**6. The role of biopsy in diagnosis**

Prior to the routine MRI use, it was estimated that up to 15% of patients diagnosed with DIPG had a non-glial tumor or non-tumor process [41, 42]. The role of surgical intervention was controversial and, in some centres, biopsy procedures were frequently undertaken for histological confirmation. Although it is not 100% specific, with the wide availability in the early 1990s MRI became the modality of choice for DIPG diagnosis. Biopsy confirmation was thought to be an unnecessary risk as it did not alter the management [43]. The lack of clear biopsy benefit combined with improved diagnostic imaging capabilities led to MRI scans becoming the diagnostic standard of care for DIPG in the United Sates [18, 44]. More recently, there has been a renewed interest in performing stereotactic biopsies in patients with DIPG [45]. In France, biopsies were routinely performed with minimal morbidity and high diagnostic yield [46], nonetheless, it was not a common practice. The increase in the available DIPG tumor samples has yielded valuable data toward improving our understanding of the biology of DIPG [45, 47, 48]. Some of the identified biologic markers have been shown to correlate with progression-free survival (PFS) and may be useful to stratify patients in future clinical trials [49]. Considering the potential for new diagnostic and therapeutic methods combined with low morbidity associated with surgical procedures [50], the option of biopsy is being reconsidered and may eventually be included as part of the routine diagnostic evaluation for DIPG [51]. The second Consensus Conference on Pediatric Neurosurgery recommended biopsy in DIPG to ascertain biological characteristics to enhance understanding and targeting of treatment, especially in the setting of clinical trials [52]. Biopsy from a single area may not be representative of the entire tumor [53] but it may still provide important molecular information.

## **7. Treatment**

More than 250 clinical trials in the last three decades have failed to improve the poor outcome of DIPG [20]. Due to the location it is not amenable to the surgery and chemotherapy agents are yet to show any response. Radiation therapy remains the standard of care at present. The barriers to achieve a cure for DIPG may include the inability of the surgical resection, drug delivery difficulties secondary to the blood-brain barrier (BBB) and intra- and inter-tumoral heterogeneity in the identified molecular aberrations [54].

#### **7.1. Surgery**

**Figure 2.** Histologic features of DIPG. Tumor infiltrating medullary neurons, H & E 100× (A) and 200× (B). (C) Tumor showing mitotic figures, H & E 400×. (D) Tumor/necrosis interface showing pseudo-palisading tumor necrosis. (E) Exuberant tumor-associated microvascular proliferation. (F) Tumor cells showing positive nuclear H3K27 M staining with sparing of the endothelial nuclei of admixed blood vessels H3K27 M 200×. (G) Loss of staining of tumor cell nuclei with the trimethylated antibody with retained staining in the endothelial cells, H3K27me3 200×. Images courtesy of Dr.

Jason Dyke (Royal Perth Hospital, Australia).

40 Brain Tumors - An Update

Surgical resection of DIPG is not feasible due to the presence of vital structures where the tumor is located. Rarely, surgical intervention like ventriculoperitoneal shunt or endoscopic third ventriculostomy may be necessary to relieve raised intracranial pressure secondary to hydrocephalus. Many patients benefit from steroids which help by reducing peritumoral edema.

responsible for repair of N7

EGFR expression status [66].

showed similar poor results.

(allograft and xenograft) [73–75].

**8.1. Cell of origin**

ullary nestin<sup>+</sup>

**8.2. The genomic landscape**

sion and chromosomal number changes.

**8. Biology**


tion of topotecan with RT was found to be ineffective [67, 68].

regulation may play a role in TMZ resistance in DIPG [65]. A recently closed phase II study stratified patients to receive TMZ and erlotinib based on MGMT methylation and

**ii.** Topotecan: topotecan acts as a radiosensitizing agent by stabilizing the DNA topoisomerase I complex, interfering with DNA replication and DNA repair. Concurrent administra-

**iii.** Other radiosensitizing agents like motexafin-gadolinium [69] and carbogen [70] also

More than 250 therapeutic clinical trials including several targeted agents have not improved the dismal prognosis of DIPG [10]. The reason for this, at least in part, has been attributed to our lack of understanding of the biology of this disease. More has been published on the biology and pathophysiology of DIPG in the past 10 years than in all prior years combined [5]. A more recent and significant achievement in DIPG research is sample collection at autopsy. This has provided invaluable insights into understanding of the biology [71, 72]. Both autopsy and biopsy samples have allowed development of *in-vitro* (neurospheres) and *in-vivo* models

