HLA-I levels correlate with survival outcomes in response to immune checkpoint inhibitors in non-small cell lung cancer.

OBJECTIVES: Immune checkpoint inhibitors (ICIs) have provided a breakthrough in the treatment of non-small cell lung cancer (NSCLC) patients, but only some patients benefit substantively. Identifying definitive predictive biomarkers could overcome this limitation. MATERIALS AND METHODS: We selected 146 metastatic NSCLC patients treated with anti-PD-(L)1. Immunohistochemistry of HLA-I, PD-L1 and CD73 was performed in 122 tumor biopsies at diagnosis. The association with patients, tumor parameters, and the predictive value to ICI treatment were determined. RESULTS: In our cohort, 42 %, 25 %, and 21 % of the tumors exhibited high levels of HLA-I, PD-L1, and CD73, respectively. Lung adenocarcinomas displayed elevated CD73 levels, compared with lung squamous cell carcinomas (P = 0.026). High PD-L1 was significantly correlated with high levels of HLA-I (P = 0.005) and of CD73 (P = 0.025). Patients with high-level HLA-I tumors exhibited more favorable clinical outcomes following ICI, with a median overall survival of 30.7 months (95 % confidence interval [CI]: 18.3 months-not reached), compared with 18.2 months (95 % CI: 12.4-25.2 months) in patients with low-level HLA-I tumors (P = 0.016). The median progression-free survival (PFS) for patients with high-level HLA-I tumors was 18.5 months (95 % CI: 11.1-57.1 months), longer than patients with low-level HLA-I tumors, whose median PFS was 9.2 months (95 % CI: 7.2-11.9 months) (P = 0.006). In a multivariable analysis, high-level HLA-I was independently associated with lower risk of progression to ICI (HR = 0.46, 95 % CI 0.24-0.87; P = 0.018). CONCLUSIONS: High-level HLA-I were associated with better clinical outcomes to ICI in our cohort of NSCLC patients. Therefore, further investigations are warranted to refine this biomarker and validate its efficacy in prospective and larger set of patients.

MYC activation impairs cell-intrinsic IFNγ signaling and confers resistance to anti-PD1/PD-L1 therapy in lung cancer.

Elucidating the adaptive mechanisms that prevent host immune response in cancer will help predict efficacy of anti-programmed death-1 (PD1)/L1 therapies. Here, we study the cell-intrinsic response of lung cancer (LC) to interferon-γ (IFNγ), a cytokine that promotes immunoresponse and modulates programmed death-ligand 1 (PD-L1) levels. We report complete refractoriness to IFNγ in a subset of LCs as a result of JAK2 or IFNGR1 inactivation. A submaximal response affects another subset that shows constitutive low levels of IFNγ-stimulated genes (IγSGs) coupled with decreased H3K27ac (histone 3 acetylation at lysine 27) deposition and promoter hypermethylation and reduced IFN regulatory factor 1 (IRF1) recruitment to the DNA on IFNγ stimulation. Most of these are neuroendocrine small cell LCs (SCLCs) with oncogenic MYC/MYCL1/MYCN. The oncogenic activation of MYC in SCLC cells downregulates JAK2 and impairs IγSGs stimulation by IFNγ. MYC amplification tends to associate with a worse response to anti-PD1/L1 therapies. Hence alterations affecting the JAK/STAT pathway and MYC activation prevent stimulation by IFNγ and may predict anti-PD1/L1 efficacy in LC.

Biological and clinical perspectives of the actionable gene fusions and amplifications involving tyrosine kinase receptors in lung cancer.

Identifying molecular oncogenic drivers is crucial for precision oncology. Genetic rearrangements, including gene fusions and gene amplification, involving and activating receptor tyrosine kinases (RTKs) are recurrent in solid tumors, particularly in non-small cell lung cancer. Advances in the tools to detect these alterations have deepened our understanding of the underlying biology and tumor characteristics and have prompted the development of novel inhibitors targeting activated RTKs. Nowadays, druggable oncogenic rearrangements are found in around 15% of lung adenocarcinomas. However, taken separately, each of these alterations has a low prevalence, which poses a challenge to their diagnosis. The identification and characterization of novel targetable oncogenic rearrangements in lung cancer continue to expand, as shown by the recent discovery of the CLIP1-LTK fusion found in 0.4% of lung adenocarcinomas. While tyrosine kinase inhibitors that block the activity of RTKs have represented a breakthrough in the therapeutic landscape by improving the prognosis of this disease, prolonged treatment inevitably leads to the development of acquired resistance. Here, we review the oncogenic fusions and gene amplifications involving RTK in lung cancer. We address the genetic and molecular structure of oncogenic RTKs and the methods to diagnose them, emphasizing the role of next-generation sequencing technologies. Furthermore, we discuss the therapeutic implications of the different tyrosine kinase inhibitors, including the current clinical trials and the mechanisms responsible for acquired resistance. Finally, we provide an overview of the use of liquid biopsies to monitor the course of the disease.

