MSH2 and Lynch syndrome: Case reports have documented mosaic MSH2 mutations in Lynch (-like) syndromes—for example, Erell Guillerm et al. detected a low-frequency MSH2 mutation in tumor tissue but absent in blood, which was confirmed as germline mosaicism in her daughter (Guillerm et al., 2020), while Pastrello et al. described somatic mosaicism with uneven mutation distribution across tissues (Pastrello et al., 2009).