However, most commonly, MMR deficiency is an early event in tumor formation and promotes the development of precursor lesions termed MMR-deficient crypt foci (MMR-DCF), which can progress either through a non-polypoid adenomatous phase (second type of carcinogenesis) or lead directly to invasive cancer (third type of carcinogenesis), which is why colonoscopy alone does not currently seem to be sufficient for early diagnosis [40] (Figure 2). The gene discussed is MRC1; the disease is hyperinsulinemic hypoglycemia, familial, 4.