Innv-32. reliability of serial neuropathological assessment to differentiate tumor progression from pseudo-progression in glioma

Histopathology is the gold standard for distinguishing tumor recurrence from treatment-induced necrosis but differentiating pseudoprogression from true recurrence is challenging in tumors with ambiguous morphological features. Prior research reported a 36% inter-rater agreement during suspected recurrence (Holdhoff et al., 2019). While serial radiographic and laboratory assessments are common, serial histopathological assessments are not. This study evaluated agreement and factors influencing assessment of active and inactive tumors through single and multiple time-point histopathological assessments. Patients who underwent initial and subsequent reoperation were identified, and their available histology slides were examined retrospectively. Four independent neuropathologists conducted two types of reviews: single time-point reviews using most recent biopsy/surgery slides, and multiple time-point reviews comparing images from initial and repeat biopsies taken 1-3 months apart. Neuropathologists completed a questionnaire assessing various tumor characteristics. Assignments were categorized as "active tumor," "treatment effect," or "unable to classify." 324 assessments were conducted (108 single time-point, 216 multiple time-point). Intraclass correlation coefficients for single vs. multiple time-point assessments were 0.72-0.93 for active tumors and 0.57-0.86 for inactive tumors. Pathologists' assessment of % inactive tumor was influenced by mitotic activity (p= 0.0028), cellularity (p< 0.0001), hyalinized vessels (p= 0.0019), and necrosis (p= 0.0046). Evaluation of % active tumor was influenced by hyalinized vessels (p= 0.0006), mitotic activity (p< 0.0001), cellularity (p< 0.0001), and microvascular proliferation (p= 0.0093), with the latter three factors specifically affecting final sign-out pathology. Serial histopathological assessment didn’t affect determination of % active or inactive tumor. No association between % inactive tumor and fibrinoid necrosis for single time-point (p= 0.34) but a strong negative association was seen for serial assessment (p= 0.0006). Inter-rater agreement was higher for identifying active tumors than inactive tumors in both case reviews. Changes in necrosis between tissue samples in single vs. multiple timepoint assessments influenced pathologists' assessment of % inactive tumor.