Intracranial tumors in children are not the comparable with those of adults, and also have obvious differences in terms of topographical distribution, pathological types, treatment, prognosis, and outcome. Consistent with the vast majority of other studies in the Asian region(Ahmed et al. 2007, Cho et al. 2002, Makino et al. 2010, Wong et al. 2005), our study also revealed a predominance of boys with intracranial tumors, with a sex ratio of 1.41:1, which was slightly higher than that in Western countries(Bauchet et al. 2009, El-Gaidi 2011, Hjalmars et al. 1999). Tumors at different life stages reflect different dynamics and biological behaviors(Rickert & Paulus 2001). In our study, the mean age of the affected children was 8.8, which is similar to the results of studies in Iran and Pakistan(Ahmed et al. 2007, Mehrazin & Yavari 2007). Our study suggested that the number of patients increased steadily with age and peaked at the age of 10–15 years. This phenomenon was also reported in a study conducted at the Beijing Neurosurgical Institute, Beijing, China(Zhou et al. 2008), and the findings were corroborated by studies in England, Sweden, and India(C et al. 2016, Govindan et al. 2018, Stiller et al. 2019). Conversely, some studies have suggested that the highest incidence occurs in the 5–9-year age group(Cho et al. 2002, Makino et al. 2010, Riaz et al. 2019). We speculated that this may be caused by the shyness of children in western China to express their symptoms, and when they grow up, they are more able to complain about their headache, visual disturbances, or endocrinopathies such as increased thirst or urination.
Regardless of tumor location, intracranial hypertension (53.9%) and ocular symptoms (11.7%) were the main clinical manifestations in our cohort of patients. However, our study also highlighted several other symptoms that indicate the possibility of developing tumors, such as weight loss, behavioral changes, school difficulties, developmental delay, head tilt, macrocephaly, diabetes insipidus, abnormal menstruation, and growth arrest. Furthermore, we were also concerned about the fact that 81 patients (9.1%) were asymptomatic before diagnosis. Hence, improving the comprehensive examination of children and raising awareness of the various complex and atypical symptoms of brain tumors in children will help in diagnosing the tumor and in alleviating the suffering of the child expeditiously.
In this study, we followed the WHO Classification of Central Nervous System Tumors 2016 for the diagnosis of different tumors. As for the most common intracranial tumors in children, most studies have reported that astrocytoma followed by medulloblastoma are the two most common intracranial tumors(Aghadiuno et al. 1985, El-Gaidi 2011, Katchy et al. 2013, King et al. 2015, Lannering et al. 2009, Ogun et al. 2016, QT et al. 2020, Rickert & Paulus 2001, Shanmugavadivel et al. 2020, Udaka & Packer 2018). However, some studies have reported medulloblastomas to be the most common pediatric intracranial tumors ahead of astrocytomas(Almutrafi et al. 2020, Govindan et al. 2018, Kadri et al. 2005, Nasir et al. 2010, Shah et al. 2015). According to the present study, astrocytomas with a frequency of 16.9% were the most common brain tumors, with the average age of onset of this tumor being 8.5 years. Among the 110 patients, there was a slight male predominance, with a ratio of 1.2:1, and there was no specific location preference. Obviously, most astrocytomas belong to low grade tumors, which is consistent with previous research(El-Gaidi 2011, Riaz et al. 2019, Shah et al. 2015). Medulloblastoma, an embryonal tumor of the posterior fossa, comprises up to 20% of all pediatric brain tumors(Ostrom et al. 2019, Shtil 2016). In our study, medulloblastoma was the second most common brain tumor, accounting for 13.5% of all brain tumors with a male predominance (ratio of 1.8). It has two incidence peaks in patients aged 4–5 years (18%) and in patients aged 7–8 years (23.8%) with a mean age of 7.8 years, which is slightly different from previous studies(Udaka & Packer 2018) but consistent with the study in China(Zhou et al. 2008). Craniopharyngioma is a benign epithelial tumor with slow growth that accounts for approximately 5–10% of pediatric brain tumors(Garre & Cama 2007, Muller et al. 2019). In this study, craniopharyngioma, the third most common, had a mean age of onset of 8.7 years and no discrepancy in incidence between sexes. Moreover, the critical location of the lesion and the difficulty in treating postoperative complications make the prognosis of patients generally poor(Muller et al. 2006). In our follow-up results of the 83 pediatric craniopharyngioma patients in our study, 10 patients died and 18 relapsed. Ependymomas are the fourth most common type, accounting for 6.3% of all pediatric brain tumors with a mean age of 6.9 years, consistent with some studies in Asia and Europe(C et al. 2016, El-Gaidi 2011, Makino et al. 2010, Zhou et al. 2008). Our study showed that there was a subtentorial predominance with a ratio of 1.56:1 and a slightly male predominance, with a ratio of 1.16:1. Germinoma, which accounts for 5.8% of all brain tumors in children, is the fifth most common, consistent with the consensus(Fetcko & Dey 2018).
