BRAF--a new player in hematological neoplasms

Differential contribution for ERK1 and ERK2 kinases in BRAFV600E-triggered phenotypes in adult mouse models

The BRAF gene is mutated in a plethora of human cancers. The majority of such molecular lesions result in the expression of a constitutively active BRAF variant (BRAFV600E) which continuously bolsters cell proliferation. Although we recently addressed the early effects triggered by BRAFV600E-activation, the specific contribution of ERK1 and ERK2 in BRAFV600E-driven responses in vivo has never been explored. Here we describe the first murine model suitable for genetically dissecting the ERK1/ERK2 impact in multiple phenotypes induced by ubiquitous BRAFV600E-expression. We unveil that ERK1 is dispensable for BRAFV600E-dependent lifespan shortening and for BRAFV600E-driven tumor growth. We show that BRAFV600E-expression provokes an ERK1-independent lymphocyte depletion which does not rely on p21CIP1-induced cell cycle arrest and is unresponsive to ERK-chemical inhibition. Moreover, we also reveal that ERK1 is dispensable for BRAFV600E-triggered cytotoxicity in lungs and that ERK-chemical inhibition abrogates some of these detrimental effects, such as DNA damage, in Club cells but not in pulmonary lymphocytes. Our data suggest that ERK1/ERK2 contribution to BRAFV600E-driven phenotypes is dynamic and varies dependently on cell type, the biological function, and the level of ERK-pathway activation. Our findings also provide useful insights into the comprehension of BRAFV600E-driven malignancies pathophysiology as well as the consequences in vivo of novel ERK pathway-targeted anti-cancer therapies.

Onco-immunomodulatory properties of pharmacological interference with RAS-RAF-MEK-ERK pathway hyperactivation

Hyperactivation of the RAS-RAF-MEK-ERK cascade - a mitogen-activated protein kinase pathway – has a well-known association with oncogenesis of leading tumor entities, including non-small cell lung cancer, colorectal carcinoma, pancreatic ductal adenocarcinoma, and malignant melanoma. Increasing evidence shows that genetic alterations leading to RAS-RAF-MEK-ERK pathway hyperactivation mediate contact- and soluble-dependent crosstalk between tumor, tumor microenvironment (TME) and the immune system resulting in immune escape mechanisms and establishment of a tumor-sustaining environment. Consequently, pharmacological interruption of this pathway not only leads to tumor-cell intrinsic disruptive effects but also modification of the TME and anti-tumor immunomodulation. At the same time, the importance of ERK signaling in immune cell physiology and potentiation of anti-tumor immune responses through ERK signaling inhibition within immune cell subsets has received growing appreciation. Specifically, a strong case was made for targeted MEK inhibition due to promising associated immune cell intrinsic modulatory effects. However, the successful transition of therapeutic agents interrupting RAS-RAF-MEK-ERK hyperactivation is still being hampered by significant limitations regarding durable efficacy, therapy resistance and toxicity. We here collate and summarize the multifaceted role of RAS-RAF-MEK-ERK signaling in physiology and oncoimmunology and outline the rationale and concepts for exploitation of immunomodulatory properties of RAS-RAF-MEK-ERK inhibition while accentuating the role of MEK inhibition in combinatorial and intermittent anticancer therapy. Furthermore, we point out the extensive scientific efforts dedicated to overcoming the challenges encountered during the clinical transition of various therapeutic agents in the search for the most effective and safe patient- and tumor-tailored treatment approach.

The Dual Role of Autophagy in Crizotinib-Treated ALK+ ALCL: From the Lymphoma Cells Drug Resistance to Their Demise

Autophagy has been described as harboring a dual role in cancer development and therapy. Depending on the context, it can exert either pro-survival or pro-death functions. Here, we review what is known about autophagy in crizotinib-treated ALK⁺ ALCL. We first present our main findings on the role and regulation of autophagy in these cells. Then, we provide literature-driven hypotheses that could explain mechanistically the pro-survival properties of autophagy in crizotinib-treated bulk and stem-like ALK⁺ ALCL cells. Finally, we discuss how the potentiation of autophagy, which occurs with combined therapies (ALK and BCL2 or ALK and RAF1 co-inhibition), could convert it from a survival mechanism to a pro-death process.

