Introduction
Pineal anlage tumor (PAT) is an extremely rare histological diagnosis first described by Schmidbauer et al. [
1], not yet defined as a distinct tumor type in the most recent WHO classification of tumors of the central nervous system [
2,
3]. Since the WHO classification of 2007, PAT is described as a rare variant of pineoblastoma with melanotic, cartilaginous and/or rhabdomyoblastic differentiation [
4‐
6]. Histologically, this primary pineal tumor is characterized by heterogeneous elements of neuroepithelial and ectomesenchymal tissue, but without endodermal structures [
1]. They are similar to retinal anlage tumor of the jaw, which led to its terminology [
1,
7]. These tumors are thought of as highly aggressive and are associated with poor prognosis [
8]. However, assumptions have been made that there are tumors which meet some characteristics of PAT, while lacking primitive features [
8,
9].This led to the proposal to differentiate such tumors from the initially described tumors by Schmidbauer et al., because the latter tumors might require different adjuvant therapy strategies [
8].
Overall, due to the rarity of this tumor type, reported treatment strategies are diverse and the ideal strategy e.g. using pineoblastoma protocols remains unclear [
5].
Here, we report on three unpublished cases of tumors histologically classified as pineal anlage tumor and reviewed the literature focusing on clinical features and treatment.
Patients and methods
Data of 3 patients with pineal anlage tumor treated in Germany from 2000 to 2020 were complied. This study was performed in line with the principles of the Declaration of Helsinki and from all three patients, written informed consent was obtained from patients, parents, or legal guardians for publication of their data.
DNA methylation profiling and panel sequencing was performed as part of clinical routine or relapse work-up. The Heidelberg Brain Tumor Classifier Version v12b5 (
www.molecularneuropathology.com) was used for tumor classification by methylation. Next generation panel sequencing was performed analogous to procedures described by Sahm et al. [
10]. Simultaneously, DNA was also derived from blood to match results with germline information.
In addition, a literature review via Pubmed.gov using “pineal anlage tumor” and “pineal” as search terms on June 9th 2022 was performed and 17 further cases of PAT were identified. For these cases, reported clinical details were analyzed in detail.
Data of the cases are summarized in Table
1. Statistical analyses were explorative and were performed using IBM
© SPSS® Version 25. Kaplan–Meier method was used for survival estimation.
Table 1
Detailed overview of all published cases of pineal anlage tumor including 3 new cases from Germany
Discussion
This project aimed at evaluating treatment strategies for PAT. As these tumors histologically can be clearly distinct from other pineal region tumors, the question is, whether these tumors should be treated similar to other pineal region tumors e.g. pineoblastoma. As specific risk-adapted treatment strategies for specific molecular pineoblastoma subgroups may be established in the future, it appears reasonable to independently analyze treatment strategies for PAT.
To date, most case reports focused on histological descriptions with frequently missing clinical details and short follow-up times. Furthermore, publication bias cannot be excluded. These conditions only allow for very limited statistical analyses and conclusions for treatment recommendations need to be drawn with caution.
Nevertheless, sharing information about the clinical presentation and disease course of pineal anlage tumor is important. Therefore, we summarized all published cases and their clinical information.
Pineal anlage tumor primarily mostly affects young children during the first years of life. Analogous to other childhood embryonal brain tumor entities as e.g. medulloblastoma, males are affected more often than females.
A detailed staging process including spinal MRI and CSF cytology should always be part of the initial clinical work-up of these patients as already suggested by Ajayi et al. [
5].
Radiologically, PATs are often of large size at first diagnosis and present with circulatory dysfunction of the cerebrospinal fluid and consecutive occlusive hydrocephalus. Furthermore, these tumors show heterogeneous enhancement. Using computer tomography, the tumor is hyperdense, often cystic or calcified. In MRI, the tumor is T1-iso- or hypointense and T2-isointense compared to the surrounding brain parenchyma, and shows diffusion restriction [
5,
8,
24].
Nevertheless to date, no specific radiological characteristics are described to identify PAT by MRI only [
5]. Therefore, upfront surgery with the aim to obtain a tissue-based diagnosis seems to be reasonable in pineal masses negative for germ-cell tumor markers AFP and beta-HCG as well as negative medical history of a trilateral retinoblastoma.
In the reported German cases, biological relationship to pineoblastoma (PIN MYC/FOXR2) was found. Apart from this, similarity regarding the methylation signature of choroid plexus tumor at initial diagnosis and medulloblastoma at relapse for one case was described by Lopez-Nunez et al. [
18] (case 7 of this series). In fact, further biological characterized cases need to be reported to draw a solid conclusion regarding the biology of pineal anlage tumor.
As pineal region tumors are challenging to resect, addressing a specialized neurosurgical center needs to be considered whenever possible. Maximal save resection should be strived for, since PAT seem to show a wide range of response to adjuvant therapy and small tissue samples might show a non-representative part of the tumor resulting in a false diagnosis [
5,
23]. Taking into account the high chance of recurrence, from the author`s point of view, adjuvant treatment is indicated for all affected patients: PFS and OS are not yet satisfying based on this small series.
Since radiotherapy—and especially CSI that is usually considered necessary to treat embryonal tumors of the CNS – is associated with neurocognitive sequelae, when used in very young patients, intensive intravenous chemotherapy appears to be a reasonable choice. In reported cases, treatment protocols for embryonal tumors (formerly “primitive neuroectodermal tumors”) or pineoblastoma were chosen.
In this series, two patients with non-metastatic PAT and good response to induction chemotherapy were treated with focal radiotherapy after HDCT and did not relapse within the observation period. Therefore, we believe that focal RT might be considered as an additional treatment modality in patients with localized disease even at young age > 18 months. However, present data indicate that pineal anlage tumor can spread along the CNS especially during relapse. Therefore, craniospinal irradiation seems reasonable for disseminated disease, when it is not contraindicated due to young age or other conditions.
On the basis of the reported experience, we developed a flowchart to help making therapeutic decisions in these rare cases (Fig.
3). However, the optimal dose prescription and schedule within the multimodal treatment concept is still unclear and should be oriented to the recommendation and experiences of other embryonal CNS tumors in young children. Further, against the background of potential biological relationship to pineoblastoma and the fact that established treatment strategies for pineoblastoma / embryonal brain tumors appear to be efficient also in PAT, one may also discuss to follow national and international guidelines for pineoblastoma. Still, as specific treatment strategies may emerge for specific molecular subgroups of pineal region tumors, it appears reasonable to consider PAT also independently.
Finally, more knowledge needs to be obtained regarding the clinical presentation, molecular characteristics and treatment strategies of pineal anlage tumor to develop solid treatment guidelines. Therefore, we would like to encourage clinicians to share their experiences with patients suffering from rare tumors like pineal anlage tumor.
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