Taken together, our study is one of the largest analyses of human MCN, highlighting: (i) mutational landscapes of tumor epithelium and corresponding adjacent tissue; (ii) intratumor heterogeneity; (iii) KRAS mutation abundance as a segregator between invasive cancers and preneoplastic lesions; and (iv) the presence and/or dosage of mutant KRAS as a driver of dysplasia. The gene discussed is KRAS; the disease is neoplasm.