MM is still a relatively rare disease with extremely low incidence. However, once it occurs, its consequences are unimaginable. At present, there are still no definite prognostic factors and treatment options for MM, and the pathogenesis of MM is not well understood. As malignant progression is quite rare in meningiomas, few malignant cases were analyzed. The lack of widely accepted objective grading criteria has further hindered progress in the field of meningioma biology. We can only use large databases to analyze its clinical characteristics, predict prognostic factors, and gradually deduce the possible molecular mechanism and phenotype of MM through other grades of meningioma, so as to provide new methods and basis for subsequent treatment. According to the results of our research team, the patient's gender, age, stage and chemotherapy are the factors that significantly affect the prognosis. Because the sample size of chemotherapy population is small, accounting for only 6% of the total population, and chemotherapy is not a routinely recommended method for the treatment of MM, strictly, chemotherapy is not a prognostic factor for MM.
In our study, we found that surgical resection had no significant benefit on the survival of patients, and no matter what surgical resection method was performed, the survival of patients was not effectively prolonged. Postoperative radiotherapy may be an effective prognostic factor, but the results were not statistically significant when included in the COX multivariate regression. Studies have shown that postoperative conventional radiotherapy is an effective treatment[9] for most benign and anaplastic meningiomas. However, for higher grade meningiomas such as MM, postoperative radiotherapy often does not show its due advantages[10]. Therefore, considering the side effects and efficacy of brain radiotherapy, the radiation therapy for MM should be more conservative. As for chemotherapy, there is even a negative impact on patient survival. Many chemotherapeutic agents have been used to treat meningiomas with very limited effects, such as treatment with the chemotherapeutic agent temozolomide, which only slightly improved survival[11]. However, there is evidence in the literature that some case series using chemotherapy for MM have investigated the role of hydroxyurea, imatinib, somatostatin analogues, and angiogenesis inhibitors. Hydroxyurea and imatinib have had limited efficacy. In contrast, angiogenesis inhibitors may play a role in the treatment of MM.
In our study, gender and age were two more significant influencing factors. Many literatures have shown that age and gender may be independent prognostic factors for different grades and types of meningiomas, and they are closely related[12]-[13]. Therefore, we speculate that this may be related to the patient's own hormone levels or the expression of related receptors or genes. In addition, many studies and statistics have shown that gender is a characteristic factor of meningiomas. In low-grade meningiomas, women are more common, while high-grade meningiomas are more [14]-[15]common in men. It has been further demonstrated that meningiomas express female hormone receptors, such as estrogen receptor (ER) and progesterone receptor [16](PR), but their relationship with female hormone receptors has not been studied according to the classification of meningiomas. Brian et al. showed a moderately elevated risk of meningioma in women who had experienced breast cancer and a moderately elevated [17]risk of breast cancer in women who had experienced meningioma. This suggests that the possible molecular phenotypes between breast cancer and meningioma may be common or interact with each other, and hormones or their receptors may be an important link, but further studies are needed to prove it.
The treatment of MM is limited and the prognosis is poor. Therefore, the analysis of clinical characteristics of MM can reflect the characteristics and prognosis of RM to a certain extent, which provides strong help for this study to explore problems from clinical data. In order to solve the problem of limited treatment methods of RM, based on other existing research results at home and abroad, this study started from the direction of targeted therapy, took advantage of the characteristics of RM mainly distributed in WHO grade Ⅲ and WHO grade Ⅱ, and used the gene dataset of public database to analyze the differential genes between WHO grade of meningioma. This study will provide new evidence and direction for the diagnosis and treatment of RM.
