Clinical Report: Histological Representativeness of Glioblastoma Tissue Samples

Overview

Glioblastomas exhibit extensive histopathological heterogeneity, complicating the retrieval of representative tissue samples for diagnosis. This study assessed the relationship between the amount of viable tissue on hematoxylin-eosin slides and the presence of key histological features in 106 GBM patients, highlighting the impact of tissue quantity on diagnostic accuracy.

Background

Glioblastomas (GBMs) are the most common and malignant primary brain tumors in adults, with a median survival of 10–14 months despite maximal resection and adjuvant radio-chemotherapy. GBMs are histologically heterogeneous, increasing the risk of sampling errors and undergrading on biopsies. Diagnosis relies on histological and molecular analyses per WHO classification, including IDH mutation status. However, comprehensive molecular diagnostics are not universally available, making histological representativeness critical for accurate diagnosis and research.

Data Highlights

The study included 106 adult patients with newly diagnosed GBMs, retrospectively selected based on MRI and histopathological criteria. Tissue amount on HE slides was semiquantitatively categorized as sparse, medium, or substantial, with viable tissue areas ranging from 32 mm² (sparse) to 279 mm² (substantial). Associations were assessed between tissue amount and 24 histopathological features, Ki-67/MIB-1 proliferative index, CD105 microvessel density, MRI volumetrics, surgical procedure type, number of slides, and estimated tissue volumes.

Key Findings

• GBMs show extensive histopathological heterogeneity, complicating representative sampling.
• Smaller volumes of viable tissue on HE slides correlate with lower detection rates of key histological features.
• The presence of mandatory grade IV features (microvascular proliferation and necrosis) depends on tissue amount, affecting tumor grading accuracy.
• Subjective categorization of tissue amount (sparse, medium, substantial) aligns with measurable viable tissue areas and influences histological assessments.
• Associations exist between tissue amount and MRI volumetrics, surgical procedure, and number of HE slides, impacting sample representativeness.
• Comprehensive molecular analyses improve diagnostic accuracy but are not widely accessible, emphasizing the importance of adequate tissue sampling.

Clinical Implications

Clinicians should be aware that limited viable tissue in GBM samples may lead to undergrading and misclassification, potentially impacting treatment decisions. Ensuring sufficient tissue quantity during surgical resection and biopsy is critical for accurate histopathological evaluation. Where molecular diagnostics are unavailable, maximizing histological representativeness remains essential for reliable diagnosis.

Conclusion

This study underscores the importance of adequate viable tissue sampling in GBM histopathology to reduce diagnostic errors due to tumor heterogeneity. Optimizing tissue amount on HE slides enhances the detection of critical histological features necessary for accurate tumor grading and classification.

References

1. Stensjøen et al. 2016 -- Preoperative growth dynamics of GBMs
2. WHO Classification of Tumors of the Central Nervous System 2016
3. Gutt-Will et al. -- Ellipsoid volume formula for tissue estimation