Pseudoprogression and Neurologic Deterioration

critical, because true progressors require a change in treatment, but pseudoprogressors should continue with adjuvant temozolomide. Currently, there are no definitive radiologic criteria to differentiate between true progression and pseudoprogression. The response criteria for brain tumours developed by the Response Assessment in Neuro-Oncology Working Group state that apparent radiologic progression can be considered true progression within 12 weeks of completion of chemoradiotherapy only if new lesions have appeared outside the radiation field or if pathology confirmation of progressive disease has been obtained7. Histopathology might assist in making the differentiation, but the analysis can be challenging, because specimens may contain viable tumour, necrosis, a mixed infiltrate of acute and chronic inflammatory cells, and edema8. Hence, given the high incidence of pseudoprogression and the absence of definitive radiologic criteria, it is impractical to subject all such patients to surgery, particularly if they are clinically stable. Therefore, the distinction between true progression and pseudoprogression is made retrospectively by comparing the first post-chemoradiotherapy mri with subsequent imaging. Canadian gbm treatment guidelines recommend that 3 cycles of adjuvant temozolomide be given before a decision is made about whether the initial imaging changes represent true disease progression or pseudoprogression9,10. In the absence of definitive radiologic criteria or histopathologic diagnosis, an enlarging lesion within the radiation field on the first post-chemoradiotherapy mri presents a diagnostic dilemma to the oncologist. As a result, oncologists often look for other clues to help differentiate between true progression and pseudoprogression. One such example is the presence of neurologic deterioration at the time of the first post-chemoradiotherapy mri. Intuitively, it is logical that, in a patient with a radiologically enlarging lesion, worsening neurologic function is more likely to be associated with true disease progression. That ABSTRACT