BRAF V600E Mutation: A Significant Biomarker for Prediction of Disease Relapse in Pediatric Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) is a rare disease presenting with usually a localized disease but sometimes a widespread aggressive disorder especially in children. Among the somatic mutations in RAF-MEK-ERK pathway, especially BRAF mutation has been detected so far in LCH. We aimed in this study to investigate the prognostic significance of the mutations of target genes playing a role in the RAF-MEK-ERK pathway in pediatric LCH. Mutation analyses were performed on tumor DNA extracted from formalin-fixed paraffin-embedded biopsy specimens of 38 pediatric LCH cases using a direct sequencing technique for BRAF, ARAF, MAP2K1, and MAP3K1 genes. The mutational status was correlated statistically with survival, clinical progression (disease relapse), and the established clinical prognostic parameters of LCH such as age, gender, localization, multisystem disease, central nervous system risk lesions, and risk organ or special-site involvement. BRAF V600E mutation was detected in 14 cases (36.8%), whereas ARAF mutation was found in only 1 case. No mutations were identified for MAP2K1 and MAP3K1 genes. The association of BRAF V600E mutation was significant in children with multisystem disease, younger age (<2 years), skin, and special organ involvement. BRAF V600E mutation was an independent predictive parameter for disease relapse. We therefore conclude that BRAF V600E mutation may be a significant marker for predicting disease progression in LCH and a candidate for targeted therapy for children with disease relapse and multisystem disease.

Langerhans cell histiocytosis in children: History, classification, pathobiology, clinical manifestations, and prognosis

Langerhans cell histiocytosis (LCH) is an inflammatory neoplasia of myeloid precursor cells driven by mutations in the mitogen-activated protein kinase pathway. When disease involves the skin, LCH most commonly presents as a seborrheic dermatitis or eczematous eruption on the scalp and trunk. Evaluation for involvement of other organ systems is essential, because 9 of 10 patients presenting with cutaneous disease also have multisystem involvement. Clinical manifestations range from isolated disease with spontaneous resolution to life-threatening multisystem disease. Prognosis depends on involvement of risk organs (liver, spleen, and bone marrow) at diagnosis, particularly on presence of organ dysfunction, and response to initial therapy. Systemic treatment incorporating steroids and cytostatic drugs for at least one year has improved prognosis of multisystem LCH and represents the current standard of care.

Liquid biopsy to monitor melanoma patients

During the last six years, several innovative, systemic therapies for the treatment of metastatic malignant melanoma (MM) have emerged. Conventional chemotherapy has been superseded by novel first-line therapies, including systemic immunotherapies (anti-CTLA4 and anti-PD1; authorization of anti-PDL1 is anticipated) and therapies targeting specific mutations (BRAF, NRAS, and c-KIT). Thus, treating physicians are confronted with new challenges, such as stratifying patients for appropriate treatments and monitoring long-term responders for progression. Consequently, reliable methods for monitoring disease progression or treatment resistance are necessary. Localized and advanced cancers may generate circulating tumor cells and circulating tumor DNA (ctDNA) that can be detected and quantified from peripheral blood samples (liquid biopsy). For melanoma patients, liquid biopsy results may be useful as novel predictive biomarkers to guide therapeutic decisions, particularly in the context of mutation-based targeted therapies. The challenges of using liquid biopsy include strict criteria for the phenotypic nature of circulating MM cells or their fragments and the instability of ctDNA in blood. The limitations of liquid biopsy in routine diagnostic testing are discussed in this review.

Erdheim-Chester disease: description of two illustrative cases involving the lung

AIM

Erdheim-Chester disease represents a clonal systemic proliferation of histiocytes. Bone is the most common site of involvement, although almost any organ, including the lungs, can be affected.

