Mutational Spectra Across Diverse Cancer By Using Plasma Circulating Tumor DNA Testing

Malignancy is a disease with multi-system disorder.As a result of interaction between sustained detrimental factors and disrupted inner protective system,cells present hallmarks of excessive proliferation,invasion and migration.Recently,recognition begins to prevail that tumor is a genetic disease as a consequence of “double or multi-hit”,promoting molecular characteristics-based drug research and development,clinical trials,basic research,and clinical guidance in making regimens.Tissue biopsy is the golden standard of determining molecular characteristics in clinical.Nevertheless,accumulating evidence show that tumor presents temporal and spatial heterogeneity.Published clinical datarevealthat tumor genetic aberrations indicating sensitive or resistant to on-label and off-label agents approved by FDA,and experimental drugs,are diverse,wherein they may occur in different genes,and in different loci of the same gene,or the same gene presents in different mutant types including point mutations,indels,copy number variations,and fusion.All the above pose a great challenge for tissue biopsy and the involved testing techniques.Liquid biopsy is one of representative diagnostic means in the era of precision medicine.With its high throughput and sensitivity,and flexibility in setting captured genes,targetcapture NGS(next-generation sequencing)has become the detecting technique of liquid biopsy.Besides the noninvasive property,NGS-based ctDNA(circulating tumor DNA)testing achieves comprehensive tumor mutational spectra dynamically.Up to now,released ctDNA data mainly focus on cancer with high morbidity,such as lung cancer,breast cancer,and intestinal cancer,while studies on cancer with a low prevalence are scarce.In our study,865 cases with various tumor types in middle-late stage received ctDNA testing.Among these,531 were thoracic malignancies(lung cancer,breast cancer,and others);208 weredigestive system ones(intestinal cancer,gastric cancer,liver cancer,esophageal cancer,pancreatic cancer,biliary cancer,and others);31 were gynecological ones(ovarian cancer,endometrial cancer,cervical cancer,and others);24 were genitourinary ones(renal cancer,bladder cancer,and others);16 were head and neck ones(thyroid cancer,nasopharyngeal cancer,and others);12 were reproductive system ones(prostate cancer,penis cancer,and others);and the rest 43 cases belong to other systems.Mutational spectra analysis across diverse cancer showed: 1)the detection rate across diverse cancer was different;2)point mutation and indels were the predominant type of mutation;3)almost all detected mutations were nonsynonymous;4)different tumor types both share the same common mutant genes,and have its specific ones;5)EGFR mutational spectra varied across diverse cancer and pathological subtypes;6)the number of mutation per sample was different across diverse cancer;7)the mutant allele frequency was different across diverse cancer;8)pathological germline mutation,such as BRCA1/2,presents in diverse cancer.This analysis revealed mutational spectra across diverse cancer,in particular providing guidance for the application of ctDNA in cancer with a low prevalence.On the other hand,through identifying their molecular profile,we explored the driver mutation occurring in early-stage cancer according to the “phylogenetic analysis”,thereby paving the way for cancer diagnosis in early stage.In addition,we tried to interpret the clinical applications of ctDNA.First,we identified whether the mutation impaired its corresponding protein and promoted the cancer development,and whether the patient carried mutation indicating sensitive or resistant to targeted drugs and targeted therapy is appropriate for the patient.Second,we calculated the patient’s tumor molecular burden according to the mutant allele frequency and the number of mutations,and speculated the clone which sensitive mutation belongs to.Through continuous monitoring,we knew the fluctuation of tumor burden and response to treatment.Therefore,patients with sensitive mutation in the main clone may benefit most from ctDNA testing,while the potential application in the population,such as without sensitive mutation,with many sensitive mutations coexisting,or with sensitive mutation belonging to subclone,was still investigated.Considering the big percentage of the population,recent investigations showed that immune system was associated with the tumor burden,and immunotherapy may open a novel modality for them.Therefore,we explored the potential clinical applications of ctDNA in multi-dimension,in hope of providing some clues for immunotherapy.