Prognostic factors of pediatric pineal region tumors at a single institution

This study aimed to identify factors of a worse prognosis among different histological types of pineal region tumors in pediatric patients treat at a single institution in a 30-year period. Pediatric patients (151; < 18 years of age) treated between 1991 and 2020 were analyzed. Kaplan-Meyer survival curves were created, and the log-rank test was used to compare the main prognostic factors in the different histological types. Germinoma was found in 33.1%, with an overall 60-month survival rate of 88%; the female sex was the only factor of a worse prognosis. Non-germinomatous germ cell tumors were found in 27.1%, with an overall 60-month survival rate of 67.2%; metastasis upon diagnosis, residual tumor, and the absence of radiotherapy were associated with a worse diagnosis. Pineoblastoma was found in 22.5%, with an overall 60-month survival rate of 40.7%; the male sex was the only factor of a worse prognosis; a tendency toward a worse outcome was found in patients < 3 years of age and those with metastasis upon diagnosis. Glioma was identified in 12.5%, with an overall 60-month survival rate of 72.6%; high-grade gliomas were associated with a worse prognosis. Atypical teratoid rhabdoid tumors was found in 3.3%, and all patients died within a 19-month period. Pineal region tumors are characterized by the heterogeneity of histological types, which exert an influence on the outcome. Knowledge of the prognostic factors for each histological types is of extreme importance to the determination of guided multidisciplinary treatment.


Introduction
The pineal gland -also denominated the epiphysis -is a brain structure located in the posterior incisural space bordered above by the splenium of the corpus callosum and pillars of the fornix, below by the anterosuperior portion of the cerebellum, anteriorly by the mesencephalic roof and lamina quadrigemina, laterally by the pulvinar of the thalamus and para-hippocampal gyrus bilaterally, and posteriorly by the apex of the free margin of the tentorium [1].
Pineal region tumors are rare, corresponding to 0.4 to 1% of intracranial tumors in the adult population, and are more frequent in the pediatric population, with an incidence ranging from 2.7 to 11% [2][3][4]. These tumors are characterized by the heterogeneity of histological types, with germ cell tumors and pineal parenchymal tumors accounting for the largest portion (> 70%), followed by tumors derived from adjacent structures, such as glioma, meningioma, ependymoma, embryonal tumors (atypical rhabdoid/teratoid tumor), and metastasis. The management and treatment of these tumors include the study of tumor markers in the blood and cerebrospinal fluid (beta-HCG and alpha-fetoprotein), biopsy of the tumor, treatment of hydrocephaly by endoscopy or shunt, chemotherapy, radiotherapy, and surgical resection. The outcome depends primarily on the histological type of the tumor.
The aim of the present study was to investigate the prognostic factors of each histological type of tumor in the pineal gland region in the pediatric population and long-term outcome of patients treated at a single institution in a 30-year period.

Study design and inclusion of patients
A retrospective study was conducted involving the analysis of electronic medical and physical records of patients treated at the Neurosurgery Service of the Escola Paulista de Medicina and Instituto de Oncologia Pediátrica de São Paulo (IOP/GRA ACC ) between 1991 and 2020. This project received approval from the ethics committee of IOP and Universidade Federal de São Paulo (certificate no. 4.332.210).
Pediatric patients (< 18 years of age) with a diagnosis of a tumor in pineal gland region determined by magnetic resonance were included. Patients with non-neoplastic lesions, such as a pineal cyst, were excluded.

Degree of resection and outcome
The degree of resection was classified as total, subtotal (residual tumor ≤ 1.5 cm 3 ), and open biopsy (residual tumor > 1.5 cm 3 ). Overall survival was defined as the time in months from the date of the diagnosis (considered the date of the 1st imaging exam) to death. Progression-free survival was defined as the time in months between the date of diagnosis and the date of the recurrence or progression of the tumor in 60 months. Recurrence was considered the return of the disease after surgery, chemotherapy, or radiotherapy that had eliminated the disease based on magnetic resonance of the head and/or tumor markers.

Statistical analysis
Statistical analysis was performed using Kaplan-Meyer survival curves and the Mantel-Cox log-rank test when two groups were compared or the log-rank test for trend when more than two groups were compared. Qualitative variables were analyzed using either the chi-squared test or Fisher's exact test, depending on the sample size and distribution (normal or non-normal) for each set of samples. The Kruskal-Wallis test was used for multiple comparisons of medians of nonparametric samples. A p-value ≤ 0.05 was considered indicative of statistical significance. Data analysis and the creations of graphs were performed using GraphPad Prism 8, version 8.0.1.