To explore the functions of these genes and the relationships among them, we further explored the potential associations and research frontiers of these genes. Epidermal growth factor receptor (EGFR, also known as ErbB1 or HER1) and Erb-B2 receptor tyrosine kinase 3 (ErbB3, also known as HER3) both belong to the human epidermal growth factor receptor (HER) family, which belongs to the ErbB family. It also includes two other members ErbB2 / HER2 and ErbB4 / HER4. Among them, EGFR is a transmembrane receptor tyrosine kinase (RTK), which exists as a monomer on the cell surface in a compact self-inhibitory state and shows minimal kinase activity. It contributes to a large number of cellular functions, including cell survival, proliferation, adhesion and differentiation as well as other pathophysiological processes [18]. EGFR can also serve as a major cargo of small extracellular vesicles (SEVs), participating in the reprogramming of recipient cells along with co-expressed proteins and small Rnas, contributing to influence immunity, premetastatic niche preparation, angiogenesis, cancer cell stemness, and horizontal oncogene transfer [19]. At present, EGFR-tyrosine kinase inhibitors (TKI) are considered as the standard first-line treatment for some malignant tumors with EGFR mutations, especially non-small cell lung cancer (NSCLC). The first-generation (gefitinib, erlotinib), second-generation (afatinib), and third-generation (osimertinib) TKI have all achieved varying degrees of efficacy and results[19]. Several studies have shown that EGFR is overexpressed and activated in human meningiomas, and the high level of ligands also supports the involvement of this growth factor receptor system in meningiomas tumorigenesis. Therefore, EGFR may be a potential candidate for targeted therapy of meningiomas [20]. By GEO database analysis, EGFR was positively correlated with WHO grade (Table 2), but EGFR seemed to be more likely to be activated in WHO grade II meningiomas (Fig 6). It has been shown that the percentage staining score for EGFR expression is higher in benign and atypical tumors, but lower in all malignant tumor samples evaluated [21]; Using immunohistochemistry and fluorescence in situ hybridization (FISH) for gene amplification, some analyses have shown that a rise in EGFR protein content is associated with progression from benign to atypical or anaplastic meningiomas, so that EGFR immunostaining correlates directly with tumor grade. In contrast, EGFR expression was not associated with survival overall or survival free of relapse. The findings suggest that EGFR may not be a prognostic marker for patient outcomes, but is a marker of tumor progression [22], which seems to corroborate the results of the present study.
Preliminary analyses in this study identified ErbB3 as a potential target gene for meningiomas and showed a strong inverse correlation with the WHO grade of meningiomas (Table 4). Therefore, the function and mechanism of ErbB3 are essential for our study of the pathogenesis and malignant transformation of meningiomas. As for ErbB3, it often does not function independently, but collaborates with other proteins. As part of signal transduction, ErbB3 forms dimers with other receptors and is phosphorylated by partners, of which HER2 is one of the most important [23].The PI-3K/Akt pathway is well-known for its role in normal development and tumorigenesis, and ErbB3 is best suited for activating this pathway[24]. At the same time, some studies have also found that the increased expression of ErbB3 can be observed in a variety of cancer samples, and is associated with poor survival of cancer patients. Investigations into the underlying mechanisms suggest that ErbB3 expression is a major cause of cancer treatment failure. Activation of ErbB3 signaling has also been shown to promote cancer metastasis [25]. According to much evidence, ErbB3 often interacted with other RTKS to form heterodimeric complexes that activated oncogenic signaling, and PI-3K/Akt pathway and Src kinase play key roles in cancer cell survival, proliferation, and progression [26]-[27]. Therefore, the expression of ErbB3 is very important for tumorigenesis and development. Cancers such as colorectal cancer, gastric cancer, breast cancer, melanoma, ovarian cancer, head and neck cancer, pancreatic cancer, and cervical cancer contain its traces[28], and the expression of ErbB3 also shows differences in meningioma. In a study examining 186 primary meningiomas, Most tumor samples of all grades were highly expressed for ErbB3 and ErbB4, two members of the ErbB RTK family. In contrast, normal meningeal tissues showed no immunoreactivity, suggesting the potential diagnostic markers [29]. Violin plot analysis of a dataset of 42 invasive meningioma tumor samples revealed overall similar gene expression across the different ErbB receptor family members, compared with all other members of the ErbB receptor family, Higher levels of ErbB2 (HER2) and ErbB3 (HER3) gene expression have been observed in meningioma patients [30]. "This is in line with the present study to some extent, as ErbB3 is more likely to be expressed in low-grade meningiomas, especially in WHO grade I, and is not significantly distributed in WHO grade II and III meningiomas, and may even show a low expression tendency." This fully indicates the potential of ErbB3 as a target gene, but whether ErbB3 in meningiomas, especially in low-grade meningiomas, has the same mechanism of development as other meningiomas still deserves further investigation.
