Fig. 2

Histopathological features and invasion patterns of colorectal cancer. (a) Gland formation rate > 95%, good cell polarity, mild nuclear atypia, consistent with WHO Grade 1 differentiation; (b) approximately 70% gland formation, local stromal infiltration, increased mitotic figures (5–10/HPF), consistent with WHO Grade 2 differentiation; (c) gland formation < 50%, tumor cells arranged in solid sheets, increased nuclear-to-cytoplasmic ratio, pathological mitosis observed, consistent with WHO Grade 3 differentiation; (d) tumor cells penetrating vein wall with broken elastic fibers; (e) tumor cells encasing nerve bundles with disrupted perineurium; (f) EnVision staining for cytokeratin, discrete tumor cell clusters (≥ 5 cells/cluster) observed at the invasive front within red circle, meeting BD2 budding grade.