Efficacy of CDK4/6 inhibitors in preclinical models of malignant pleural mesothelioma.

BACKGROUND: There is no effective therapy for patients with malignant pleural mesothelioma (MPM) who progressed to platinum-based chemotherapy and immunotherapy. METHODS: We aimed to investigate the antitumor activity of CDK4/6 inhibitors using in vitro and in vivo preclinical models of MPM. RESULTS: Based on publicly available transcriptomic data of MPM, patients with CDK4 or CDK6 overexpression had shorter overall survival. Treatment with abemaciclib or palbociclib at 100 nM significantly decreased cell proliferation in all cell models evaluated. Both CDK4/6 inhibitors significantly induced G1 cell cycle arrest, thereby increasing cell senescence and increased the expression of interferon signalling pathway and tumour antigen presentation process in culture models of MPM. In vivo preclinical studies showed that palbociclib significantly reduced tumour growth and prolonged overall survival using distinct xenograft models of MPM implanted in athymic mice. CONCLUSIONS: Treatment of MPM with CDK4/6 inhibitors decreased cell proliferation, mainly by promoting cell cycle arrest at G1 and by induction of cell senescence. Our preclinical studies provide evidence for evaluating CDK4/6 inhibitors in the clinic for the treatment of MPM.

SMARCA4 deficient tumours are vulnerable to KDM6A/UTX and KDM6B/JMJD3 blockade.

Despite the genetic inactivation of SMARCA4, a core component of the SWI/SNF-complex commonly found in cancer, there are no therapies that effectively target SMARCA4-deficient tumours. Here, we show that, unlike the cells with activated MYC oncogene, cells with SMARCA4 inactivation are refractory to the histone deacetylase inhibitor, SAHA, leading to the aberrant accumulation of H3K27me3. SMARCA4-mutant cells also show an impaired transactivation and significantly reduced levels of the histone demethylases KDM6A/UTX and KDM6B/JMJD3, and a strong dependency on these histone demethylases, so that its inhibition compromises cell viability. Administering the KDM6 inhibitor GSK-J4 to mice orthotopically implanted with SMARCA4-mutant lung cancer cells or primary small cell carcinoma of the ovary, hypercalcaemic type (SCCOHT), had strong anti-tumour effects. In this work we highlight the vulnerability of KDM6 inhibitors as a characteristic that could be exploited for treating SMARCA4-mutant cancer patients.

Deep analysis of acquired resistance to FGFR1 inhibitor identifies MET and AKT activation and an expansion of AKT1 mutant cells.

The development of acquired resistance (AR) to tyrosine kinase inhibitors (TKIs) of FGFR1 activation is currently not well understood. To gain a deeper insight into this matter in lung cancer, we used the FGFR1-amplified DMS114 cell line and generated multiple clones with AR to an FGFR1-TKI. We molecularly scrutinized the resistant cells, using whole-exome sequencing, RNA sequencing and global DNA methylation analysis. Our results show a de novo activation of AKT and ERK, and a reactivation of mTOR. Furthermore, the resistant cells exhibited strong upregulation and activation of MET, indicating crosstalk between the FGFR1 and MET axes. The resistant cells also underwent a global decrease in promoter hypermethylation of the CpG islands. Finally, we observed clonal expansion of a pre-existing change in AKT1, leading to S266L substitution, within the kinase domain of AKT. Our results demonstrate that AR to FGFR1-TKI involves deep molecular changes that promote the activation of MET and AKT, coupled with common gene expression and DNA methylation profiles. The expansion of a substitution at AKT1 was the only shared genetic change, and this may have contributed to the AR.

MET-Oncogenic and JAK2-Inactivating Alterations Are Independent Factors That Affect Regulation of PD-L1 Expression in Lung Cancer.