METHODS AND RESULTS

The diagnosis of Erdheim-Chester disease can be difficult, owing to its rarity and protean presentation. Correlation between clinical, radiological and histological findings is mandatory for identification of the disease. Foamy histiocytes, lacking Langerhans cell markers, represent the typical histological findings, although their absence does not rule out Erdheim-Chester disease. Identification of BRAF mutation can be helpful in making the diagnosis, and allows for the development and application of targeted therapies in this setting.

CONCLUSIONS

Herein, we describe two cases presenting with lung involvement and vertebral lesions, lacking the more typical long-bone involvement. One case histologically mimicked Rosai-Dorfman disease. However, both cases harboured the pathognomonic BRAFV600E mutation.

Langerhans cell histiocytosis: a comprehensive review

Langerhans cell histiocytosis (LCH) is currently regarded as a myeloid neoplasm, with remarkably broad clinical spectrum, ranging from isolated skin or bone lesions to a disseminated disease that can involve nearly any organ. LCH is generally regarded as a sporadic disease that occurs predominantly in the paediatric population. The diagnosis of LCH is confirmed by immunohistochemistry (IHC) by demonstrating the presence of dendritic cell markers such as S100 protein, in addition to CD1a and langerin. Contrary to previous beliefs, recent literature reveals that the pathogenesis of LCH might involve a clonal process implicating BRAF c.1799T>A (p.Val600Glu) and other mutations [(600DLAT) B-RAF and (T599A) B-RAF, somatic MAP2K1 mutations].Through this review article, we have summarised the latest understanding of the biological and salient histological characteristics of LCH and its potential morphological mimics.

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.

The Cancer Genomics Resource List 2014

CONTEXT

Genomic sequencing for cancer is offered by commercial for-profit laboratories, independent laboratory networks, and laboratories in academic medical centers and integrated health networks. The variability among the tests has created a complex, confusing environment.

OBJECTIVE

To address the complexity, the Personalized Health Care (PHC) Committee of the College of American Pathologists proposed the development of a cancer genomics resource list (CGRL). The goal of this resource was to assist the laboratory pathology and clinical oncology communities.

DESIGN

The PHC Committee established a working group in 2012 to address this goal. The group consisted of site-specific experts in cancer genetic sequencing. The group identified current next-generation sequencing (NGS)-based cancer tests and compiled them into a usable resource. The genes were annotated by the working group. The annotation process drew on published knowledge, including public databases and the medical literature.

RESULTS

The compiled list includes NGS panels offered by 19 laboratories or vendors, accompanied by annotations. The list has 611 different genes for which NGS-based mutation testing is offered. Surprisingly, of these 611 genes, 0 genes were listed in every panel, 43 genes were listed in 4 panels, and 54 genes were listed in 3 panels. In addition, tests for 393 genes were offered by only 1 or 2 institutions. Table 1 provides an example of gene mutations offered for breast cancer genomic testing with the annotation as it appears in the CGRL 2014.

CONCLUSIONS

The final product, referred to as the Cancer Genomics Resource List 2014, is available as supplemental digital content.

Immunohistochemistry for BRAF V600E in the Differential Diagnosis of Hairy Cell Leukemia vs Other Splenic B-Cell Lymphomas

OBJECTIVES

Recent reports have used immunohistochemistry (IHC) with a mutation-specific antibody to detect the BRAF V600E mutation, which is found in nearly all cases of hairy cell leukemia (HCL). To date, however, only a small number of non-HCL, splenic B-cell lymphomas have been examined by IHC.

METHODS

We analyzed 121 cases, including 26 HCLs, 52 non-HCL splenic lymphomas, 22 chronic lymphocytic leukemias/small lymphocytic lymphomas (CLLs/SLLs), and 21 plasma cell neoplasms (PCNs) for BRAF V600E expression by IHC. Molecular testing for BRAF V600E was performed in a subset of cases, using allele-specific polymerase chain reaction and/or Sanger sequencing.

RESULTS

Twenty-six (100%) of 26 HCL cases were positive by IHC vs one (1%) of 95 non-HCL cases. Positive staining was identified in one (2%) of 44 splenic marginal zone lymphomas (SMZLs), while each of 22 CLLs/SLLs, 21 PCNs, six unclassifiable splenic lymphomas, and two HCL variants were negative. IHC and molecular results were concordant in all cases examined (21 HCLs and 21 non-HCLs, including the BRAF+ SMZLs).