Germ cell tumors
Pure germinomas were the most prevalent among the tumors of the pineal gland region, accounting for 33.1% (50/151). The male population predominated in this group, accounting for 96% of cases (47/50).
Median age upon diagnosis was 13 years (range: 6 to 25 years). Median time between the onset of symptoms and the diagnosis was 2 months (range: 0 to 47 months), which was the longest time among the different histological types. The median of the largest diameter of the tumor upon diagnosis was 3 cm (range: 1.4 to 5 cm).
In this group, 19 patients were submitted to surgery (38%), 13 of whom (68.4%) were submitted to total resection, three were submitted to subtotal resection, and three were submitted only to biopsy of the tumor, from whom fragments of the suprasellar tumor were obtained. Bifocal pure germinoma was found in 13 patients (26%) and was not related with the prognosis (OS in 5 years was 92.3% in bifocal germinoma vs 86.5% in non-bifocal germinoma with p = 0.78).
The only factor related to a worse prognosis on the group of germinomas was the female sex. Positivity for the beta-HCG marker in the cerebrospinal fluid which was found in 20% of pure germinomas was not associated with a worse prognosis (Fig. 1).
Non-germinomatous germ cell tumors (NGGCT) accounted for 27% of all tumors of the pineal gland region (41/151). Median age at diagnosis was 9 years (range: 0 to 16 years), and median time between the onset of symptoms and the diagnosis was less than 1 month (range: 0 to 66 meses). Median size of the largest diameter of the tumor upon diagnosis was 3.8 cm (range: 0.9 to 11.8 cm). Bifocal NGGCT was found in 7 patients (17%) and was also not related with the prognosis (OS in 5 years was 57.1% in bifocal NGGCT vs 69.2% in non-bifocal NGGCT with p = 0.48). The mortality rate was 29.2% (12/41). From all death, tree were malignant NGGCT (embrionary carcinoma and yolk sac tumor), eight were mixed tumor, and one was immature teratoma.
The factors associated with a worse diagnosis in the group of non-germinomatous germ cell tumors were metastasis at diagnosis (p = 0.009); residual tumor after the conclusion of treatment, including primary surgery or second-look surgery, chemotherapy, and radiotherapy (p = 0.0015); and the non-performance of radiotherapy (p = 0.04). Alpha-fetoprotein level (> or < 1000 ng/ml) was not associated with the prognosis (p = 0.41) (Fig. 2).

Pineoblastoma
Pineoblastoma constituted the third most prevalent group in our series, accounting for 22.5% (34/151) of tumors of the pineal gland region. Median age at diagnosis was 5.5 years (range: 0 to 17 years). Median time from the onset of symptoms to diagnosis was less than 1 month (range: 0 to 10 months). Median size of the largest diameter of  the tumor at diagnosis was 4.3 cm (range: 2.8 to 7 cm). This group has the highest rate of dependence on ventricleperitoneal shunt (88.2%; 30/34) (p = 0.0002). Twenty-nine patients were submitted to surgical resection, and total resection was possible in 17 (58.6%). The general mortality rate was 52.9% (18/34), and 5-year survival was 38.9%. This was the group with the second highest mortality rate, following the few cases of embryonal tumor (atypical rhabdoid/teratoid tumor).
The male sex was the only statistically significant factor associated with a worse prognosis (p = 0.03). Age less than 3 years and metastasis had a tendency toward a worse prognosis (p = 0.09 and 0.07, respectively). Radiotherapy, tumor size, and degree of resection were not associated with the prognosis in our series (Fig. 3).

Glioma
Glioma of the pineal parenchyma accounted for 12.5% (19/151) of pineal region tumors, with a mortality rate of 26.3% (5/19). Median age at diagnosis was 11 years (range: 0 to 22 years), and median time between the onset of symptoms and diagnosis was less than 1 month (range: 0 to 6 meses). The median size of the largest diameter of the tumor at diagnosis was 3.2 cm (range: 0.9 to 6.1 cm).
Fifteen patients in this group were classified with lowgrade glioma (Grades I and II, according to the World Health Organization [WHO]), and four were classified with high-grade glioma (Grades III and IV, according to the WHO), all of whom died. Mean survival was 16.5 months (5 to 31 meses). Six patients underwent endoscopic biopsy, and one underwent stereotactic biopsy, all of which (100%) contributed to the histopathological diagnosis.
A total of 68.4% (13/19) were submitted to surgical resection, only four of whom received total resection (30.7%). Compared to the other histological types, this group was the poorest with regard to the degree of resection.
High-grade gliomas (III and IV) had a worse prognosis compared to low-grade gliomas (I and II). The degree of resection and need for a ventriculoperitoneal shunt were not associated with the prognosis in our series (Fig. 4).

