FFPE DNA Quality Assessment Protocol

We selected the FFPE specimens by applying a multiplex PCR assay^{59 (link),60 (link)} to define the quality of the DNA extracted from the FFPE samples. This assay uses primer sets that amplify four genomic fragments (100, 200, 300, and 400 bp); the names and sequences of the primers are provided in Supplementary Table 3. Before the multiplex PCR assay, the DNA sample was heated at 90 °C for 60 min to facilitate the removal of the crosslinks of the FFPE tissues, and FFPE DNA repair was performed by adding 1× ThermoPol Buffer, 50x dNTPs/NAD + mixture, and PreCR Repair Mix (NEB) for 30 min at 37 °C^{57 (link)}. The samples producing 300- and 400-bp fragments were deemed to be good quality and were selected for this study. Ultimately, 29 cases of FFPE IMPC passed the quality control test.