Approaches for Lynch syndrome screening and characteristics of subtypes with mismatch repair deficiency in patients with colorectal carcinoma.

To evaluate different Lynch syndrome (LS) screening approaches and establish an efficient and sensitive strategy are critical for clinical practice. In total, 583 patients with colorectal carcinoma (CRC) at Fudan University Shanghai Cancer Center were enrolled. Patient samples were examined by immunohistochemistry (IHC) and next-generation sequencing (NGS), and MLH1 promoter hypermethylation (MPH) was detected in MLH1-deficient cases. Germline genetic testing was performed in cases with deleterious variants and large genomic rearrangements (LGRs) of tumor MMR genes were detected in cases with dMMR or MSI-H cases with no MMR germline variants. Our results showed that triage with IHC and followed by BRAF/MLH1 methylation testing (Strategy 1) identified 93.3% (70/75) of LS cases. IHC followed by germline NGS (Strategy 2) or direct tumor NGS (Strategy 3) both identified 98.7% (74/75) of LS cases. The proportion of LGRs in LS cases was 16.0% (12/75), while 84.0% (63/75) showed SNV/Indel. The average cost per patient was ¥6010.81, ¥6058.48, and ¥8029.98 for Strategy 1, Strategy 2 and Strategy 3, respectively. The average time spent on different strategies was 4.74 days (Strategy 1), 4.89 days (Strategy 2), and 14.50 days (Strategy 3) per patient, respectively. LS and Lynch-like syndrome (LLS) were associated with an earlier onset age than MPH. In conclusion, we compared different workflows for LS screening and IHC plus germline NGS is recommended for LS screening when taking sensitivity, time, and cost into account. Moreover, multiplex ligation-dependent probe amplification made up for the shortcoming of NGS and should be incorporated into routine screening.