Pontine precursor-like cells (PPC), found in the ventral pons region, which are positive for the markers for the primitive neural precursor cells, nestin and vimentin, are postulated as the candidate cell of origin for DIPG [35]. Approximately half of PPC also expressed Olig2, a transcription factor which is associated with oligodendroglial precursors. This cell type was morphologically distinct from the nestin positive cells seen in the dorsal brainstem. PPC are present in all ventral brainstem structures during infancy and wane by 2 years of age. The ventral pontine and med-

DIPG. Thus, temporal and spatial distribution of these cells correlates closely with the incidence of DIPG suggesting that tumors arise secondary to dysregulation of a postnatal neurodevelopmental process [35]. Expression of SOX2, a transcription factor with activity during embryogenesis, and Olig2 in another model supports the disordered neurodevelopmental origin of DIPG [76].

DIPG biopsy and autopsy samples have undergone extensive genomic profiling and major breakthroughs have been achieved in identifying key oncogenic pathways [77]. The drivers for DIPG tumorigenesis include epigenetic changes, gene mutations, deletions or overexpres-

cells show a second peak at 6 years, corresponding to the age of presentation of


http://dx.doi.org/10.5772/intechopen.78578

Diffuse Intrinsic Pontine Glioma

43

#### **7.2. Radiation therapy (RT)**

Conventional RT in a dose of 54–60Gy over a 6 week period is commonly utilized in the treatment of DIPG [9]. Temporary improvement or stabilization of symptoms is seen in 70% of patients, but almost all patients have progressive disease. The mean progression-free survival (PFS) is 5.8 months with radiotherapy and 5 months without it [4]. As RT is effective temporarily, non-conventional doses and delivery schedules were investigated. In hyperfractionated RT, the total dose is divided into smaller doses and given more than once a day. Hyperfractionated RT in the form of 1Gy twice a day, to the total dose of 72Gy failed to improve the outcome [37]. Hypofractionated RT is given over a smaller period of time than standard RT by dividing the total RT dose into larger doses and treatments given once a day or less often. Studies investigating the role of hypofractionated RT with 39Gy [55] or 45Gy [56] delivered over 3 weeks have revealed similar survival outcomes, but may be more acceptable to fami9lies due to the shorter delivery times.

#### **7.3. Chemotherapy**

Various chemotherapy and targeted agents have been used to potentiate the beneficial effects of RT. These agents were combined before, with, and after RT without much success [9, 10].

#### *7.3.1. Intensive chemotherapy*

Chemotherapy combinations used with RT in the setting of phase I–III clinical trials. These include lomustine, vincristine and prednisone [41], cisplatin, etoposide, vincristine, ifosfamide and oral valproic acid [57], myeloablative thiotepa, isotretinoin and vinorelbine [58] and multiple other agents at relapse [59]. One trial evaluated the role of preradiation chemotherapy [60]. The outcome was uniformly poor.

#### *7.3.2. Radiosensitizing agents*

**i.** Temozolomide (TMZ): TMZ is an alkylating prodrug which is converted into its active metabolite monomethyl 5-triazeno imidazole carboxamide. TMZ causes DNA damage by alkylating O6 -guanine, N7 -gaunine and N<sup>3</sup> -adenine resides [61]. Due to its proven efficacy in high grade gliomas, low toxicity and radiosensitization potential, temozolomide was trialed to potentiate RT efficacy without much success [8, 62, 63]. Addition of lomustine to adjuvant temozolomide [64] was not beneficial. O6-methylguanine DNA methyltransferase (MGMT) contributes to TMZ resistance by repairing alkylated O6 -guanine nucleotides. But this does not appear to be the cause of TMZ resistance as MGMT is not expressed in DIPG [47]. However, 3-methylpurine-DNA glycosylase (MPG), enzyme responsible for repair of N7 -gaunine and N<sup>3</sup> -adenine nucleotides, and its ATM-dependent regulation may play a role in TMZ resistance in DIPG [65]. A recently closed phase II study stratified patients to receive TMZ and erlotinib based on MGMT methylation and EGFR expression status [66].

