CD44, a cell surface marker, is structurally integrated with merlin protein in the cell membrane of meningioma tumors, and its overexpression may be associated with the invasiveness and anaplasia of meningioma. It is a marker that could be used to facilitate histological detection and assist in brain brain-invasive growth of meningioma. However, there is a dearth of data available that shows the clinical impact of CD44 in meningioma. Therefore, the present study sought to explore the clinical impact of CD44 on meningioma patients.

We examined the correlation between CD44 protein expression with clinicopathological variables and the survival of patients. In addition, we determined the impact of CD44 in relation to treatment offered to patients with disease outcomes. Using ROC curves validated the efficacy of CD44 that discriminates the high and low-risk patients that develop recurrence and death during 48 months. Using immunohistochemistry the protein expression of CD44 was investigated. Our study illustrated CD44 as a significant independent marker for meningioma patients that could be able to identify high-risk meningioma patients. Strong expression of CD44 showed a positive association with WHO high-grade tumors and the presence of brain invasion. Also, in multivariate survival analysis, we showed that only CD44 remained the most potentially significant prognostic factor to predict reduced PFS and shorter OS. As per our knowledge, for the first time, our study showed the impact of CD44 in relation to treatment offered to meningioma patients, where we found that patients with strong CD44 protein expression had a significantly lower incidence of recurrence and death rate if they were treated with surgery only than if patients treated with surgery followed by adjuvant therapy. Thus, CD44 might be helpful to prevent patients from unnecessary overtreatment and thereby prevent them from drug-induced toxicity.

In the existing study, the majority of patients were female in gender, and that was higher than males, with female: male ratio found was 2:1. Out of 70 patients, 65.7% of patients were females. Meningioma is the only cerebral tumor whose predominance is female with a sex ratio estimated at 2:1 [10]. This figure was similar to that reported by Mostfa and Khairy [11] and Gassoum et al. [12] where females constituted 61.9% of their patients with a female: male ratio of 1.6:1. The association between hormone receptor expression and meningiomas has been used to explain the discordant prevalence of meningiomas in females, where the overall ratio is 2:1 in the brain [13, 14].

There has long been an association between hormone receptors expressed on meningiomas and their increased frequency among female patients, although the data has been highly variable. Pregnancy may be responsible for the sudden clinical onset of intracranial meningiomas because of the hormone-related tumor changes. Contraceptive and fertilization therapies, mainly with progesterone, should be avoided in patients with known meningiomas because of the risk of symptom occurrence and tumor progression [15]. On the contrary, Korhonen et al. [16] reported the higher incidence of meningiomas in women cannot be explained by differences in sex hormone receptors. In one meta-analysis, Benson et al. [17], reported significantly increased risk for all CNS tumors, including glioma and meningioma in users of estrogen-only as hormonal therapy. However, women taking estrogen-progestin therapy showed no increase in risk. Recently, Agopiantz et al. [18] have shown that progesterone receptors are currently the strongest parameter that has a role in meningioma development in females, however, the data on estrogen and androgen receptors are still patchy and require further study. Thus, the high incidence of meningioma in women cannot be explained only by differences in sex hormone receptors and thus other hidden causes should be looked for.

CD44 is a transmembrane protein, so the delocalization of CD44 to the cytoplasm may cause alterations in the cell–cell and cell-extracellular matrix interactions. Accordingly, cytoplasmic staining in this series may reflect the production of aberrant CD44 proteins by the malignant cells [19]. Various previous data indicated some differences in biological function and timing of expression of membranous and cytoplasmic CD44. In the present study, we also observed membranous and cytoplasmic staining of CD44, however, cytoplasmic staining was focal and was noted in a few cases of grade 1 tumors. Interestingly, the grading of meningiomas depends mainly on the invasion of adjacent structures. Therefore, extensive CD44 membranous expression in high-grade meningioma may reflect a tendency toward more invasive power of neoplastic cells into surrounding structures. These findings strengthen the putative role of membranous CD44 protein in the cellular progression of meningiomas.

Based on the modified H-score, the protein expression of CD44 was categorized into weak (0–190 score) and strong (191–300 score) categories and data was correlated for significance. Accordingly, weak and strong expression of CD44 was noted in 62.9% and 37.1% of meningioma patients. When correlated with clinicopathological parameters, a significantly positive correlation was found between high-grade tumors (grade 2/3 tumors) and the presence of brain invasion status. A strong expression was observed in grade 2/3 tumors. Ninety percent of patients with grade 2/3 tumors showed strong expression of CD44. However, in grade 1 tumors it was observed in 16% of tumors (P = 0.0001). The expression of CD44 in meningioma patients with intracranial meningiomas is still controversial. Few studies demonstrated high expression in high-grade meningiomas [11, 20], and another contradictory report showed that the expression is more extensive in benign meningioma than atypical meningioma [21, 22] Concordance to our results, the significant difference in CD44 expression was reported by Mostafa et al. [11] with 81.8% positivity in grade 2 tumors and 18.2% in grade 1 tumors. These results coincide with a study done by Trenda et al. [23] and Arsene et al. [22], where a significant parallel increase in CD44 expression in high-grade meningioma tumors compared to benign meningioma. Interestingly, some studies reported a decline in CD44 expression in high-grade meningiomas Figarella-Branger et al. [21] and Arsene et al. [22]. Freitag et al. [24] reported a significantly higher expression of CD44 mRNA in low-grade tumors than in high-grade meningiomas. This discrepancy between CD44 results in the literature may be reasoned to several possibilities. Importantly, the heterogeneity of CD44 proteins in meningiomas is secondary to its post-translational modifications and differential splicing [25]. Also, the variability in the scoring methodologies among the different studies explains this discrepancy. Extensive CD44 expression in high-grade meningioma may reflect a tendency toward more invasive power of meningioma cells into surrounding structures [26]. CD44 functions in supporting tumor progression and aggressiveness can be attributed to its diverse binding ligands. In our study, strong CD44 expression correlated positively with high-grade meningioma tumors thus CD44 is a marker of aggressiveness as it is expressed in high grades and plays a major role in tumor progression.

