Grade II gliomas include diffuse astrocytoma, oligodendroglioma, oligoastrocytoma, and ependymoma.
Diffuse Astrocytoma and Oligoastrocytoma (Grade II)
In general, these Grade II tumours are treated with surgical excision followed by consideration of radiotherapy.
Controversy - There is significant debate as to the timing of radiotherapy following surgical excision, either immediate or when the tumour progresses
This group of tumours has been the subject of three significant randomised controlled trials exploring the role of radiotherapy:
- EORTC 22844 trial; published in 1996. This trial compared two adjuvant regimes, 45 Gy in 5 weeks versus 59.4 Gy in 6 weeks. There was no difference in survival between the two arms. Tumour size was the most important prognostic factor.
- NCCTG trial; published in 2002. Similar to EORTC 22844, it compared two adjuvant regimes. 50.4 Gy/28 fractions was compared to 68.4 Gy in 36 fractions. There was a trend to poorer survival in the 68.4 Gy group and increased rates of radiation necrosis.
- EORTC 22845 trial; published in 2005. This study compared immediate adjuvant RT with delayed radiotherapy on progression. Dose was 54 Gy in 30 fractions. This study has fostered numerous arguments, as the findings included:
- No difference in overall survival (about 7 years median overall survival)
- Improved progression free survival in the immediately treated group (3.4 years in untreated, 5.3 years in treated)
- Improved seizure control at 1 year in the immediately treated group.
The EORTC 22845 study is used by supporters of both approaches to promote their views. Believers in early irradiation cite the improved local control rates and reduced seizure rates. Opponents cite the similar overall survival and claim that salvage radiotherapy is just as effective.
Observation
Observation is a viable option for asymptomatic patients of a young age with small tumours. Regular MRI scans should be performed with treatment offered at the time of progression.
Observation is not a good option for:
- Older patients (over 40)
- Symptomatic patients
- Patients with diffuse astrocytoma
- Tumours > 6 cm
Surgery
Surgery is usually recommended as 1/4 of radiological low-grade lesions are actually high grade on biopsy. Gross total resection is ideal if safe. If patients have subtotal resection then the case for further treatment is strengthened.
Radiotherapy
Radiotherapy is offered for patients with a combination of poor risk factors - these include age, sub-total resection, or diffuse astrocytoma pathology. The total dose should be between 50.4 and 54 Gy in 1.8 Gy fractions.
In patients who are observed after surgery, radiotherapy is offered when symptoms occur.
Chemotherapy for Oligodendroglioma
Oligodendrogliomas frequently contain loss of heterozygosity of 1p/19q. This feature makes them susceptible to procarbazine, lomustine, and vincristine (PCV). There is a growing evidence (although no randomised trials that I could find) that chemotherapy alone may delay tumour recurrence, allowing radiotherapy to be reserved for a later time.
The typical schedule is 4 cycles of PCV given at 6 weekly intervals.