Consistent with previous studies(Riaz et al. 2019), pilocytic astrocytomas were the most common childhood brain tumor subtypes in the present study. Studies have shown that pilocytic astrocytoma is associated with high levels of myeloid and lymphocyte infiltration and activation marker expression(Forsyth et al. 1993, Huang et al. 2005, Rosemberg & Fujiwara 2005). Therefore, it is inferred that immune cells are related to the occurrence and development of pilocytic astrocytomas. Based on the incidence rate of this type of tumor and the current treatment methods that are still not perfect, we decided to carry out bioinformatics analysis to provide theoretical guidance for further research.
In the present study, by analyzing the GEO44971 dataset, we identified 3264 DEGs in the tumor tissue. We then performed GO, DO, and GSEA analyses to explore the biological functions of the DEGs. The results showed that DEGs participated in the functions of neurotransmitter transfer and transmembrane transport, and are highly associated with lung disease, periodontal disease, skin disease, and obesity, and markedly enriched in neuroactive ligand receptor interaction, olfactory transduction, basal cell carcinoma, hedgehog signaling pathyway, and taste transduction KEGG pathways. Notably, immune-related functional items were found in the GO-BP pathway. These results suggest that DEGs were highly correlated with the immune system, which confirms our hypothesis.
DNA methylation causes transcriptional silencing to regulate gene expression. Therefore, we carried out methylation analysis on the GSE44864 dataset to determine whether methylation affects gene expression in pilocytic astrocytoma, and further precise exploration of differential genes. The results showed that methylation had the greatest effect on the expression of chromosome 17. The results of methylation site analysis were correlated with the gene expression of corresponding samples, and 45 genes with negative regulation of promoter methylation level and gene expression level were screened out. Therefore, the differential expression of some differential genes may be due to differential methylation of their own genes.
To screen the hub genes among these 45 differentially expressed genes, we used LASSO regression and the SVM-RFE algorithm. At the intersection of the two algorithms, we obtained five hub genes: NCKAP1L, GPR37L1, CSPG4, PPFIA4, and C8orf46, and their efficiency was also confirmed by the ROC curve.
In recent years, an increasing number of studies have focused on TME, in which immune cells and stromal cells play an important role in the diagnosis and prognosis of tumors(Hanahan & Coussens 2012). Therefore, we first performed ssGSEA analysis on the GSE44971 dataset. We found that compared with the normal group, the PA tumor group had a higher proportion of immune gene sets, except for activated CD4 T cells and effector memory CD4 T cells. This result suggests that we should perform further immunological analysis of the five hub genes. Then, using the ESTIMATE algorithm, we found that the high and low expression groups of NCKAP1L gene had significant differences in the immune, stromal, and estimate scores. Consequently, we further evaluated the correlation between the expression of NCKAP1L and immune gene sets, and found that this gene was positively correlated with all immune gene sets, especially in macrophages.
Our study is the first to report the relationship between NCKAP1L and PA. NCKAP1L, or Nck-associated protein 1-like, is a key component of the actin cytoskeleton machinery. The protein encoded by this protein is hematopoietic protein-1 (HEM-1), a hematopoietic lineage-restricted member of the Nap1l subunit of the WAVE (WASP-family verprolin-homologous protein) complex(Weiner et al. 2006). The role of this gene in tumors has not been extensively studied. Recently, it has been found that this gene plays an important role in the activation, migration, and cell contact formation of lymphoid and myeloid cells, including the formation of immune synapses in effector cells(Park et al. 2008). Subsequently, a few studies have revealed that it is associated with immunodeficiency, lymphoproliferation, and high inflammation, and may be a biomarker of some tumors(CN et al. 2020, M et al. 2020, Y et al. 2020). Similarly, our study also found that as a hub gene of PA, NCKAP1L plays an important role in the immune system. It is closely related to B cells and macrophages and may affect the TME in this way, thereby affecting the development of PA. Therefore, we provide a new basis and direction for the pathogenesis of PA and the study of the TME.
G protein-coupled receptor 37-like 1 (GPR37L1) and chondroitin sulfate proteoglycan 4 (CSPG4) have been shown to be expressed in astrocytomas and gliomas. GPR37L1 interacts with patched 1 (Ptch1) in the peri-ciliary membranes of astrocytes(La Sala et al. 2020), while CSPG4, a type I transmembrane protein, plays a role in the origin, progression, and angiogenesis of glioma(Mellai et al. 2020). Both these genes play a role in TME and may be promising as biomarkers for detecting PA progression and patient survival(Mellai et al. 2020). PPFIA4, also known as LIP.1 or Liprin alpha1, encodes liprin, which is related to neural signal transmission. Previous studies have shown that it is correlated with pancreatic cancer and small cell lung cancer(BA et al. 2009). Our study found that it may be one of the characteristic biomarkers of PA, and further research is needed to explore its role in tumor development and its relationship with TME. Chromosome 8 open reading frame 46 (C8orf46), a human protein-coding gene, has been named Vexin. Previous studies have suggested that Vexin is involved in embryonic neurogenesis and is related to cancer progression, but its function has not yet been elucidated clearly (Koshimizu et al. 2020, Moore et al. 2018). Our study is the first to report that this gene is associated with PA, which provides a new direction for future research.