Abstract

INTRODUCTION

The primary brain tumors account for less than 2% of all human cancers, but cause a disproportionate burden of cancer-related morbidity and mortality. They are the most common solid tumors of childhood and after leukemia are the leading cause of death in children. They account for 20% of all pediatric malignancies. Unfortunately, the incidence of brain tumor is on the rise and about 15000 new cases of pediatric brain tumors are diagnosed each year in USA. The overall annual incidence in USA of pediatric malignant brain tumor is about 28 per million children <14 years.[1] But data regarding the incidence of pediatric brain tumors in India and especially in our setting are lacking. The most prevalent primary brain tumors among the pediatric population are astrocytomas, ependymomas, medulloblastomas, craniopharyngiomas, choroid plexus neoplasms, etc. Seventy percent of these pediatric brain tumors arise in the posterior fossa. In the infratentorial region, the common tumors are medulloblastoma, pilocytic astrocytoma, brain stem glioma, and ependymoma. Among astrocytomas, pilocytic astrocytoma is the most common glioma in children, and represents 10% of cerebral and 85% of cerebellar astrocytomas.[2] There is enormous heterogeneity in the pathogenesis of brain tumors. Many studies have been undertaken so far to analyze the role of Ki67 and p53 in adult astrocytomas and also assess their significance as prognostic factors in adult glioma. Both p53 and Ki67 have been implicated in gliomagenesis in the case of adults. However, pediatric gliomagenesis seem to follow different molecular pathways than the adults. Not only studies regarding pediatric brain tumors are rare, different studies have given varied propositions regarding the role of p53 and Ki67 in pediatric brain tumors. This work was done to analyze the histopathological spectrum of pediatric brain tumors in our setting and to study the possible role of p53 and Ki67 in their prognosis.

MATERIALS AND METHODS

Sixty-one pediatric brain tumor specimens of patients aged 0 to 15 years were included in this study over a period of 2 years. The case selection was random with no bias. Clinical details, namely age and site were recorded in each case. The haematoxylin and eosin (H and E) stained slides of all 61 cases were studied and grading was done according to WHO criteria. One or two representative blocks of formalin-fixed paraffin-embedded tissue in 52 cases out of 61 were selected and serial 5 μm thick sections were cut and taken on poly-L-lysine coated slides for immunohistochemical stains with p53 and Ki67 using standard immunohistochemical procedure. Antibody used was ready to use pre diluted antibody from Bio-Genex (USA). Result of Ki67 immunostaining was interpreted as labeling index (Ki67 LI) – as percentage of positively stained nuclei. P53 scoring was calculated by studying a minimum of five fields in the highest labeled areas and the scoring was assessed as follows: 0 = no positive nuclei, 1 = < 5% positive, 2 = 5–30% positive, 3 = >30% positive.[3] Survival was defined as the interval between biopsy proven diagnosis and death or date of last follow up, up to 6 months. The software used for this purpose was software version 6.0. Tulsa Oklahoma: Statsoft, Inc; 2001 and SPSS 17.1 August 2007.

RESULTS

Of 61 observed cases, most common were medulloblastomas (22.9%) and pilocytic astrocytomas (22.9%). The histopathological spectrum, mean age, sex distribution of these 61 cases of pediatric brain tumors are shown in Table 1.

Table 1

DISCUSSION

Pediatric brain tumors are rare and the management of each child has to be individualized depending upon the clinical presentation, age, histology, tumor location, size, etc. All patients with malignant brain tumors require postoperative radiotherapy. The quality of life of those children who had been treated for brain tumor is typically poor. Very few long-term survivors are expected to live a normal life. However, there is rarity of information regarding the genetic abnormalities underlying the brain tumors in children. Identification of these genetic lesions is the key to develop targeted therapeutics (smart drugs) that can eradicate brain tumors without affecting other organ systems in growing children, thus ensuring a better quality of life.

In our study, the two commonest pediatric tumors were pilocytic astrocytomas and medulloblastomas. This is in keeping with published literatures; however, Kumar et al., had reported a higher incidence of medulloblastomas amongst Indian children.[4] We reported a higher percentage of craniopharyngioma (10.5%) than both Yates et al. and Chan et al.[5] However, Tobias et al. and Kumar had reported similar incidence of craniopharyngiomas as ours.[4,6] In contrast to most studies we had higher percentage of glioblastomas in children, the reason for this is unknown. Also, we did not encounter any germ-cell tumor that is reported quite frequently in many Asian studies specially from far East.

