The use of immunotherapeutic monoclonal antibodies (mAB) like rituximab as a single agent or in combination with a PA or more recently clinical trials with recombinant immunotoxins (RIT) show promising results to restrict these problems. Recently, the identification of the possible disease-defining BRAF V600E mutation may allow the development of new therapeutic targets.

Localized Langerhans cell histiocytosis of the thymus with BRAF V600E mutation: a case report with immunohistochemical and genetic analyses

We report a case of localized Langerhans cell histiocytosis characterized by clonal aggregation of Langerhans cells in the thymus and identified with molecular genetic study. A 43-year-old Japanese woman was found to have an anterior mediastinal mass by radiologic studies. Laparoscopy-assisted biopsy was subsequently performed. Histologically, we found subtle nodules scattered in the thymus consisting of aggregated Langerhans cells, which caused destruction of Hassall corpuscles. These Langerhans cells were immunohistochemically positive for S-100, CD1a, and CD207/langerin. Using allele-specific polymerase chain reaction and immunohistochemistry with mutation-specific antibody VE1, the BRAF V600E mutation was identified in aggregated Langerhans cells. At the medical follow-up, the thymic tumor had spontaneously regressed; however, identification of oncogenic BRAF mutation supports the neoplastic nature of the current case.

MYD88 L265P somatic mutation: its usefulness in the differential diagnosis of bone marrow involvement by B-cell lymphoproliferative disorders

OBJECTIVES

To examine the usefulness of the MYD88 L265P somatic mutation in identifying cases of lymphoplasmacytic lymphoma (LPL) from other lymphoplasmacytic neoplasms in bone marrow biopsy specimens.

METHODS

We studied 64 bone marrow biopsy specimens with involvement by various small B-cell lymphomas or plasma cell myeloma.

RESULTS

The MYD88 L265P somatic mutation was present in 13/13 cases of LPL, 1/13 cases of hairy cell leukemia, and absent in the other mature B-cell neoplasms tested. A test set of diagnostically challenging bone marrow cases with lymphoplasmacytoid morphology (B-cell lymphoma, not otherwise specified) was selected for additional review and reclassified, without knowledge of the MYD88 L265P status. Of those 16 cases, 7 were positive for MYD88, including 4/4 cases that were reclassified as LPL during the review.

CONCLUSIONS

Although not entirely specific, MYD88 L265P is a useful adjunct for bone marrow diagnosis in separating LPL from other small B-cell lymphomas and plasma cell myeloma.

BRAF V600E-Negative Hairy Cell Leukaemia

Since the initial report of the BRAF V600E mutation in hairy cell leukemia, numerous investigators have demonstrated the presence of this activating mutation in nearly all cases of this disease. A case of hairy cell leukemia is documented with a classical clinical, morphological, immunophenotypic, and cytochemical profile in which the BRAF V600E was not detected. The diagnostic and therapeutic implications are discussed.