Low-grade gliomas in children: tumor volume response to radiation

Radiation-induced astrocyte senescence is rescued by Δ133p53

BACKGROUND

Cellular senescence and the senescence-associated secretory phenotype (SASP) may contribute to the development of radiation therapy-associated side effects in the lung and blood vessels by promoting chronic inflammation. In the brain, inflammation contributes to the development of neurologic disease, including Alzheimer's disease. In this study, we investigated the roles of cellular senescence and Δ133p53, an inhibitory isoform of p53, in radiation-induced brain injury.

METHODS

Senescent cell types in irradiated human brain were identified with immunohistochemical labeling of senescence-associated proteins p16INK4A and heterochromatin protein Hp1γ in 13 patient cases, including 7 irradiated samples. To investigate the impact of radiation on astrocytes specifically, primary human astrocytes were irradiated and examined for expression of Δ133p53 and induction of SASP. Lentiviral expression of ∆133p53 was performed to investigate its role in regulating radiation-induced cellular senescence and astrocyte-mediated neuroinflammation.

RESULTS

Astrocytes expressing p16INK4A and Hp1γ were identified in all irradiated tissues, were increased in number in irradiated compared with untreated cancer patient tissues, and had higher labeling intensity in irradiated tissues compared with age-matched controls. Human astrocytes irradiated in vitro also experience induction of cellular senescence, have diminished Δ133p53, and adopt a neurotoxic phenotype as demonstrated by increased senescence-associated beta-galactosidase activity, p16INK4A, and interleukin (IL)-6. In human astrocytes, Δ133p53 inhibits radiation-induced senescence, promotes DNA double-strand break repair, and prevents astrocyte-mediated neuroinflammation and neurotoxicity.

CONCLUSIONS

Restoring expression of the endogenous p53 isoform, ∆133p53, protects astrocytes from radiation-induced senescence, promotes DNA repair, and inhibits astrocyte-mediated neuroinflammation.

Radiotherapy in the Management of Paediatric Low-Grade Gliomas

Paediatric low-grade (World Health Organization grade I-II) gliomas (LGGs) represent a spectrum of primary central nervous system tumours. Local tumour control is the cornerstone in the general management of childhood gliomas. Surgery is the primary treatment of choice in the majority. Non-surgical treatments are recommended for progressive or symptomatic inoperable disease. Although chemotherapy is increasingly used as first non-surgical treatment, radiotherapy remains standard as salvage treatment or as primary treatment in selected cases in which surrounding normal tissue can be optimally preserved. The role of targeted therapies is currently under investigation in clinical trials. Modern high-precision radiotherapy techniques, including proton therapy, have the potential to improve long-term toxicities. There is therefore an urgent need for prospective studies to compare the efficacy and safety of modern radiotherapy with systemic treatment in children with LGGs. New information on molecular genetic patterns in LGGs may also have an impact on the selection and sequencing of radiotherapy.

Outcomes of pediatric low-grade gliomas treated with radiation therapy: a single-institution study

Radiation therapy is often considered the treatment of choice for low-grade gliomas. However, given the long-term effects of radiation on the developing brain, the appropriate use of radiation therapy in pediatric patients remains controversial. The purpose of this study was to evaluate progression-free survival (PFS) of pediatric low-grade glioma patients treated with radiation therapy. Data were obtained through a retrospective chart review of patients treated between 1991 and 2008 from a single tertiary care center in the midwest. The study population consisted of 17 patients, of whom 8 (47%) had tumor recurrence after radiation therapy. The median follow-up time was 8.2 years, with a range of 2.3 to 17.2 years. The median age at diagnosis was 5.4 years, and the median age at radiation therapy was 9.4 years. The 3- and the 10-year PFS were 69%± 11.7% and 46%± 13.3%, respectively. A significant difference in PFS was seen when comparing brainstem tumors with hypothalamic/optic pathway tumors (P=0.019). Differences in PFS based on the age at diagnosis, the extent of initial surgery, and indication for radiation therapy were not significant. A larger multicenter study is needed to better assess PFS in these patients.