Purpose: The blockade of immune checkpoints such as PD-L1 and PD-1 is being exploited therapeutically in several types of malignancies. Here, we aimed to understand the contribution of the genetics of lung cancer to the ability of tumor cells to escape immunosurveillance checkpoints.Experimental Design: More than 150 primary non-small cell lung cancers, including pulmonary sarcomatoid carcinomas, were tested for levels of the HLA-I complex, PD-L1, tumor-infiltrating CD8+ lymphocytes, and alterations in main lung cancer genes. Correlations were validated in cancer cell lines using appropriate treatments to activate or inhibit selected pathways. We also performed RNA sequencing to assess changes in gene expression after these treatments.Results:MET-oncogenic activation tended to associate with positive PD-L1 immunostaining, whereas STK11 mutations were correlated with negative immunostaining. In MET-altered cancer cells, MET triggered a transcriptional increase of PD-L1 that was independent of the IFNγ-mediated JAK/STAT pathway. The activation of MET also upregulated other immunosuppressive genes (PDCD1LG2 and SOCS1) and transcripts involved in angiogenesis (VEGFA and NRP1) and in cell proliferation. We also report recurrent inactivating mutations in JAK2 that co-occur with alterations in MET and STK11, which prevented the induction of immunoresponse-related genes following treatment with IFNγ.Conclusions: We show that MET activation promotes the expression of several negative checkpoint regulators of the immunoresponse, including PD-L1. In addition, we report inactivation of JAK2 in lung cancer cells that prevented the response to IFNγ. These alterations are likely to facilitate tumor growth by enabling immune tolerance and may affect the response to immune checkpoint inhibitors. Clin Cancer Res; 24(18); 4579-87. ©2018 AACR.

Genomic and Molecular Screenings Identify Different Mechanisms for Acquired Resistance to MET Inhibitors in Lung Cancer Cells.

The development of resistance to tyrosine kinase inhibitors (TKI) limits the long-term efficacy of cancer treatments involving them. We aimed to understand the mechanisms that underlie acquired resistance (AR) to MET inhibitors in lung cancer. EBC1 cells, which have MET amplification and are sensitive to TKIs against MET, were used to generate multiple clones with AR to a MET-TKI. Whole-exome sequencing, RNA sequencing, and global DNA methylation analysis were used to scrutinize the genetic and molecular characteristics of the resistant cells. AR to the MET-TKI involved changes common to all resistant cells, that is, phenotypic modifications, specific changes in gene expression, and reactivation of AKT, ERK, and mTOR. The gene expression, global DNA methylation, and mutational profiles distinguished at least two groups of resistant cells. In one of these, the cells have acquired sensitivity to erlotinib, concomitantly with mutations of the KIRREL, HDAC11, HIATL1, and MAPK1IP1L genes, among others. In the other group, some cells have acquired inactivation of neurofibromatosis type 2 (NF2) concomitantly with strong overexpression of NRG1 and a mutational profile that includes changes in LMLN and TOMM34 Multiple independent and simultaneous strategies lead to AR to the MET-TKIs in lung cancer cells. The acquired sensitivity to erlotinib supports the known crosstalk between MET and the HER family of receptors. For the first time, we show inactivation of NF2 during acquisition of resistance to MET-TKI that may explain the refractoriness to erlotinib in these cells. Mol Cancer Ther; 16(7); 1366-76. ©2017 AACR.

Genomic Profiling of Patient-Derived Xenografts for Lung Cancer Identifies B2M Inactivation Impairing Immunorecognition.

Purpose: We aimed to maximize the performance of detecting genetic alterations in lung cancer using high-throughput sequencing for patient-derived xenografts (PDXs).Experimental Design: We undertook an integrated RNA and whole-exome sequencing of 14 PDXs. We focused on the genetic and functional analysis of ß2-microglobulin (B2M), a component of the HLA class-I complex.Results: We identified alterations in genes involved in various functions, such as B2M involved in immunosurveillance. We extended the mutational analysis of B2M to about 230 lung cancers. Five percent of the lung cancers carried somatic mutations, most of which impaired the correct formation of the HLA-I complex. We also report that genes such as CALR, PDIA3, and TAP1, which are involved in the maturation of the HLA-I complex, are altered in lung cancer. By gene expression microarrays, we observed that restitution of B2M in lung cancer cells upregulated targets of IFNα/IFNγ. Furthermore, one third of the lung cancers lacked the HLA-I complex, which was associated with lower cytotoxic CD8+ lymphocyte infiltration. The levels of B2M and HLA-I proteins correlated with those of PD-L1. Finally, a deficiency in HLA-I complex and CD8+ infiltration tended to correlate with reduced survival of patients with lung cancer treated with anti-PD-1/anti-PD-L1.Conclusions: Here, we report recurrent inactivation of B2M in lung cancer. These observations, coupled with the mutations found at CALR, PDIA3, and TAP1, and the downregulation of the HLA-I complex, indicate that an abnormal immunosurveillance axis contributes to lung cancer development. Finally, our observations suggest that an impaired HLA-I complex affects the response to anti-PD-1/anti-PD-L1 therapies. Clin Cancer Res; 23(12); 3203-13. ©2016 AACR.