Embryonal tumor-atypical teratoid rhabdoid tumor
Five patients had a histopathological diagnosis of atypical teratoid rhabdoid tumor in the region of the pineal gland, all of whom were diagnosed at 1 year of age or younger. All were submitted to surgery (three total resections and two subtotal resections). Median size of the largest diameter of the tumor was 5.5 cm (range: 4.4 to 6.1 cm). Median survival was 11 months, and all patients died within 24 months, excepted 1 that lost follow-up ( Table 2). Two of the deaths were due to clinical complications: one from pneumonia and the other from neutropenic enterocolitis.

Discussion
Pineal region tumors are rare, accounting for 0.4 to 1% of intracranial tumors in the adult population at large European and American centers [5,6], and are more frequent in the pediatric population, with an incidence ranging from 2.7 to11% [3]. A higher incidence was reported in a Japanese series (3.2 to 4%) [7]. According to Herrada-Pineda, the incidence is between 3 and 8% [8]. Raimondi and Tomita reported an incidence of 9%, which is one of the highest in the literature [9]. Oi   Japanese populations [13]. In agreement with this statement, we found a prevalence of 7.3% for tumors of the pineal region, which is higher than the figure found in most Western series. Analyzing the incidence of these tumors in terms of sex, Ali-Hussain et al. found a male to female ratio of 3:1 [2,14], which is the same ratio found in the present series. Considering the distribution per sex within histological groups, the difference was greater for germ cell tumor. Germinomas were more prevalent in the male sex compared to the female sex, and this difference was accentuated when considering the pineal region, with the ratio ranging from 5:1 to 22:1 and a median of 14:1 [15], which is close to the ratio found in the present series (15:1). The most widely accepted theory for the difference between sexes was proposed by Sano and regards that the fact that closure of the neuropore occurs later in females than males; thus, the migration of embryonal cells reaches deeper portions of the nervous system in the formation of membranes, reaching the neuro-hypophysis more commonly, whereas this migration reaches more superficial portions of the neural tube in males, such as the pineal region. This theory explains the greater prevalence of germ cell tumors in the pineal region in males and the greater prevalence of germ cell tumors in the sellar region over the pineal region in females [16]. Genetic and hormonal factors may also play a role. Jennings et al. found an association between germ cell tumors and an increase in the secretion of gonadotrophins in patients with cryptorchidism, testicular feminization, and gonadal dysgenesis [6].
The heterogeneity of histological types is justified by the variety of cell types found in the region, such as germ cells, parenchymal cells of the pineal gland, glia, and neuroepithelial cells. According to the American research group Surveillance Epidemiology and End Results (SEER), germ cell tumors and pineal parenchymal tumors account for 89% of tumors in this region [2]. Mottolese reports the following distribution: 27% germ cell tumors, 27% pineal parenchymal tumors, and 17% glioma [3]. According to Wong, the difference is accentuated, with germ cell tumors corresponding to 50-80%, pineal parenchymal tumors 3.6-21.8%, and glioma 2.4-8.1% [17]. However, these data refer to the general population. In the present sample of only pediatric patients, we had the following distribution: 60.2% germ cell tumors, 22.5% pineal parenchymal tumors, and 12.5 glioma. Germ cell tumors can also be subdivided into two large groups: germinomas, accounting for 50 and 75%, and non-germinomas, which are represented by choriocarcinomas, embryonal carcinomas, endodermal sinus tumors, and mixed tumors (with components of more than one histological type) as well as pure, mature, or immature teratomas. This proportionality of histological types was maintained in the present sample, with germ cell tumors and pineal parenchymal tumors accounting for more than 80% of the total. Considering only germ cell tumors, germinomas corresponded to 55%.

