BCRP expression in schwannoma, plexiform neurofibroma and MPNST.

BACKGROUND: peripheral nerve sheath tumors comprise a broad spectrum of neoplasms. Vestibular schwannomas and plexiform neurofibromas are symptomatic albeit benign, but a subset of the latter pre-malignant lesions will transform to malignant peripheral nerve sheath tumors (MPNST). Surgery and radiotherapy are the primary strategies to treat these tumors. Intrinsic resistance to drug therapy characterizes all three tumor subtypes. The breast cancer resistance protein BCRP is a transmembrane efflux transporter considered to play a key role in various biological barriers such as the blood brain barrier. At the same time it is associated with drug resistance in various tumors. Its potential role in drug resistant tumors of the peripheral nervous system is largely unknown. OBJECTIVE: to assess if BCRP is expressed in vestibular schwannomas, plexiform neurofibromas and MPNST. MATERIAL AND METHODS: immunohistochemical staining for BCRP was performed on a tissue microarray composed out of 22 vestibular schwannomas, 10 plexiform neurofibromas and 18 MPNSTs. RESULTS: sixteen out of twenty-two vestibular schwannomas (73%), nine out of ten plexiform neurofibromas (90%) and six out of eighteen MPNST (33%) expressed BCRP in the vasculature. Tumor cells were negative. CONCLUSION: BCRP is present in the vasculature of vestibular schwannomas, plexiform neurofibromas and MPSNT. Therefore, it may reduce the drug exposure of underlying tumor tissues and potentially cause failure of drug therapy.

Loss of H3K27 tri-methylation is a diagnostic marker for malignant peripheral nerve sheath tumors and an indicator for an inferior survival.

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas that can show overlapping features with benign neurofibromas as well as high-grade sarcomas. Additional diagnostic markers are needed to aid in this often challenging differential diagnosis. Recently mutations in two critical components of the polycomb repressor 2 (PRC2) complex, SUZ12 and EED, were reported to occur specifically in MPNSTs while such mutations are absent in neurofibromas, both in the setting of neurofibromatosis (NF) and sporadic cases. Furthermore, both SUZ12 and EED mutations in MPNSTs were associated with loss of H3K27 tri-methylation, a downstream target of PRC2. Therefore, we tested whether H3K27me3 immunohistochemistry is useful as a diagnostic and prognostic marker for MPNSTs. We performed H3K27me3 immunohistochemistry in 162 primary MPNSTs, 97 neurofibromas and 341 other tumors using tissue microarray. We observed loss of H3K27me3 in 34% (55/162) of all MPNSTs while expression was retained in all neurofibromas including atypical (n=8) and plexiform subtypes (n=24). Within other tumors we detected loss of H3K27me3 in only 7% (24/341). Surprisingly, 60% (9/15) of synovial sarcomas and 38% (3/8) of fibrosarcomatous dermatofibrosarcoma protuberans (DFSP) showed loss of H3K27 trimethylation. Only 1 out of 44 schwannomas showed loss of H3K27me3 and all 4 perineuriomas showed intact H3K27me3. Furthermore, MPNSTs with loss of H3K27 tri-methylation showed inferior survival compared with MPNSTs with intact H3K27 tri-methylation, which was validated in two independent cohorts. Our results indicate that H3K27me3 immunohistochemistry is useful as a diagnostic marker, in which loss of H3K27me3 favors MPNST above neurofibroma. However, H3K27me3 immunohistochemistry is not suitable to distinguish MPNST from its morphological mimicker synovial sarcoma or fibrosarcomatous DFSP. Since loss of H3K27 tri-methylation was related to poorer survival in MPNST, chromatin modification mediated by this specific histone seems to orchestrate more aggressive tumour biology.

Tumor Biology of Vestibular Schwannoma: A Review of Experimental Data on the Determinants of Tumor Genesis and Growth Characteristics.

OBJECTIVE: Provide an overview of the literature on vestibular schwannoma biology with special attention to tumor behavior and targeted therapy. BACKGROUND: Vestibular schwannomas are benign tumors originating from the eighth cranial nerve and arise due to inactivation of the NF2 gene and its product merlin. Unraveling the biology of these tumors helps to clarify their growth pattern and is essential in identifying therapeutic targets. METHODS: PubMed search for English-language articles on vestibular schwannoma biology from 1994 to 2014. RESULTS: Activation of merlin and its role in cell signaling seem as key aspects of vestibular schwannoma biology. Merlin is regulated by proteins such as CD44, Rac, and myosin phosphatase-targeting subunit 1. The tumor-suppressive functions of merlin are related to receptor tyrosine kinases, such as the platelet-derived growth factor receptor and vascular endothelial growth factor receptor. Merlin mediates the Hippo pathway and acts within the nucleus by binding E3 ubiquiting ligase CRL4. Angiogenesis is an important mechanism responsible for the progression of these tumors and is affected by processes such as hypoxia and inflammation. Inhibiting angiogenesis by targeting vascular endothelial growth factor receptor seems to be the most successful pharmacologic strategy, but additional therapeutic options are emerging. CONCLUSION: Over the years, the knowledge on vestibular schwannoma biology has significantly increased. Future research should focus on identifying new therapeutic targets by investigating vestibular schwannoma (epi)genetics, merlin function, and tumor behavior. Besides identifying novel targets, testing new combinations of existing treatment strategies can further improve vestibular schwannoma therapy.