MAX inactivation in small cell lung cancer disrupts MYC-SWI/SNF programs and is synthetic lethal with BRG1.

Our knowledge of small cell lung cancer (SCLC) genetics is still very limited, amplification of L-MYC, N-MYC, and C-MYC being some of the well-established gene alterations. Here, we report our discovery of tumor-specific inactivation of the MYC-associated factor X gene, MAX, in SCLC. MAX inactivation is mutually exclusive with alterations of MYC and BRG1, the latter coding for an ATPase of the switch/sucrose nonfermentable (SWI/SNF) complex. We demonstrate that BRG1 regulates the expression of MAX through direct recruitment to the MAX promoter, and that depletion of BRG1 strongly hinders cell growth, specifically in MAX-deficient cells, heralding a synthetic lethal interaction. Furthermore, MAX requires BRG1 to activate neuroendocrine transcriptional programs and to upregulate MYC targets, such as glycolysis-related genes. Finally, inactivation of the MAX dimerization protein, MGA, was also observed in both non-small cell lung cancer and SCLC. Our results provide evidence that an aberrant SWI/SNF-MYC network is essential for lung cancer development.

Determining the profiles and parameters for gene amplification testing of growth factor receptors in lung cancer.

Growth factor receptors (GFRs) are amenable to therapeutic intervention in cancer and it is important to select patients appropriately. One of the mechanisms for activation of GFRs is gene amplification (GA) but discrepancies arising from the difficulties associated with data interpretation and the lack of agreed parameters confound the comparison of results from different laboratories. Here, we attempt to establish appropriate conditions for standardization of the determination of GA in a panel of GFRs. A NSCLC tissue microarray panel containing 302 samples was screened for alterations at ALK, FGFR1, FGFR2, FGFR3, ERBB2, IGF1R, KIT, MET and PDGFRA by FISH, immunostaining and/or real-time quantitative RT-PCR. Strong amplification was found for FGFR1, ERBB2, KIT/PDFGRA and MET, with frequencies ranging from 1 to 6%. Thresholds for overexpression and GA were established. Strong immunostaining was found in most tumors with ERBB2, MET and KIT amplification, although some tumors underwent strong immunostaining in the absence of GA. KIT and PDFGRA were always coamplified, but only one tumor showed PDGFRA overexpression, indicating that KIT is the main target. Amplification of FGFR1 predominated in squamous cell carcinomas, although the association with overexpression was inconclusive. Interestingly, alterations at ALK, MET, EGFR, ERBB2 and KRAS correlated with augmented levels of phospho-S6 protein, suggesting activation of the mTOR pathway, which may prove useful to pre-select tumors for testing. Overall, here, we provide with parameters for the determination of GA at ERBB2, MET, KIT and PDGFRA which could be implemented in the clinic to stratify lung cancer patients for specific treatments.

Assessing the RNA effect of 26 DNA variants in the BRCA1 and BRCA2 genes.

Comprehensive genetic testing of the breast cancer susceptibility genes BRCA1 and BRCA2 identified approximately 16% of variants of unknown significance (VUS), a significant proportion of which could affect the correct splicing of the genes. Our aim is to establish a workflow for classifying VUS in these complex genes, the first stage of which is splicing analysis. We used a combined approach consisting of five in silico splicing prediction programs and RT-PCR analysis for a set of 26 variants not previously studied at the mRNA level and six variants that had already been studied, four of which were used as positive controls as they were found to affect the splicing of these genes and the other two were used as negative controls. We identified a splicing defect in 8 of the 26 newly studied variants and ruled out splicing alteration in the remaining 18 variants. The results for the four positive and the two negative control variants were consistent with results presented in the literature. Our results strongly suggest that the combination of RNA analysis and in silico programs is an important step towards the classification of VUS. The results revealed a very high correlation between experimental data and in silico programs when using tools for predicting acceptor/donor sites but a lower correlation in the case of tools for identifying ESE elements.