CONCLUSIONS

The detection of BRAF V600E by IHC is useful in the distinction of HCLs from other splenic-based lymphomas, although the identification of at least rare SMZLs containing this abnormality illustrates the continuing need for a multiparameter approach to diagnosis.

Aberrant splicing of U12-type introns is the hallmark of ZRSR2 mutant myelodysplastic syndrome

Somatic mutations in the spliceosome gene ZRSR2 — located on the X chromosome — are associated with myelodysplastic syndrome (MDS). ZRSR2 is involved in the recognition of 3΄ splice site during the early stages of spliceosome assembly; however, its precise role in RNA splicing has remained unclear. Here, we characterize ZRSR2 as an essential component of the minor spliceosome (U12-dependent) assembly. shRNA mediated knockdown of ZRSR2 leads to impaired splicing of the U12-type introns, and RNA-Sequencing of MDS bone marrow reveals that loss of ZRSR2 activity causes increased mis-splicing. These splicing defects involve retention of the U12-type introns while splicing of the U2-type introns remain mostly unaffected. ZRSR2 deficient cells also exhibit reduced proliferation potential and distinct alterations in myeloid and erythroid differentiation in vitro. These data identify a specific role for ZRSR2 in RNA splicing and highlight dysregulated splicing of U12-type introns as a characteristic feature of ZRSR2 mutations in MDS.

The utility of BRAF V600E mutation-specific antibody VE1 for the diagnosis of hairy cell leukemia

OBJECTIVES

BRAF V600E mutation is characteristic of hairy cell leukemia (HCL). A V600E mutation-specific antibody, VE1, has been recently developed. We studied the diagnostic utility of this antibody in HCL and compared it with other B-cell neoplasms.

METHODS

VE1 activity was assessed using immunohistochemistry in 90 mature B-cell neoplasms, including HCL (n = 17), HCL variant (n = 6), chronic lymphocytic leukemia (CLL) (n = 20), and 47 other B-cell lymphomas. Most (87/90) specimens were formalin-fixed, paraffin-embedded bone marrow (BM) biopsy specimens decalcified in either hydrochloric acid or formic acid.

RESULTS

VE1 was positive in 15 (88%) cases of HCL and two (10%) cases of CLL and was negative in all other tumors assessed. The VE1-positive HCL cases showed uniform staining in all tumor cells, but intensity was variable. The two VE1-negative HCL cases had BRAF V600 mutations proven by molecular analysis. The two CLL cases positive with VE1 showed an atypical staining pattern with expression in a minority of lymphoma cells. Immunohistochemistry using the VE1 antibody had a sensitivity of 88% and a specificity of 97% for HCL.

CONCLUSIONS

VE1 immunohistochemistry is a useful and convenient surrogate for detecting BRAF V600E mutation in BM biopsy specimens decalcified with hydrochloric or formic acid-based solutions.

Best practice of BRAF V600E mutation testing for the diagnosis and management of thyroid cancers

BRAF V600E mutation is the single most common genetic alteration identified in papillary thyroid carcinoma. There is significant association between BRAF V600E mutation and aggressive tumor behavior. BRAF V600E mutation has also been found to be an independent predictor of treatment failure and tumor recurrence even in patients with low-stage disease. Pre-operative BRAF mutation testing of thyroid fine needle aspiration specimens has become a routine clinical practice that enhances the predictability of malignancy in indeterminate fine needle aspiration cytology specimens especially those in the follicular lesion of undetermined significance/atypia of undetermined significance category. In addition to histological evaluation of subsequent core needle biopsy and BRAF immunohistochemistry, an expanded panel of mutation testing including BRAF V600E, NRAS, HRAS, RET/papillary thyroid carcinoma and PAX8/PPARγ rearrangements are currently advocated to further improve the diagnostic predictability in the detection of thyroid carcinomas using cytological specimens.