Extent of resection as a prognostic variable in the treatment of gliomas.

The published neurosurgical literature remains unclear as to whether the extent of surgical resection statistically correlates with survival. The possible sources of this current state of confusion and lack of concordance between studies are numerous: different distributions of covariates, different classification criteria, differences in patient selection, and various methodological flaws. Almost all of the modern studies are retrospective and thus subject to numerous sources of bias and variation. Additional retrospective studies and poorly designed prospective studies will not clarify the effect of extent of surgery on survival. In the absence of randomized experiments with well-defined protocols for aggressive and conservative surgery, well-planned and carefully executed prospective observational studies are needed. In the meantime, we are left with the conclusion that little scientifically credible evidence is available to support the assertion that aggressive surgical resection prolongs survival.