Importantly, the first model of colorectal carcinogenesis in LS patients is characterized by the growth of adenomas as tumor precursor lesions in an MMR-proficient background, but Sekine and colleagues suggest that MMR deficiency occurs in adenomas before the progression to carcinomas, emphasizing the relevance of MMR impairment during LS carcinogenesis [62]. The gene discussed is MRC1; the disease is adenoma.