Just over half of our tumors were located supratentorially. PA and medulloblastomas were most common in posterior fossa. Patients with astrocytomas presented at a higher age in this series than that reported in other studies, probably because of greater number of glioblastoma cases. Childhood primitive neuroectodermal tumor (PNETs) presented at a mean age of 7, similar to the observations made by Grotzer et al. and Chan et al.[5,7] There was equal distribution of boys and girls suffering from brain tumor when all tumors were taken together; however, girls outnumbered boys in case of PAs, while male predominance was found in medulloblastomas.

Different series have reported varying ranges of Ki67 LI and p53 immunostaining in pediatric brain tumors. The results of these are sometimes overlapping and even conflicting with no common consensus.

For analyzing the Ki67 LI we chose the “hot spots” or maximal labeling index areas.[8] as randomly chosen areas underestimates the growth fraction by combining active and quiescent areas. The mean Ki-67 in case of PA and diffuse infiltrating astrocytoma (DIA) were typically low similar to data published in the world literature,[9] The LI for DIA and PA were significantly lower than that of high-grade malignant gliomas. This is in keeping with the observation by Ho et al.[8] Though Ki67 correlated significantly with other grades, it was not of much importance in differentiating between pilocytic astrocytomas with diffuse infiltrating variety corroborating the finding of Giannini et al.[10] Matsumoto et al., who worked in Japan also reached to the same conclusion.[11] However, Ki-67 LI among different studies vary considerably in range possibly because of storage, processing, fixation, and different staining protocols.

This study has documented a higher Ki67 LI in case of medulloblastomas than that by Sarkar et al.[12] We also found that there was a significant inverse association of Ki67 LI with survival in case of medulloblastomas similar to the observations made by Grotzer et al.[7] and Shim et al.[13] But other studies by Mirabell et al., had reported different results regarding this association.[14]

The reported frequencies of p53 alterations in pediatric astrocytic tumors vary considerably. Although initial studies indicated that childhood malignant gliomas rarely exhibit p53 mutation,[15,16] more recent studies by Sung et al. and Sure et al., have suggested a role of p53 in pediatric gliomagenesis.[17,18] Unlike other series, we found p53 expression in fair number of cases in PA implying its possible role in gliomagenesis. We observed p53 expression in 35.7% cases of PA in keeping with the observation of Hayes et al.[19] A high percentage of high-grade gliomas strongly expressed p53 in this study, similar to that of Suri et al., who also observed high incidence of p53 alteration in pediatric glioblastoma.[20] Bhattacharjee et al., also found that the overall frequency of p53 immunoreactivity was 47% in pediatric high-grade astrocytomas that was similar to the one reported for adult astrocytomas.[3] However, contrary to our findings, Rasheed et al., showed p53 immunoreactivity in only 16% of pediatric high-grade glioma patients, and concluded that p53 has limited role in pediatric gliomagenesis.[21] Also, p53 score was significantly lower in PA and grade-II astrocytomas than the high-grade ones (anaplastic astrocytoma, glioblastoma multiforme) similar to results obtained by Matsumoto et al.[11] p53 alteration, also correlated inversely with survival amongst medulloblastoma cases in our study. Similar observations were made by Woodburn et al. and Jaros et al.[22,23] Both p53 and Ki67 taken together and individually had significant association with survival in these cases, in the present study. The relation of p53 and Ki67 with medulloblastomas so far reported conflicting results in many series. Ertan et al., showed that the MIB-1 value and p53 immunoreactivity had no relation with prognosis in pediatric medulloblastomas contrary to our findings.[24] Ki67 in this study had better predictive value than p53.

In this study, p53 and Ki67 were not only found to be significantly associated with survival individually, but taken together they also were significantly related to survival in astrocytoma patients in keeping with Tihan et al.[25] However, Ki67 was a better marker than p53 in astrocytoma series.

CONCLUSION

In this study, we feel that both Ki67 and p53 have potential diagnostic and prognostic use in the diagnosis of medulloblastomas, astrocytomas, and differentiating between various grades of astrocytoma. This may be particularly useful in small/stereotactic biopsies where deciding on the grade is a diagnostic problem. We found Ki67 to be a better diagnostic marker than p53 in both medulloblastomas and astrocytomas.

Footnotes

REFERENCES