Progesterone is well known for its reproductive function in women and is produced by the corpus luteum during the luteal phase of the menstrual cycle. During pregnancy, progesterone is mainly synthesized by the placenta [31]. Adrenal gland is another important site for progesterone synthesis and is the main source of circulating progesterone in men [32]. Free progesterone easily crosses the Blood-brain barrier (BBB) and diffuses in the nerve parenchyma [33]. In addition, they interact with the endothelial cells of capillaries through their endfeet, helping to control the BBB and regulate blood flow in the CNS [34]. A ligand-dependent transcription factor, the progesterone receptor (PR) is found mainly in female reproductive tissues and in the central nervous system. In response to binding to its cognate steroid hormone, progesterone, PR regulates the expression of gene networks to control the development, differentiation and proliferation of target tissues and the pathological process of endocrine cancers[35]. There is evidence that the interaction of progesterone with the membrane progesterone receptor may produce immunomodulatory proteins, such as progestin-induced blocking factor (PIBF), which may be required by the fetoplacental unit to aid in immunosuppression by controlling cell populations and subsequent cytokine production, thereby aiding proliferation, invasion and, perhaps most importantly, evasion of immune surveillance [36], However, there are few reports on the mechanisms of other tumor development, especially those related to meningioma, and the same is also the case in the distribution of proteins. PR-A and PR-B, which are both transcribed from a single gene, are highly expressed not only in brain regions associated with reproduction, but also in regions important for cognitive function and emotional processing. In the central nervous system, PR is distributed in the hypothalamus, amygdala, hippocampus, thalamus and frontal cortex [37]. It seems that we do not see significant PR expression in meningeal tissues, which is similar to the trend of PR expression obtained in our study: PR expression is only slightly up-regulated or not up-regulated in WHO grade I meningiomas, and its expression is more significantly up-regulated in WHO grade II and III meningiomas.
From the immunohistochemical results of the pathological specimens, we can see intuitively that the prediction of the two hub genes was in line with the results of the previous database analysis: EGFR was positively correlated with WHO grade, while ErbB3 was negatively correlated with WHO grade. Coincidentally, the two key hub genes we obtained belong to the human epidermal growth factor receptor family. It is not difficult to speculate that they may play a key role in the malignant process of meningioma, and their existence and regulation pathways may also be the key pathways in the pathogenesis and development of meningioma. Meningioma tumors and cell lysates contain high levels of phosphorylated epidermal growth factor receptor (pEGFR) compared with non-tumor control tissues. EGFR-mediated signaling mediates aberrant STAT1 activation, and EGFR inhibition impairs cell proliferation and decreases the levels of cyclin D1, phosphorylated AKT, and phosphorylated extracellular signal-regulated kinase (ERK) 1/2 [38]. In addition, some new research evidence shows that EGFR is not only distributed in meningioma tissues, but also shows a certain degree of difference between WHO grades. An analysis of gene amplification using immunohistochemistry and fluorescence in situ hybridization (FISH) showed that an increase in EGFR protein content was associated with the progression from benign to atypical or anaplastic meningiomas; thus, EGFR immunostaining correlated directly with tumor grade, whereas EGFR expression did not correlate with overall or relapse-free survival. Based on these findings, EGFR may be a marker of tumor progression, but not a prognostic marker [39].
An important aspect of EGFR regulation is associated with alterations in its protein turnover and subcellular distribution. Nuclear epidermal growth factor receptor (nEGFR) localization in cancer cells including non-small cell lung cancer (NSCLC) has been described to promote survival through kinase-independent interactions as a nuclear kinase or co-transcriptional activator [40]. Several solid tumors have been investigated for the relationship between nEGFR and cancer prognosis. The first evidence that high levels of nEGFR are associated with poorer OS in breast cancer patients was published by Lo et al. in 2005[41]. A similar outcome was observed in NSCLC, where nEGFR enhanced resistance to EGFR-targeted therapy, chemotherapy, and radiation[42]. However, in this study, no significant correlation between nEGFR and WHO grade or recurrence of meningioma was observed.
Similarly, we found a similar pattern in ErbB3, a member of the ErbB family.In a study of 186 primary meningiomas of all grades, ErbB3 was highly expressed both in the cytoplasm and in the cell membrane of most tumor samples. In contrast, non-neoplastic meningeal tissue showed no immunoreactivity, suggesting the presence of potential diagnostic markers [43]. In addition, a violin plot analysis was performed on a dataset of 42 invasive meningioma tumor samples. Although the analysis revealed overall similar gene expression across different ErbB receptor family members, higher levels of ErbB2 (HER2) and ErbB3 (HER3) gene expression were observed in meningioma patients compared to all other members of the ErbB receptor family [44]. However, these studies do not indicate a trend relationship between ErbB3 and WHO grade, and the relevant studies are also less reported. The present study suggests that although there may be a negative correlation between ErbB3 and WHO grade, the protein distribution of ErbB3 tends to be more frequent in WHO grade Ⅰ meningiomas and may be used as a potential diagnostic marker for benign meningiomas.
