Although magnifying endoscopy with narrow-band imaging (ME-NBI) has been widely used for qualitative diagnosis, such as differentiating cancerous lesions from non-cancerous lesions and predicting histology, its usefulness for assessing invasion depth remains unclear. Previous studies have mainly focused on the demarcation line and microvascular or microsurface patterns for qualitative diagnosis, whereas evidence regarding ME-NBI findings associated with submucosal invasion is still limited. The purpose of this study is to investigate which ME-NBI findings could be useful for diagnosing the invasion depth of gastric cancer.

A total of 255 gastric cancer lesions resected by endoscopic submucosal dissection (ESD) were retrospectively analyzed, including 174 mucosal (M) and 81 submucosal (SM) cancers. ME-NBI findings were reviewed to assess the following features:

1. Presence of RAC (Regular Arrangement of Collecting Venules)-like vessels
2. Cyan-colored and thick vessels
3. Disruption of the microvascular pattern (MVP)
4. Loss of the microsurface pattern (MSP)

The diagnostic performance of each finding for predicting SM invasion was evaluated by calculating sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), and negative likelihood ratio (NLR).

Diagnostic performance (sensitivity / specificity / PPV / NPV / PLR / NLR) was as follows:

1. Presence of RAC-like vessels: 90.0% / 74.4% / 62.0% / 93.5% / 3.6 / 0.13
2. Cyan-colored and thick vessels: 44.4% / 95.3% / 76.6% / 78.4% / 9.4 / 0.58
3. Disruption of MVP: 35.8% / 96.0% / 80.6% / 76.3% / 8.8 / 0.67
4. Loss of MSP: 39.5% / 83.9% / 53.3% / 74.9% / 3.3 / 0.71

The presence of cyan-colored vessels and disruption of MVP were strongly associated with SM invasion. The NLR of RAC-like vessels was low, suggesting that the absence of RAC-like vessels indicates a low probability of submucosal invasion.

Among ME-NBI findings, the presence of cyan-colored vessels and disrupted MVP are useful indicators suggesting submucosal invasion in gastric cancer. These findings may contribute to more accurate endoscopic assessment of invasion depth prior to ESD.