To define the earliest PanIN, we performed an optic‐clear 3D histological analysis of the entire pancreas in 2‐week‐old Pdx1‐Cre; LSL‐Kras+/+ (control) and Pdx1‐Cre; LSL‐KrasG12D/+ (KC) mice using an aqueous solution called RapiClear (Figures S1 and S2A, Supporting Information). Here, KRAS is linked to keratoconus.