At present, the hormone dependence of meningiomas has been confirmed based on the results of several epidemiological investigations and clinical characteristics studies [45], which is also consistent with the results discussed in Chapter 1 of this study. But it needs special discussion that the effects of progesterone in the female reproductive system are thought to be mainly mediated by the nuclear progesterone receptor (nPR). The physiological relevance of membrane progesterone receptors (MPRS) is unclear because their ability to bind progesterone is relatively low compared to nPR, and some studies have shown that they are not activated by progesterone [46]; Some studies have further explored the role of mPR in the nervous system, and the results suggest that mPR may be a mediator of the various effects of natural and synthetic neurosteroids in the brain [47]. Therefore, the study of nPR was also included in the evaluation of immunohistochemical results in the present study. The results also showed that the correlation between nPR and meningioma grade and recurrence was indeed statistically significant, while the results of PR were negative . In addition, there was an association between meningiomas and breast cancer. The estimated risk of breast cancer after a diagnosis of meningioma was 1.54 (95% confidence interval [95%CI], 0.77 to 2.75) and the risk of meningioma after a diagnosis of breast cancer was 1.40 (95%CI, 0.67 to 2.58)[12]. A recent study reported that more than 90% of meningiomas express PR[48]. A higher PR expression is associated with a better prognosis and a lower recurrence risk[49], and a correlation exists between PR expression and WHO grade meningiomas, with higher PR expression in grade 1 tumors, lower PR expression in grade 2, and very low PR expression in grade 3.[50]. Estrogen and its receptors are rarely reported in meningiomas, and some studies have conflicting results. Some studies have suggested that ER expression in meningiomas may be associated with adverse prognosis [51], but this study has classified rhabdoid and papillary meningiomas as WHO grade II meningiomas since 2021, as the WHO grading guidelines for meningiomas remain the same. Therefore, the results of this part of the study are not accurate for the distribution of ER among different grades of meningiomas.
The present study suggests that the distribution of ER in different WHO grades of meningiomas is indeed different, and may be related to the progression of meningiomas to RM. However, the specific role of estrogen in this process remains to be further explored.
Hormone therapy for meningiomas is still controversial. For progesterone agonists, especially cyproterone acetate (CPA), which is associated with meningioma growth, regression or stabilization of meningiomas has been reported after cessation of treatment; Increasing evidence suggests an association between CPA use and the development of meningiomas. CPA over 10 mg/day is even restricted by the European Medicines Agency due to the risk of meningioma[52]. It may also indicate that meningiomas are hormone-dependent, and that this dependence is often done through hormone receptors. However, according to our results, this dependence may be mainly observed in low-grade meningiomas. Some in vitro studies showed that estradiol either stimulated the growth of meningioma cells or had no significant effect. "Similarly, tamoxifen, a selective ER modulator with tissue-specific estrogenic and antiestrogenic activities, has been shown to stimulate, ineffective, or inhibit meningioma cells in culture." Therefore, the current hormone therapy for meningiomas, especially RM, still has not achieved good results. It can be bold to guess that the role of hormone receptors in meningioma may be to promote the progression of meningioma to malignant, refractory and relapsing direction. Once the progress is completed, hormones and their related receptors may no longer play a similar role. Therefore, anti-hormone or anti-hormone receptor therapy can not improve the prognosis of RM patients. Of course, this is only a conjecture on paper at the current research stage, and more convincing basic research is needed to further explore the role of hormones and their related receptors in RM.
In conclusion, EGFR and ErbB3, nPR and ER all showed differential distribution in the WHO grade of meningiomas, and statistically significant differences in the subgroups of recurrent and non-recurrent meningiomas. This study has certain guiding significance for the diagnosis and treatment of RM, and also provides some research ideas and directions for the future research of RM.
Based on the analysis of clinical characteristics and prognosis of RM in SEER database, combined with gene difference and co-expression analysis in some gene databases, and the verification of pathological specimens in a single center database, we can initially conclude the following conclusions: RM has a poor prognosis and limited treatment methods. At present, no conventional treatment such as surgery, radiotherapy and chemotherapy has a good effect on it. EGFR, nEGFR and ErbB3 are differentially expressed in different grades of meningiomas, among which EGFR tends to be highly expressed in high-grade meningiomas, and ErbB3 tends to be highly expressed in low-grade meningiomas, but their effect on tumor recurrence may be small. This suggests that both of them may be potential biomarkers for RM diagnosis and treatment. In terms of the conclusion of the current research on hormone receptors ER, PR and nPR, the research on PR is lack of statistical significance, and the hormone therapy and targeted therapy related to PR have not achieved consistent good efficacy, but ER and nPR are significantly correlated with WHO grade and recurrence of meningioma, so ER and nPR have the potential to be used as the diagnosis and treatment targets of RM.