KRT20 (keratin 20) is a structural protein that maintains keratin filament organization in intestinal epithelia 1. When phosphorylated, it plays a role in mucin secretion in the small intestine. Beyond normal epithelial function, KRT20 serves as a marker of differentiated cells in colorectal cancer, with KRT20+ cells representing post-mitotic progeny that can revert to cancer stem cells after therapeutic ablation 2. KRT20 expression patterns have significant clinical implications across multiple cancer types. In head and neck squamous cell carcinoma, KRT20 overexpression increases migration and invasion capacity and correlates with lymphatic metastasis and poor prognosis 3. In bladder cancer, high KRT20 expression combined with low KRT5 expression identifies aggressive luminal subtypes with worse recurrence-free and progression-free survival 45. High KRT20-expressing tumors are enriched for aggressive urothelial variants including micropapillary and plasmacytoid subtypes 5. In colorectal carcinoma, KRT20 loss correlates primarily with microsatellite instability-high status 1. KRT20 mRNA detection in peritoneal lavage fluid shows promise as a predictor of gastric cancer recurrence 6. In interstitial cystitis, reduced KRT20 expression distinguishes Hunner-type from non-Hunner-type disease 7.