Tumor-associated macrophages are related to volumetric growth of vestibular schwannomas.

HYPOTHESIS: Tumor-associated macrophages contribute to vestibular schwannoma development. OBJECTIVE: An important clinical problem regarding vestibular schwannoma treatment is their variable growth rate. Tumor biological research can help to clarify this growth rate and may offer targets for therapy. Inflammation is an important biological process involved in the development of many solid tumors. Macrophages are major determinants of intratumoral inflammation. Macrophages can be divided into two groups; the M1- and M2-type macrophages. M2-type macrophages are associated with tumor-promoting processes like angiogenesis, tumor cell growth, and downregulation of the antitumor immune response. Both macrophages and angiogenesis can serve as targets for therapy. CD163 is a specific marker for M2-type macrophages. The goal of this study was to investigate if the expression of CD163 positive macrophages in sporadic vestibular schwannomas is associated with angiogenesis and tumor growth. METHODS: CD163 expression in 10 fast-growing vestibular schwannomas was compared with CD163 expression in 10 slow-growing vestibular schwannomas. Tumor growth was determined by comparing preoperative tumor volume measurements on MRI. The relation between macrophage expression and angiogenesis was evaluated by assessing microvessel density (CD31). RESULTS: CD163 expression and microvessel density were significantly higher in fast-growing vestibular schwannomas (p < 0.001 and p = 0.019, respectively). Tumors with higher CD163 expression contained significantly more microvessels (p = 0.014). CONCLUSION: This study demonstrates that M2-type macrophages in vestibular schwannomas relate to angiogenesis and volumetric tumor growth. These results imply that the M2-type macrophage infiltrate contributes to progressive tumor growth, making it a potential target for pharmacologic therapy.

Mutations affecting BRAF, EGFR, PIK3CA, and KRAS are not associated with sporadic vestibular schwannomas.

Sporadic vestibular schwannomas are benign tumors originating from the Schwann cells of the vestibular portion of the eigth cranial nerve. An important clinical hallmark of these tumors is their variable growth rate. Investigating vestibular schwannoma biology can help to clarify this variable growth rate and may offer targets for therapeutic treatment. A recent mutation analysis on sporadic non-head and neck schwannomas detected BRAF mutations in around 20 % of tumors. BRAF is part of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. MAPK/ERK activation is associated with an uncontrolled cell growth. Mutated BRAF can function as a target to inhibit this pathway. Mutations in BRAF and other members of the MAPK/ERK pathway have not been investigated in sporadic vestibular schwannomas before. The goal of this study was to investigate if these mutations are present in vestibular schwannomas and whether these mutations correlate with tumor growth. Tumor specimens of 48 patients surgically treated for a sporadic vestibular schwannoma were analyzed. An allele-specific quantitative real-time PCR assay was performed to detect the 13 most frequent mutations affecting BRAF, EGFR, PIK3CA, and KRAS. Radiologically measured tumor growth was included in the analysis to identify potential relationships between these mutations and tumor progression. No activating hotspot mutations in BRAF, EGFR, PIK3CA, or KRAS were detected. The 13 most frequent mutations affecting BRAF, EGFR, PIK3CA, and KRAS are not involved in sporadic vestibular schwannoma development. These results are in contrast to the recent detection of these BRAF mutations in non-head and neck schwannomas.

Intratumoral hemorrhage, vessel density, and the inflammatory reaction contribute to volume increase of sporadic vestibular schwannomas.

Vestibular schwannomas show a large variation in growth rate, making prediction and anticipation of tumor growth difficult. More accurate prediction of clinical behavior requires better understanding of tumor biological factors influencing tumor progression. Biological processes like intratumoral hemorrhage, cell proliferation, microvessel density, and inflammation were analyzed in order to determine their role in vestibular schwannoma development. Tumor specimens of 67 patients surgically treated for a histologically proven unilateral vestibular schwannoma were studied. Preoperative magnetic resonance imaging (MRI) scans were used to determine tumor size and to classify tumors as homogeneous, inhomogeneous, and cystic. Immunohistochemical studies evaluated cell proliferation (histone H3 and Ki-67), microvessel density (CD31), and inflammation (CD45 and CD68). Intratumoral hemorrhage was assessed by hemosiderin deposition. The expression patterns of these markers were compared with tumor size, tumor growth index, MRI appearance, patients' age, and duration of symptoms. No relation between cell proliferation and clinical signs of tumor volume increase or MRI appearance was found. Intratumoral hemosiderin, microvessel density, and inflammation were significantly positively correlated with tumor size and the tumor growth index. Cystic and inhomogeneous tumors showed significantly more hemosiderin deposition than homogeneous tumors. The microvessel density was significantly higher in tumors with a high number of CD68-positive cells. The volume increase of vestibular schwannomas is not based on cell proliferation alone. Factors like intratumoral bleeding, (neo)vascularization, and intensity of the inflammatory reaction also influence tumor volume.