http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3245992/Conclusion
Tumor pseudoprogression should be anticipated and not considered to be treatment failure. In our series, 23% of VS treated with radiosurgery underwent pseudoprogression, with onset at 6 months and, most commonly, regression by 24 months. VS that begin to enlarge only after 24 months are likely to be treatment failure, and a second intervention should be considered only at this stage.
In our series, there was no association between transient tumor enlargement and clinical deterioration. Therefore, we would advocate baseline imaging only to document the maximum stable size of VS after radiosurgery, and no salvage therapy should be instituted before 36 months, unless there is clinical need to intervene.
We did not identify any clinical or dosimetric parameters that could predict tumor pseudoprogression in our series. Further studies are required to understand the biological mechanisms of tumor pseudoprogression and to identify clinical predictors of this phenomenon.