Analysis of Japan's national disease registry identified pseudo-polyps as tripling colorectal cancer risk in ulcerative colitis patients (hazard ratio 2.92), while abnormal crypt architecture increased risk by 3.14-fold and dysplasia by an alarming 11.31-fold. Among 78,556 UC patients tracked over nearly a decade, 141 developed colorectal cancer, with peak incidence occurring surprisingly in the 25-39 age group rather than older demographics. This finding challenges conventional assumptions about UC-related cancer timing and suggests younger patients with inflammatory bowel disease require more aggressive surveillance than current protocols recommend. The protective effect of 5-ASA treatment (64% risk reduction) reinforces the importance of consistent anti-inflammatory therapy, though the mechanism remains unclear. Machine learning stratification revealed that extensive colitis involvement dramatically elevates cancer risk compared to limited disease. These results fill a critical gap in Asian population data, as most UC cancer research derives from Western cohorts with different genetic and environmental backgrounds. The study's strength lies in its population-scale approach, though longer follow-up periods would better capture the full cancer development timeline in this chronic inflammatory condition.