Among neurosurgical tumors, meningiomas are usually considered to be a clinically benign entity. However, the presence of atypical/malignant histopathological features and, sometimes, the localization of the tumor potentiates their risk of recurrence (Louis et al., 2000). Although the WHO classification includes well-defined histological criteria, there are some unusual cases in which establishing a diagnosis of high-grade meningioma is extremely difficult (Bruna et al., 2007). Accordingly, the search for prognostic factors that could be used at diagnosis to identify a subgroup of tumors that are at a high risk of relapse represents a major challenge. Among all disease characteristics, those parameters that are related to the biology of the neoplastic cells such as the presence of genetic abnormalities at the DNA level, as well as the proliferative ability of human tumors, have frequently been shown to contain predictive information for disease outcome. In this sense, previous reports have indicated that the presence of DNA aneuploidy detected in tumors from the central nervous system is frequently associated with malignancy (Tsukazaki et al., 2000; Gardina et al., 2008; Alexiou et al., 2009). Similarly, in neurological tumors, a high proliferative rate has been associated with a worse clinical outcome (Johannessen and Torp, 2006; Yoshida et al., 2010; Habberstad et al., 2011). Despite this, for meningioma tumors, few reports have been published in which the prognostic value of both parameters has been explored.
In the current study, the mean Ki-67 LI was correlated significantly with the histological grade of meningioma. Grade III tumors tended to have a statistically significant higher Ki-67 LI compared with grades II and I tumors. These findings were in agreement with previous studies that have confirmed an increase in the Ki-67 proliferation index within the spectrum of meningiomas and its prognostic significance (Takahashi et al., 2004; Moradi et al., 2008; Shayanfar et al., 2010).
However, in all grades, the observed mean Ki-67 LIs were different from those reported in other studies. This considerable variation from one study to another could be related to several aspects of the immunohistochemical procedure, for instance, the choice of tumor areas to count and the numbers of cells counted to calculate a LI. Tumor heterogeneity with regional differences in cell proliferation is well known; thus, tumor sampling becomes an important source of error as it is crucial to select the block with representative tumor tissue for calculation. As a rule, the area with the most malignant histological appearance is selected for the estimation of proliferative activity. The definition of positive immunostaining is another element of uncertainty, and only distinct nuclear staining should be interpreted as positive. These aspects are the basis of the interobserver variability associated with the determination of proliferative indices (Prayson, 2005).
Between grade I and II/III meningiomas, all studies found a statistically significant difference in the Ki-67/MIB-1 LIs, whereas this was not always the case between grade II and III tumors. For this reason, some authors group the two latter under the entity ‘aggressive meningiomas’. Because of overlap of indices between the malignancy groups, it is difficult to pinpoint a specific LI indicative for a specific tumor grade. Accordingly, a low index does not always indicate a low-grade meningioma as grade II, III tumors may show low proliferative activity as well. In contrast, a high proliferative index in an otherwise benign-looking meningioma should call attention to a more aggressive tumor. Nevertheless, the Ki-67/MIB-1 LI of a particular tumor should be interpreted with caution and in conjunction with established histopathological features of malignancy (Abry et al., 2010).
In the present study, we found no correlation between Ki-67 expression and other demographic and clinical parameters such as age, sex, and tumor location. Baumgartner and Sorenson (1996) have reported a high Ki-67 LI in pediatric meningiomas, with a higher frequency of recurrence. However, Sandberg et al. (2001) have shown that Ki-67 LI in these tumors did not differ significantly from that in adults and added that the more aggressive features of meningiomas in children may be attributable to factors other than the growth rate. Some reports have found a statistically significant higher Ki-67 LI in male patients than in female patients (Matsuno et al., 1996; Wolfsberger et al., 2004), whereas others have not (Roser et al., 2004; Korhonen et al., 2006). In terms of tumor location, most meningiomas arise in intracranial, intraspinal, and orbital locations, and obvious regional differences in proliferative activity have not been found; however, in one study, lower indices in spinal meningiomas were found (Roser et al., 2006).