Massive parallel DNA pyrosequencing analysis of the tumor suppressor BRG1/SMARCA4 in lung primary tumors.

The tumor suppressor gene, SMARCA4 (or BRG1), which encodes the ATPase component of the chromatin remodeling complex SWI/SNF, is commonly inactivated by mutations and deletions in lung cancer cell lines. However, SMARCA4 alterations appear to be rare in lung primary tumors. Ultra-deep sequencing technologies provide a promising alternative to achieve a sensitivity superior to that of current sequencing strategies. Here we used ultra-deep pyrosequencing to screen for mutations over the entire SMARCA4 coding region in 12 lung tumors without detectable BRG1 protein. While automatic-fluorescence-based sequencing detected one somatic mutation (p.K586X), the pyrosequencing revealed additional variants, thus increasing the sensitivity. One of the variants, which affected a consensus splice site, was confirmed by individual cloning of PCR products, ruling out the possibility of PCR or pyrosequencing artifacts. This mutation, confirmed to be somatic, was present at a frequency of ten percent, suggesting normal cell contamination in the tumor. Our analysis also allowed us to determine the sensitivity and to identify some limitations of the technology. In conclusion, in addition to cell lines, SMARCA4 is biallelically inactivated in a significant proportion of lung primary tumors, thereby constituting one of the most important genes contributing to the development of this type of cancer.

Dissecting loss of heterozygosity (LOH) in neurofibromatosis type 1-associated neurofibromas: Importance of copy neutral LOH.

Dermal neurofibromas (dNFs) are benign tumors of the peripheral nervous system typically associated with Neurofibromatosis type 1 (NF1) patients. Genes controlling the integrity of the DNA are likely to influence the number of neurofibromas developed because dNFs are caused by somatic mutational inactivation of the NF1 gene, frequently evidenced by loss of heterozygosity (LOH). We performed a comprehensive analysis of the prevalence and mechanisms of LOH in dNFs. Our study included 518 dNFs from 113 patients. LOH was detected in 25% of the dNFs (N = 129). The most frequent mechanism causing LOH was mitotic recombination, which was observed in 62% of LOH-tumors (N = 80), and which does not reduce the number of NF1 gene copies. All events were generated by a single crossover located between the centromere and the NF1 gene, resulting in isodisomy of 17q. LOH due to the loss of the NF1 gene accounted for a 38% of dNFs with LOH (N = 49), with deletions ranging in size from ∼80 kb to ∼8 Mb within 17q. In one tumor we identified the first example of a neurofibroma-associated second-hit type-2 NF1 deletion. Analysis of the prevalence of mechanisms causing LOH in dNFs in individual patients (possibly under genetic control) will elucidate whether there exist interindividual variation.

Modulation of aberrant NF1 pre-mRNA splicing by kinetin treatment.

Neurofibromatosis type 1 is one of the most common neurocutaneous autosomal dominant disorders. It is caused by mutations in the neurofibromatosis type 1 (NF1) gene and approximately 30-40% of them affect the correct splicing of NF1 pre-mRNA. In this report, we evaluate the effect of five different drugs, previously found to modify splicing in several genetic disorders, on the splicing of mutated NF1 alleles. For this purpose, cell lines derived from patients bearing 19 different NF1-splicing defects were used. Our results showed that kinetin partially corrects the splicing defect in four of the studied mutations (c.910C>T, c.3113G>A, c.6724C>T and c.6791dupA). Our study is a valuable contribution to the field because it identifies new exon-skipping events that can be reversed by kinetin treatment and provides new information about kinetin splicing modulation. However, owing to the nature of mutations in our patients, kinetin treatment could not be used as a therapeutic agent in these cases.