Germ cell tumors
Currently, the gold standard for the treatment of nonmetastatic pure germinomas is chemotherapy followed by radiotherapy of the entire ventricular system and a boost at the tumor site. The boost can be omitted in cases of a complete response to chemotherapy. Metastatic tumors require radiotherapy of the entire neuroaxis as well as a boost in the primary tumor and metastatic tumors, without additional chemotherapy, although there is evidence of radiotherapeutic treatment without boost when chemotherapy is performed prior to radiotherapy [18]. Bifocal tumors in the region of the pineal gland and sellar region are not considered metastatic tumors and should therefore be treated with the same protocol as localized germinomas [18]. According to Mallucci and Van Battum, in the presence of bifocal tumors with negative tumor markers and brain MRI characteristics (but not pathognomonic) of germinoma, such as hypo-or iso-intensity at T1 and iso-intensity at T2 with homogeneous capture by contrast without the continuity of both tumors, it is possible to exclude non-germinomatous germ cell tumors, making germinoma the only possible diagnosis [5,19]. In the present series, seven patients with non-germinomatous germ cell tumors met the criteria for bifocal tumors, but all were positive for some tumor marker, lending strength to the theory of both authors. However, Cuccia reported a case of pineoblastoma with a bifocal tumor and negative markers with an image similar to germinomas, thereby considering biopsy indispensable in the case of bifocal tumors with negative markers [20]. Neither pure germinomas nor NGGCT with bifocal lesions were related with poor outcomes in our series.
Tumor markers are essential during the follow-up of these tumors to evaluate the response to clinical treatment and should be used together with imaging exams. Cases of the recurrence of the tumor and negative (previously positive) markers could be what is known as "growing teratoma syndrome," which is a rare condition first described in patients with extracranial germ cell tumors that consists of an increase in the tumor following the complete normalization of previously high tumor markers and whose component is exclusively a mature teratoma [21,22]. It is postulated that chemotherapy induces immature germ cells to differentiate into the mature teratoma phenotype [23]. Some studies also suggest the participation of radiotherapy or even irradiation secondary to multiple sessions of computed tomography as the trigger for this differentiation and growth of the component of the mature teratoma [22,24,25]. Other suggest that treatment of the malignant components of germ cell tumors "enables" the uninhibited growth of the mature teratoma component [25]. Treatment consists of radical surgery, for which the prognosis is good [26]. We had two cases of "growing teratoma syndrome", both of which were submitted to total resection and had a good outcome.
B-HCG level as a prognostic factor in pure germinomas is an issue of debate in the literature. Recent studies have found no evidence of this association [27], whereas previous studies reported a better prognosis for non-B-HCG-secreting germinomas [28]. In the present sample, we found no evidence of an association between B-HCG-secreting germinomas and a worse outcome.
The risk factors associated with a worse prognosis in cases of non-germinomatous germ cell tumors are high alpha-protein levels (> 1000 ng/ml) and residual tumor after all lines of treatment instituted (primary or secondlook surgery, chemotherapy, and radiotherapy) [29]. The first factor was not associated with mortality in our series, but the second factor was associated, which lends strength to the current recommendation to be aggressive with residual non-germinomatous germ cell tumors. We also found that the presence of metastasis and the absence of radiotherapy were factors associated with a worse prognosis.
The overall 60-month survival rate for germinomas at our service was close to 90%, which is an excellent rate and similar to that found at other large centers specialized in childhood tumors [13,30].

Pineoblastoma
Pineoblastomas are rare malignance embryonal tumors, the prevalence of which is higher in children and adolescents, accounting for < 1% of all pediatric tumors in childhood [31]. These tumors have an aggressive behavior, with a high frequency of metastasis to the neuroaxis (around 15% identified at diagnosis) and a high mortality rate [32].
Lin et al. investigated prognostic factors associated with pineoblastoma in the pediatric population using the SEER databank with 132 patients. Age > 5 years, radiotherapy, and radical resection were associated with a higher survival rate, whereas tumors with a diameter > 30 mm were associated with a worse outcome [33].
Parikh et al., Biswas et al.,and Tate et al. [31,34,35] also found an association between age and prognosis, reporting a worse outcome among children less than 5 years of age. The faster progression time in these children and higher response rates to chemotherapy in older children are some of the justifications for the worse outcome in younger children. These researchers also associated the occurrence of metastasis with lower survival rates, similarly to those seen in medulloblastomas. We also identified a tendency toward a worse prognosis in patients with metastasis at diagnosis (p = 0.07). This association was not found in the SEER databank [33].
In the most recent consensus on pineal parenchymal tumors, in which a genomic study was conducted, five molecular subtypes were identified with distinct clinicalepidemiological characteristics [36]. The MYC/FOXR2 and RB1 subgroups are more prevalent in the population less than 3 years of age (73 and 76%, respectively) and have a much worse outcome compared to other subtypes, with overall five-year survival rates of 20.6 and 26.8%, respectively [36]. One of the justifications raised for these low survival rates is the non-use of craniospinal irradiation radiotherapy in very young children due to the number harmful effects on neuropsychomotor development [36]. In the present study, we also found a worse outcome in this population, with an overall survival rate of 25 to 45% among patients less than three years of age.
Cuccia analyzed 12 patients with pineoblastoma (median age: 7 years) and found an overall 1-year and 5-year survival rate of 66.6% and 50%, respectively [37]. These figures were respectively 88% and 58% in the study by SchilD [38] and 85% and 60.5% in the study by Lin [33]. In the present sample, the median age of which was 5 years, we found an overall 1-year and 5-year survival rates of 84, 5%, and 40.7%, respectively. This poorer outcome may be attributed to the younger median age in the present sample compared to that of the other studies, underscoring the considerable impact of age upon presentation for this type of tumor.

