Consistent with the effects on HRCA-PDOs, metformin treatment led to significantly decreased mRNA expression of adenoma stemness markers Lgr5 and c-Myc (Fig. 6K, left) and fast proliferation marker Ki67 (Fig. 6L, right), confirming that metformin prevented CA development through restricting the stemness maintenance of AOM/DSS-induced adenoma. Here, MKI67 is linked to infectious otitis media.