Discussion
tumor, non-tumor, cancers [Primary tumor, CRC
TUMOR, TUMOR RECURRENCE, MUTANT, PERITONEAL DISSEMINATION, SOMATIC MUTATIONS
In this prospective study, we reported that peritoneal cfDNA in lavage fluid by ultradeep NGS was a reliable tool for detection of PM in CRC with high sensitivity and specificity. High concordance of genetic mutational profiling and driver genes were observed between peritoneal cfDNA and tumor tissue of CRC patients. The clinical utility of peritoneal cfDNA was proven in the validation cohort. Therefore, the importance of peritoneal cfDNA as a liquid biopsy proves to be a surrogate or adjuvant biomarker instead of laparoscopy for earlier diagnosis of PM.Early detection of PM in CRC is a difficult clinical issue. CEA is current tumor biomarker in detection of tumor recurrence, but is limited by low sensitivity and specificity [Currently, interest has developed in the usage of liquid biopsy for cfDNA in early detection of cancers [Primary tumor shed cfDNA into the circulation, and the concentration of plasma cfDNA is relatively high for metastatic or recurrent CRC [To our knowledge, this is the first study to report peritoneal cfDNA for detection of CRC with PM. Peritoneal fluids are not common in CRC with early PM. Thus, we have conducted this cfDNA assays by peritoneal lavages. High similarity of gene mutations between peritoneal lavage and tumor tissue were shown in PM. Thus, mini-invasive peritoneal cfDNA could reflect tumor mutant burden and molecular features of PM instead of invasive test by tumor tissue. Ultradeep NGS can overcome the limitations of shallow sequencing depth of NGS profiling to achieve high sensitivity similar to ddPCR that is restricted to specific hotpot mutations [Peritoneal FLD and matched TIS are set to decrease false-positive germline variants and identified tumor-derived mutations of cfDNA to filter out background signal that comes from non-tumor-derived mutations. Matched cfDNA-WBC sequencing is usually applied in plasma cfDNA studies to exclude non-tumor derived cfDNA from clonal hematopoiesis in the blood [High concordance of driver genes in peritoneal lavage and tumor tissues are identified in this study. Despite the clinical values of our results, several limitations are still existing in this study. Firstly, this is a prospective diagnostic study with small sample size from one single institution. Our promising findings require to be verified in large cohorts of PM from multi centers. Secondly, although cfDNA experimental personals are blinded while clinicians know the diagnosis, selection of patients can still introduce bias. It is perfect if clinicians are blinded and they found peritoneal cfDNA without knowing intraoperative findings. In addition, patient population is heterogeneous as some of them received preoperative treatment which may impact some results. Thirdly, matched plasma cfDNA from WBC was used to match tumor tissue DNA to filter out somatic mutations.In conclusion, our data show that peritoneal cfDNA detected using ultradeep NGS is a potential sensitive and reliable biomarker for detection of PM in CRC patients. It offers a minimally invasive tool for assessment of driver gene mutations to guide selection of candidate patients for targeted therapies. Peritoneal cfDNA can predict the prognosis of PM and serve as a potential surrogate or adjuvant biomarker in active postoperative surveillance of peritoneal dissemination in high-risk CRC patients instead of laparoscopic explore.