Antisense therapeutics for neurofibromatosis type 1 caused by deep intronic mutations.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder affecting 1:3,500 individuals. Disease expression is highly variable and complications are diverse. However, currently there is no specific treatment for the disease. NF1 is caused by mutations in the NF1 gene, approximately 2.1% of constitutional mutations identified in our population are deep intronic mutations producing the insertion of a cryptic exon into the mature mRNA. We used antisense morpholino oligomers (AMOs) to restore normal splicing in primary fibroblast and lymphocyte cell lines derived from six NF1 patients bearing three deep intronic mutations in the NF1 gene (c.288+2025T>G, c.5749+332A>G, and c.7908-321C>G). AMOs were designed to target the newly created 5' splice sites to prevent the incorporation of cryptic exons. Our results demonstrate that AMO treatment effectively restored normal NF1 splicing at the mRNA level for the three mutations studied in the different cell lines analyzed. We also found that AMOs had a rapid effect that lasted for several days, acting in a sequence-specific manner and interfering with the splicing mechanism. Finally, to test whether the correction of aberrant NF1 splicing also restored neurofibromin function to wild-type levels, we measured the amount of Ras-GTP after AMO treatment in primary fibroblasts. The results clearly show an AMO-dependent decrease in Ras-GTP levels, which is consistent with the restoration of neurofibromin function. To our knowledge this is the first time that an antisense technique has been used successfully to correct NF1 mutations opening the possibility of a therapeutic strategy for this type of mutation not only for NF1 but for other genetic disorders.

Nature and mRNA effect of 282 different NF1 point mutations: focus on splicing alterations.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant genetic disorder caused by mutations in the NF1 gene. In this paper we report our experience using the cDNA-SSCP/HD analysis as a mutational screening approach and the double characterization of all mutations at the DNA and RNA levels. Two hundred and eighty-two different mutations (in 374 independent patients) were identified, 140 of which were novel in our population. Most of these mutations are unique and distributed along the gene. However, we also detected 37 recurrent mutations. Our approach is limited with respect to the detection of single base substitutions, but it is highly effective in the detection of frameshift mutations and mutations that affect the correct splicing. Due to this bias we focus here in the characterization of these two types of mutations. Forty-seven percent of mutations found were frameshift mutations, with small deletions being 2.3 times more common than small insertions. At the mRNA level, 44% of mutations affected the correct splicing, 80% of them located in the consensus sequences, with the donor site being much more frequently involved. The remaining 20% consisted of mutations located in deep intronic sites and mutations located in the coding region. In general the latter group produces different types of mutated transcripts with specific proportions for each mutation. The double characterization of mutations at the DNA and RNA levels enables to detect a broader spectrum of mutations than any single level approach, and provides a greater understanding of their molecular pathogenesis.

Tumor LOH analysis provides reliable linkage information for prenatal genetic testing of sporadic NF1 patients.

The neurofibromatosis type 1 gene has one of the highest mutation rates in humans: about 50% of NF1 patients are de novo cases. Although direct mutation characterization has greatly improved over the past decade, in the context of clinical genetics services worldwide, there is still a significant number of patients for which, while fulfilling NF1 clinical criteria, no constitutive mutation is found at a desired time. This is particularly critical for prenatal genetic testing of sporadic cases. Here we describe the use of loss of heterozygosity information in neurofibromas to obtain linkage information on the affected NF1 haplotype, which may be applied for prenatal testing in sporadic patients. However, proper genetic counseling should be provided regarding the possibility of somatic mosaicism.

NF1 mutation rather than individual genetic variability is the main determinant of the NF1-transcriptional profile of mutations affecting splicing.

A significant number of neurofibromatosis type 1 (NF1) mutations result in exon skipping. The majority of these mutations do not occur in the canonical splice sites and can produce different aberrant transcripts whose proportions have not been well studied. It has been hypothesized that differences in the mutation-determined NF1-transcriptional profile could partially explain disease variability among patients bearing the same NF1 splice defect. In order to gain insight into these aspects, we analyzed the proportion of the different transcripts generated by nine NF1-splicing mutations in 30 patients. We assessed the influence of the mutation in the NF1-related transcriptional profiles and investigated the existence of individual differences in a global manner. We analyzed potential differences in tissue-specific transcriptional profiles and evaluated the influence of sample processing and mRNA nonsense-mediated decay (NMD). Small transcriptional differences were found in neurofibromas and neurofibroma-derived Schwann cells (SC) compared to blood. We also detected a higher cell culture-dependent NMD. We observed that mutation per se explains 93.5% of the profile variability among mutations studied. However, despite the importance of mutation in determining the proportion of NF1 transcripts generated, we found certain variability among patients with the same mutation. From our results, it seems that genetic factors influencing RNA processing play a minor role in determining the NF1-transcriptional profile. Nevertheless neurofibromin studies would clarify whether these small differences translate into significant functional changes that could explain the great clinical expressivity observed in the disease or any of the disease-related traits.