Number/quality of endoscopic biopsy samples in gastrointestinal cancers for biomarker testing: All that glitters is not gold

Background: Management of gastrointestinal (GI) cancers has shifted from conventional chemotherapy to biomarker-based precision oncology. Biomarker assessment requires adequate endoscopic biopsy tissue both in gastro-esophageal/gastric and colorectal carcinomas. Aims: This study evaluated real-world endoscopic biopsy adequacy, focusing on tissue quality and suitability for biomarker analysis. Methods: We retrospectively reviewed 819 endoscopic procedures (274 upper-GI and 545 lower-GI; time-window: January 2021-2024). Gastrointestinal pathologists reviewed 4,908 biopsies to assess diagnostic yield, number of invasive carcinoma-containing biopsies, and tumor cellularity. Biopsy adequacy was evaluated against European Society of Gastrointestinal Endoscopy (ESGE) recommendations and biomarker-specific cellularity thresholds. Results: A histologic diagnosis of invasive carcinoma was established in 96 % of upper-GI and 84 % of lower-GI procedures (p<0.001). However, 41–43 % of procedures yielded fewer than six biopsies, which is below ESGE guidance. Importantly, only 66.7 % of upper-GI and 49.7 % of lower-GI biopsies contained invasive carcinoma, while the rest were composed of samples inadequate for biomarker testing (such as non-invasive lesions, mucin, necrosis, granulation tissue, and normal mucosa). Low neoplastic cellularity (<1000 tumor cells) was observed in 27 % of upper-GI and 5 % of lower-GI cases, while <20 % tumor cellularity was present in 41.7 % of colorectal biopsies. Conclusion: Optimizing sampling strategies and ensuring representative, high-cellularity specimens are essential to support precision oncology in GI cancers.