Glioma
The present results show a slight predominance of the male sex (57.8%) and a median age of 11 years. The literature also describes a predominance of the male sex and age of presentation between 5 and 20 years [39]. Regarding the size of the tumor at diagnosis, the median of the largest diameter was 3.2 cm in the present study, which is also comparable to the size reported in previous series, likely due to the small space in which the tumor is confined and the proximity to structures that hinder tumor expansion or infiltration. Thus, small tumors are sufficient to produce symptoms [40].
Regarding surgical aspects, the low rate of total resection (30%) may be explained by the intrinsic and infiltrative characteristics of this type of tumor. Endoscopic biopsy had 100% sensitivity in detecting this histological type with no adverse effects, making it highly recommendable in the management of these tumors. The most widely used access was the infratentorial supracerebellar approach in the sitting position due to the greater experience of the surgeon and the fact that it enables ample access to the pineal region, permitting the dissection of the venous complex, which is ideal for small tumors centered on the midline without extension above the tentorium. The use of a ventriculoperitoneal shunt was not associated with the prognosis in the present series and was also not more effective than endoscopic third ventriculostomy.
The present data are in agreement with data reported in the literature demonstrating a poorer outcome with highgrade compared to low-grade gliomas [41]. All patients with high-grade tumors died within 31 months. However, the 12-month survival was very satisfactory in this series (89.4%) compared to the overall rate described in the literature for the general population (60%) [20]. Five-year disease-free survival was > 70%. This result is justified by the higher rate of patients with low-grade tumors in the present investigation compared to that reported in previous studies, with rates of high-grade tumors surpassing 65% [40,42].

Embryonal tumors -AT/RT
Atypical teratoid rhabdoid tumors (Grade IV according to the WHO) are rare, malignant, and more commonly affect children less than 3 years of age, with a very poor prognosis. The main histopathological characteristic that enables its differentiation is the absence of the INI1 marker in the immunohistochemical analysis. The main location within the central nervous system is supratentorial. Such tumors in the pineal region are rare, with few cases described in the literature, most of which are case reports or small series [43]. The present sample included five cases of embryonal tumors -AT/RT, with a median age 3 months (range: 1 to 12 months).
Patients benefit from radical surgery, when possible, as well as early, aggressive chemotherapeutic and radiotherapeutic treatment, but overall survival is low, ranging from one to 46 months [44]. In the present series, all five patients were submitted to radical surgical resection, 60% of whom (3/5) were achieved total resection. All were submitted to aggressive chemotherapy and overall survival ranged from 2 to 19 months.

Conclusion
Pineal region tumors are diverse in terms of histological type. The present study sought to identify the main risk factors associated with each type. The female sex was the only factor related to a worse diagnosis among germinomas. Residual tumor, the absence of radiotherapy, and metastasis were independently associated with a worse prognosis in cases of non-germinomatous germ cell tumors. The male sex was the only significant factor associated with a worse prognosis in cases of pineoblastoma, although age less than 3 years and metastasis at diagnosis demonstrated a tendency toward a worse outcome. High-grade glioma was associated with a worse outcome and was the histological type with the lowest rate of total resection; the use of a shunt was not associated with the prognosis in such cases. Atypical teratoid rhabdoid tumors are rare, and it was not possible to identify significant risk factors of a worse prognosis, although the findings are in agreement with reports in the literature that such tumors affect younger children (< 1 year of age) and have a poor prognosis regardless of the treatment instituted.