Phiroz Tarapore, Department of Neurosurgery, University of California, San Francisco, USA, and others reported in Neurosurgery that grade I spinal ependymomas are associated significantly lower rates of progression-free survival compared with grade II—which contradicts the World Health Organization (WHO)’s grading system for the tumours.
Tarapore et al reported that WHO classifies ependymomas into grade I, II, or III tumours—grade I being the least aggressive and grade III being the most aggressive. However, the authors commented that there is evidence that intracranial (90% of ependymomas in the paediatric population are intracranial) and intraspinal (75% of ependymomas in the adult population are intraspinal) ependymomas tumours of the same histological type may have different biological properties. They added: “As a result, the pragmatic value of WHO grading scheme in terms of predicting outcome remains unclear for adult intraspinal ependymomas.”
The aim of their study was to determine progression-free survival and the importance of extent of resection in each grade of ependymoma.
After analysing all patients who underwent initial intradural spinal surgery for a tumour between 1985 and 2010 at the University of California, Tapapore et al identified 134 patients with an ependymoma. Of these, 30 had a grade I tumour, 101 had a grade II tumour, and three had a grade III tumour. The authors found that grade I tumours were mostly located in the lumbar region, grade II tumours were mostly located in the cervical and thoracic regions, and grade III (two of three) were mostly located in the lumbosacral region.
The average progression-free survival was six years with grade I ependymomas, 14.9 years with grade II ependymomas, and 3.7 years with grade III ependymomas (p<0.001). Therefore, while grade III ependymomas were associated with shortest progress-free survival (in line with the WHO grading system), grade II ependymomas were associated with a progress-free survival that more than double that of grade I ependymomas. Tapapore et al stated: “This difference ran counter to the classic assumption that increasing grade implies a more aggressive behaviour and therefore shorter time to recurrence or progression.”
Additionally, in patients with grade I tumours, there was no significant differences between those who underwent gross total resection and those who underwent subtotal resection. However, patients with grade II who underwent gross total resection had significantly greater progression-free survival compared with grade II patients who underwent subtotal resection (17.8 years vs. 11.2 years, respectively; p<0.01). There was an insufficient number of numbers in the grade III group to determine a difference between gross total resection and subtotal resection. Tapapore et al commented that a potential reason for the lack of difference in the resection approach observed in grade I patients is that in the patients who underwent gross total resection, it was performed in a piecemeal fashion. They explained: “It is possible that violating the tumour capsule disseminates tumour cells, thus reducing the advantages of gross total resection.” The authors added that there was insufficient data to determine if piecemeal vs. en bloc resection affected progress-free survival but said: “We do note that several of our recurrent grade I tumours occurred at the site of resection. Therefore, grade I ependymomas, much like other locally aggressive tumours, may be best controlled with en bloc resection.”
Concluding, the Tapatore et al wrote: “In grade I and grade II ependymomas, there is an apparent discrepancy between WHO grading scheme and observed progression-free survival—contrary to their higher grade, WHO grade II ependymomas seem to carry a better progression than grade I ependymomas.”