Meningiomas are mostly benign brain tumors; however, they have a tendency to recur or even sometimes transform into more malignant tumors-typical or anaplastic with brain invasion. In this study, we observed a positive correlation between CD44 and the presence of brain invasion status. Brain invasion is defined as irregular projections of meningioma into adjacent brain tissue without an intervening layer of leptomeninges, and can be assessed only by histopathologic examination of the meningioma surgical specimen. Many lines of evidence indicate that the interaction between CD44 and hyaluronic acid-mediated tumor invasiveness and migration in various cancers [27, 28]. In a study by Pizem et al. [29], brain invasion was reported in 42.3% of meningioma patients, only when there were irregular projections of meningioma into adjacent brain tissue without an intervening layer of leptomeninges regardless of its extent. In the latest WHO CNS5 classification [30], brain-invasive benign meningioma is considered grade 2, and the study by Perry et al. [31] reported evidence that brain-invasive meningioma has a similar prognosis to atypical meningioma. In concordance with our results, a positive correlation between CD44 and brain invasion was noted by Mostafa et al. [11] and Figarella-Branger et al. [21] without statistically significant results mentioned in their studies.

The invasive activity is based on the interaction of the extracellular domain of CD44 with the extracellular matrix. CD44 can act as an intracellular signaling molecule by enhancing the expression of CD44 intracellular domain to maintain and increase the stemness of these stem-like cells. Many studies have demonstrated an important role for hyaluronan-CD44 in epithelial-mesenchymal transition (EMT). One of the important characteristics of EMT is in ability to invade and metastasize. The grading of meningioma depends mainly on the invasion of adjacent structures of the brain. Taken together extensive CD44 membranous expression in high-grade meningioma may reflect a tendency towards more invasive power of neoplastic cells of surrounding structures. These findings strengthen the putative role of membranous CD44 protein in the cellular progression of meningioma.

Next, we investigated the potential role of CD44 as a prognostic marker in meningiomas. Out of a total of 70 meningioma patients, 20% (14/70) patients developed recurrent disease and 27% (19/70) patients died within that period (Table 1). Most interestingly, out of 14 patients who developed recurrence, 6 patients (42.9%) had grade 1 tumors and out of 6 grade 1 patients, 50% (3/6) patients showed strong CD44 immunoreactivity. Strong CD44 expression showed reduced PFS and inferior OS. A study by Abd Elhakeem et al. [26] reported that CD44 expression was a poor prognostic factor for meningioma patients. In contrast, Kamamoto et al. [20] reported the lack of correlation between CD44 protein expression and OS, however found that high expression of CD44 shows a tendency towards shorter PFS (P = 0.0563). Jijiwa et al. [32] reported that expression of CD44 has been indicated to be correlated with poor survival. CD44 is significantly associated with poorer prognosis in many cancers including breast, gastric, ovarian, and oral cancers. In a study by Boxberg et al. [33], they reported CD44 as an independent prognostic factor for poor OS and PFS in patients with advanced oral cancer. In a study by Lin et al. [34] they revealed that CD44 expression was significantly associated with high TNM stage and poor OS in ovarian cancer. Zanjani et al. [35] also reported that high CD44 overexpression is statistically associated with more aggressive tumor behavior, tumor grade, and poor survival in clear renal cell carcinoma. We also evaluated the impact of CD44 in relation to treatment offered to meningioma patients. We found that if CD44 expression was to be found weak and patients were treated with surgery only then the incidence of death was significantly low as compared to patients treated with surgery followed by adjuvant therapy. A similar difference we observed for PFS, however, the data failed to reach statistical significance. Thus, CD44 might be helpful to prevent patients from unnecessary overtreatment and thereby prevent them from drug-induced toxicity. Using ROC curves, our results of CD44 as significant potential parameter for meningioma patients were confirmed. We found that CD44 could be a potential marker and it has efficacy in discriminating high and low-risk patients that might have reduced recurrence and shorter OS. However, the limitation of the present study was the small size of the patient cohort of grade 2/3 tumors compared to grade 1 tumors. Grade 2/3 tumors of meningioma are more aggressive in nature than grade 1 tumors. Therefore, further studies with a larger sample size of grade 2/3 tumors are warranted to validate our current study data.