The assessment of abnormal cellular DNA content can provide clues about the aggressiveness of various tumors and has been shown to be of considerable value in identifying different prognostic patient subsets (Alexiou et al., 2008). In the current study, 44% of the meningioma patients studied showed DNA aneuploidy, with nine (18%) cases showing hypodiploidy and 13 (26%) cases showing hyperdiploidy. This frequency is consistent with that reported by Ironside et al. (1987) (41%). However, different values of DNA aneuploidy have been reported by Arai et al. (1998) (67%) and Maíllo et al. (1999) (14%). The discrepancy in the incidence of aneuploid tumors could be attributed to technical pitfalls because of the use of paraffin-embedded samples or fresh material, lack of approaches used for the exclusion of cell multiplets, analysis of a short series of patients, and/or to the criteria used for the definition of DNA aneuploid populations. In this sense, consensus reports (Shankey et al., 1993; Ormerod et al., 1998) have pointed out that the best results are usually obtained by using either fresh or frozen material. Further studies, on the basis of larger series of meningioma patients in whom a comparative analysis of the results is obtained in fresh and archival material, are required to clarify this question.
Our results showed that DNA ploidy correlated with the tumor histological grading, as there was an increase in the percentage of aneuploid tumors with an increase in tumor grading. This was in full agreement with Spaar et al. (1987) and Butti et al. (1989), who reported a significantly higher rate of aneuploid cell lines in malignant meningiomas using flow cytometry. Also, Cruz-Sanchez et al. (1993) observed that DNA aneuploidy was significantly associated with tumor recurrence. In contrast, Akachi et al. (1991) found no increased DNA aneuploidy in malignant meningiomas, and Nishizaki et al. (1993) showed that evaluation of tumor prognosis on the basis of the presence of aneuploid cell lines yields uncertain estimates. No correlation was found in the present study between DNA ploidy status and the clinical characteristics of the patients. However, Maíllo et al. (1999) reported an association of DNA aneuploidy with older age and tumor location at the cerebral convexity in their studied meningioma cases.
Only a few previous studies have attempted to define hypodiploid and hyperdiploid cell lines in meningiomas. Although Ironside et al. (1987) found six hypodiploid and 10 hyperdiploid cell lines among 16 DNA aneuploid tumors, Cruz-Sanchez et al. (1993) detected 10 hypodiploid and seven hyperdiploid cell lines among 17 aneuploid tumors and found a slightly increased tendency of recurrence in the hyperdiploid tumor group. There is only sparse published evidence on the possible relevance of either hypodiploidy or hyperdiploidy for different biological and therapeutic behaviors of intracranial tumors. Sandberg and Turc-Carel (1987) associated chromosomal hypodiploidy with an aggressive behavior in meningiomas. For glioma cell lines, Shapiro (1989) reported that hypodiploid or near-diploid cell lines become more readily resistant to chemotherapy, whereas hyperdiploid cell lines are more sensitive.
In this study, we also confirmed previous findings of the existence of an association between aggressive meningioma subtypes and a higher proliferative rate of tumor cells as evaluated by the SPF (May et al., 1989; Cruz-Sanchez et al., 1993). SPF was also found to be significantly higher in aneuploid than in diploid tumors, which agrees with that reported by Zellner et al. (1998). Furthermore, from the prognostic point of view, Maíllo et al. (1999) reported that the proportion of S-phase cells is an independent prognostic factor for relapse prediction in meningiomas.
In terms of the relationship between the DNA ploidy status and Ki-67 expression, there was a statistically significant difference in Ki-67 LI between aneuploid and diploid tumors. Aneuploid tumors had a significantly higher mean Ki-67 LI compared with diploid tumors. This was in agreement with Meixensberger et al. (1996), who identified a similar significant correlation between ploidy status and Ki-67 LI in their prospective study of human meningiomas. They added that the nuclear DNA content is an important factor in predicting the risk of recurrence and poor clinical outcome after meningioma surgery.
The results of this study suggest that Ki-67 LI and DNA ploidy can act as potential supplements in determining the histological grade of meningiomas. Furthermore, they might be beneficial as additional tools in histological borderline cases where one cannot readily differentiate an atypical meningioma from a benign or a malignant one. However, further studies are recommended to correlate Ki-67 expression and DNA ploidy with tumor recurrence, progression, and treatment.
There are no conflicts of interest.
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