Vincristine and carboplatin chemotherapy for unresectable and/or recurrent low-grade astrocytoma of the brainstem

BACKGROUND

Radiotherapy remains a widely accepted postoperative treatment modality for unresectable or recurrent low-grade glioma (LGG). However, there is increasing evidence to suggest that chemotherapy can delay and may obviate the need for radiotherapy in progressive/recurrent LGG. The majority of the published experience is in children with hypothalamic/optic chiasmatic lesions and little information is available regarding its use in LGG of the brainstem.

PROCEDURE

We describe clinical characteristics and course of children with LGG of the brainstem who received carboplatin-based chemotherapy in two institutions over 10 years (1996-2006). This was a retrospective review of consecutively treated children with LGG of the brainstem (midbrain, pons, medulla, and upper cervical cord). Vincristine and carboplatin were first-line chemotherapy regimen used in all patients.

RESULTS

In this series, there were 16 children (9 males) with median age at diagnosis of 4.2 years (range 0.5-8). Eight children were treated at diagnosis while the remaining eight received chemotherapy after either radiological progression or clinical deterioration. After a median follow-up of 57 months (range 20-136) from initiation of chemotherapy all children are alive and 11 remain progression free (1 complete response, 8 with partial response + minor response, and 2 stable diseases).

CONCLUSIONS

The efficacy of this chemotherapy regimen in this series supports its role in children with progressive unresectable LGG of brainstem.

Factors associated with progression-free survival and long-term neurological outcome after resection of intramedullary spinal cord tumors: analysis of 101 consecutive cases

OBJECT

With the introduction of electrophysiological spinal cord monitoring, surgeons have been able to perform radical resection of intramedullary spinal cord tumors (IMSCTs). However, factors associated with tumor resectability, tumor recurrence, and long-term neurological outcome are poorly understood.

METHODS

The authors retrospectively reviewed 101 consecutive cases of IMSCT resection in adults and children at a single institution. Neurological function and MR images were evaluated preoperatively, at discharge, 1 month after surgery, and every 6 months thereafter. Factors associated with gross-total resection (GTR), progression-free survival (PFS), and long-term neurological improvement were assessed using multivariate regression analysis.

RESULTS

The mean age of the patients was 41 +/- 18 years and 17 (17%) of the patients were pediatric. Pathological type included ependymoma in 51 cases, hemangioblastoma in 15, pilocytic astrocytoma in 16, WHO Grade II astrocytoma in 10, and malignant astrocytoma in 9. A GTR was achieved in 60 cases (59%). Independent of histological tumor type, an intraoperatively identifiable tumor plane (OR 25.3, p < 0.0001) and decreasing tumor size (OR 1.2, p = 0.05) were associated with GTR. Thirty-four patients (34%) experienced acute neurological decline after surgery (associated with increasing age [OR 1.04, p = 0.02] and with intraoperative change in motor evoked potentials [OR 7.4, p = 0.003]); in 14 (41%) of these patients the change returned to preoperative baseline within 1 month. In 31 patients (31%) tumor progression developed by last follow-up (mean 19 months). Tumor histology (p < 0.0001) and the presence of an intraoperatively identified tumor plane (hazard ratio [HR] 0.44, p = 0.027) correlated with improved PFS. A GTR resulted in improved PFS for hemangioblastoma (HR 0.004, p = 0.04) and ependymoma (HR 0.2, p = 0.02), but not astrocytoma. Fifty-five patients (55%) maintained overall neurological improvement by last follow-up. The presence of an identifiable tumor plane (HR 3.1, p = 0.0004) and improvement in neurological symptoms before discharge (HR 2.3, p = 0.004) were associated with overall neurological improvement by last follow-up (mean 19 months).

