Retracing RAS signaling by correlating protein expression in different subtypes of neurofibromatosis 1-associated nerve sheath tumors.

AIMS: Expression patterns of key proteins involved in RAS signaling and connected pathways were determined and correlated to possibly provide information for therapeutic application of RAS inhibitors in neurofibromatosis type 1 (NF1)-associated peripheral nerve sheath tumors (PNST). MATERIALS AND METHODS: Clinical variables (age, sex), histological parameters (cell density, mitoses), and expression of immunohistochemically evaluated ligand and receptor proteins (neuregulin 1 (NRG1), ErbB2, ErbB3), RAS pathway proteins (mTor, Rho, phosphorylated MEK), transcription factors (Pax7, Sox9), and proliferation marker Ki-67, were correlated in cutaneous (CNF, n = 136), diffuse (DNF, n = 123)/diffuse plexiform (DPNF, n = 113), and plexiform neurofibroma (PNF, n = 126), and in malignant PNST (MPNST, n = 22). RESULTS: In CNF, NRG1 correlated with Ki-67 and Pax7. Further, mTOR correlated with ErbB3, Sox9, Pax7, and Ki-67. In DNF/DPNF, expression of NRG1 correlated with pMEK and Pax7. mTOR correlated with pMEK, Sox9, and Pax7. Noteworthy, pMEK was weakly expressed in some DNF but not in DPNF. ErbB3 correlated with mTor and Ki-67. Furthermore, Rho correlated with Pax7 and Ki-67. In PNF, ErbB3 expression was associated with Sox9, mTOR, pMEK, and Pax7 as well as mTOR with Sox9 and Pax7, Rho with pMEK and Pax7, and pMEK with Pax7 and Sox9. In MPNST, only few correlations were observed, ErbB2 correlated with Ki-67, and Rho with pMEK. CONCLUSION: Signaling networks of the RAS pathway could be retraced by correlation analysis of protein expression in subgroups of NF1 associated benign PNST. In regard to treatment of PNST, MEK inhibitors, which are presently evaluated for PNF, may possibly also be effective to some extent in DNF.

Expression of Ras signaling pathway proteins and developmental factors in peripheral nerve sheath tumors of patients with neurofibromatosis type 1.

PURPOSE: To characterize expression of factors relevant for Ras signaling and developmental factors in a large series of peripheral nerve sheath tumors (PNST) obtained from patients with neurofibromatosis type 1 (NF1). MATERIALS AND METHODS: Tissue micro-array technique was applied to study 520 PNST of 385 NF1 patients by immunohistochemistry for mTor, Rho, phosphorylated MEK, Pax7, Sox9, and periaxin expression. PNST comprised cutaneous neurofibroma (CNF) (n = 114), diffuse neurofibroma (DNF) (n = 109), diffuse plexiform neurofibroma (DPNF) (n = 108), plexiform neurofibroma (PNF) (n = 110), and malignant PNST (MPNST) (n = 22). RESULTS: All proteins examined showed highest expression levels/highest frequency of expression in MPNST. Benign PNF with potential for malignant dedifferentiation expressed mTor, phosphorylated MEK, Sox9, and periaxin significantly higher/more frequently than other benign neurofibroma subtypes. CONCLUSION: In NF1-associated PNST, expression of proteins involved in Ras-signaling and development is upregulated not only in MPNST, but also in benign PNF with the potential for malignant dedifferentiation. The differences in protein expression may provide clues for understanding the therapeutic effects of substances applied for reduction of PNST in NF1.

ERBB2 and ERBB3 Growth Factor Receptors, Neuregulin-1, CD44 and Ki-67 Proliferation Index in Neurofibromatosis Type 1-associated Peripheral Nerve Sheath Tumors.

AIM: To characterize the growth pattern and antigen profile of peripheral nerve sheaths tumors (PNST) in a large series of tumors obtained from patients with neurofibromatosis type 1 (NF1). MATERIALS AND METHODS: Tissue micro-array technique was applied to study 520 PNSTs of 385 patients with NF1 by immunohistochemistry for human epidermal growth factor receptors erb-b2 receptor tyrosine kinase 2 (ERBB2) and ERBB3, CD44, neuroregulin (NRG1) and proliferation index by Ki-67. PNSTs were classified as cutaneous neurofibroma (CNF) in 114 cases, diffuse neurofibroma (DNF) in 109, diffuse plexiform neurofibroma (DPNF) in 108, plexiform neurofibroma (PNF) in 110, and malignant PNST (MPNST) in 22. RESULTS: The Ki-67 proliferation index was significantly higher in MPNST than in benign PNST (p<0.001). ERBB2 expression was significantly lower in PNST with diffuse growth than in PNF and MPNST (p<0.001). ERBB3 expression was also higher in PNF and MPNST (both p<0.001) than in diffuse PNST. NRG1 expression was significantly higher in PNF than in non-encapsulated benign PNST or MPNST (both p<0.001). Co-expression of ERBB2, ERBB3 and ligand NRG1 was rare, mainly observed in PNST with a plexiform component (in four PNFs, nine DPNFs, one CNF, and two MPNSTs). Expression of CD44 in contrast was significantly stronger in diffusely growing PNST than in PNF (p<0.001). CONCLUSION: Growth factor receptors ERBB2 and ERBB3 were significantly up-regulated in PNF and MPNST. The antigen expression pattern of DPNF resembled that of benign PNST with diffuse growth pattern rather than that of encapsulated PNF. Differentiating PNST may be important for the assessment of neurofibroma progression, and for the expected impact of drugs currently used for tumor reduction.

Peripheral Nerve Sheath Tumors in Patients With Neurofibromatosis Type 1: Morphological and Immunohistochemical Study.

BACKGROUND/AIM: The aim of the present investigation was to characterize the growth pattern and antigen profile of peripheral nerve sheath tumors (PNST) in a large series of tumors obtained from patients with Neurofibromatosis type 1 (NF1) focusing on morphological characteristics of diffuse plexiform neurofibroma (DPNF). MATERIALS AND METHODS: Tissue micro-array (TMA) analysis was applied to study 520 formalin-fixed, paraffin-embedded human PNST of 385 patients with confirmed NF1 diagnosis. PNST originated from all areas of the body and were classified as cutaneous neurofibroma (CNF, n=114), diffuse neurofibroma (DNF, n=109), DPNF (n=108), plexiform neurofibroma (PNF, n=110), and malignant peripheral nerve sheath tumor (MPNST, n=22). Histomorphology and antigen expression patterns of the tumors were determined [S100, epithelial membrane antigen (EMA), CD90, mast cell tryptase, and neurofilament]. RESULTS: Benign PNST showed significantly more S100-positive tumor cells than MPNST (p<0.001). EMA expression was most pronounced in perineurium of DPNF. The number of mast cells in CNF, DNF and DPNF was significantly higher compared to PNF and MPNST (p<0.001 for both comparisons, Mann-Whitney U-test). CONCLUSION: DPNF show some distinct cellular characteristics. A high number of EMA positive cells possibly indicates the dissemination of perineural cells to the surrounding tissue. Concerning mast cell density, DPNF resemble DNF and CNS rather than PNF. Close contact of tumor cells in DPNF, DNF and CNF with the immune system is a prerequisite for permanent immunological reactions in contrast to PNF in which tumor cells are partitioned from the immune system by the perineurium and blood-nerve barrier of blood vessels. It is assumed that these morphological distinctions may reflect in part the biological differences between the entities. While PNF is a known precancerous stage in NF1 patients, DPNF are not rated as such. Furthermore, the morphologic differences between benign nerve sheath tumors may be important for the efficacy of drugs to access tumor cells.