CONCLUSIONS

Gross-total resection can be safely achieved in the vast majority of IMSCTs when an intraoperative plane is identified, independent of pathological type. The incidence of acute perioperative neurological decline increases with patient age but will improve to baseline in nearly half of patients within 1 month. Long-term improvement in motor, sensory, and bladder dysfunction may be achieved in a slight majority of patients and occurs more frequently in patients in whom a surgical plane can be identified. A GTR should be attempted for ependymoma and hemangioblastoma, but it may not affect PFS for astrocytoma. For all tumors, the intraoperative finding of a clear tumor plane of resection carries positive prognostic significance across all pathological types.

Pediatric low-grade gliomas

Pediatric low-grade gliomas encompass a heterogeneous set of tumors of different histologies. Cerebellar pilocytic astrocytomas occur most frequently followed by supratentorial diffuse fibrillary astrocytomas. Recent research has implicated activation of the RAS/RAF/MEK pathway in tumorigenesis of these tumors. Surgery is the mainstay of therapy. Overall survival rates for patients whose tumors are completely resected are 90% or greater, 10 years from diagnosis. Conversely, most optic pathway/hypothalamic, deep midline, and brain stem gliomas have minimal potential for resection; these tumors can be difficult to treat and deserve special attention. Combination chemotherapy is currently recommended as front-line adjuvant treatment for progressive or recurrent tumors. Second-line radiotherapy can also improve overall survival but is associated with more frequent and significant neurocognitive, endocrine, and other long-term toxicities.

Results of a policy of surveillance alone after surgical management of pediatric low grade gliomas

PURPOSE

To document the incidence of tumor progression in pediatric patients with low-grade gliomas (LGGs), with particular emphasis on those patients who did not receive postoperative chemotherapy or radiotherapy (RT).

METHODS AND MATERIALS

A database of 128 patients with histologically confirmed LGGs (World Health Organization Grade I-II), age <or=18 years, who had been referred to the London Regional Cancer Center and Dalhousie University between 1979 and 1995, was compiled.

RESULTS

The median follow-up for the 128 patients was 7.3 years. Of the 128 patients, 63 were male and 65 female. The median age was 7.0 years (range 0-18). Twenty-five patients underwent gross complete resection, 63 subtotal resection, and 40 patients biopsy. Ninety-one percent (n = 117) of the tumors were astrocytomas, of which 22 were pilocytic, 3 were oligodendrogliomas, 7 were mixed gliomas, and 1 was a ganglioglioma. Of the 103 subtotally resected patients, 48 received postoperative RT (median dose 59 Gy in 25 fractions) and 10 patients were irradiated at the time of tumor progression. The 5-year overall survival was 86%, cause-specific survival 88%, and 5-year progression-free survival 79%. The results of the univariate analysis of the overall survival by the Wilcoxon model were statistically significant for Karnofsky performance status (p = 0.03), RT timing (i.e., postoperative vs. deferred; p = 0.05), and tumor location (p = 0.02). The analysis of progression-free survival confirmed the statistical significance of the extent of surgical resection (i.e., complete vs. subtotal resection; p = 0.02). None of the patients who underwent gross complete resections received postoperative RT and none developed tumor recurrence. Of the 103 patients who had subtotal resections, 33 had progression, with a median postprogression survival of 39 months. The rate of tumor progression among the subtotally resected LGG patients who did not receive immediate postoperative RT was 42%. The timing of RT and tumor location lost statistical significance for overall survival when the completely resected patients were excluded from the analysis.

CONCLUSIONS

The extent of surgical resection was prognostically significant for progression-free survival but lost significance as a prognostic factor once the complete resection patients were excluded from the analysis. At a median survival of 7.3 years, 42% of the subtotally resected LGG patients who did not receive immediate postoperative RT had tumor progression. No statistically significant difference in survival was seen between the postoperative and deferred RT groups, even though the postoperative RT group was a group with poorer prognostic features (bulky residual tumor postoperatively, Karnofsky performance status <70, and nonhemispheric, noncerebellar tumors), indicating that RT may be beneficial for this particular subset of patients.