Germline Mutations Of PALB2 Gene In A Sequential Series Of Chinese Patients With Breast Cancer

Background and objectiveBreast cancer has become the most common invasive cancer type around global women,seriously affect the health and life of Chinese women,brings great pressure to social and public health.Especially for breast cancer,early screening,early diagnosis,early treatment,can effectively control the mortality rate.Among all breast cancer patients,about 10%-15%has a family or hereditary background,and breast cancer is one kind of tumors with strong genetic background.In the early years,western countries have carried out the research on the genetic background of breast cancer,in which the BRCA1 gene and BRCA2 gene are the earliest discovered and most important breast cancer susceptibility genes.After years of study,foreign or domestic research on BRCA1 gene and BRCA2 gene have got larger samples and sequencing data,and demonstrate the exact risk of these two genes on breast cancer prediction.Thanks to the development of the second generation sequencing,more breast cancer susceptibility genes have been found,including PALB2 gene（Partner and localizer of BRCA2）is a recently discovered susceptibility gene for breast cancer.When DNA injuried,PALB2 collaborative with BRCA1 and BRCA2 and RAD51 together to maintain genomic stability.Unlike the previous study believed that PALB2 gene mutation is morderate penetrance,latest date has confirmed that the incidence of breast cancer caused by pathogenic mutation of PALB2 gene is similar to BRCA2 gene pathogenic mutation.In Europe and the United States has listed PALB2 gene as a routine screening in patients with familial predisposition breast cancer.But in the China area,there are only two reports about PALB2 in recent two years.The sample size is small,and can not represent the overall population.The PALB2 gene mutation spectrum in Chinese porpulation is still unclear.Thus,it is in urgent need of a large number sample accumulation firstly.Germline utations in the PALB2 gene caused a loss of function,leading to an increased risk of breast cancer.MethodsOur study include two parts.The first part of this study was to screen the PALB2 susceptibility gene with breast cancer in our hospital.We used the second generation sequencing（whole exon sequencing）technology,take the patient’s peripheral blood samples,extracted gDNA,compared with the gene database,excluded single nucleotide polymorphism,then confiremed a clear mutation site.The clinical pathological features were analyzed.From October 2000 to October 2016,a total of 2303 cases of breast cancer patients’ blood samples were sequenced the exon and the classical splicing site.All patients were recorded with detailed pathological records and clinical treatment.The second part,compared to the ClinVar and dbSNP database,we interpreted the mutations site we found.In accordance with the ACMGguideline,we classified the de novo mutation and the varient uncertain significance（VUS）mutaionResultsPart one study:Finally,we got a total of 2279 cases of breast cancer patients with PALB2 gene mutation data,of which 307 cases had a family history of breast cancer,and sporadic breast cancer in 1972 cases.A total of 5.92%（n=135）patients with PALB2 gene mutations were found,of which,119 patients had single PALB2 gene mutation,and the rest 16 patients had mutations partener with the BRCA1 gene or BRCA2 gene.PALB2 gene mutations accounted for 7.8%（n=24）in familial breast cancer,accounting for 4.5%（n=95）in patients with sporadic breast,there was a significancer difference（p<0.012）.In carried of PALB2 gene mutation in breast cancer patients,breast cancer molecular subtype distribution is Luminal A=22 cases（18.49%）,LuminalB=37（31.09%cases）,TNBC=16（14.45%cases）,Her2（36.97%）=44 cases.Opposite,non-carriers’ molecular subtype is Luminal A=520 cases（24.25%）,LuminalB=868（40.49%cases）,TNBC=373（17.40%cases）,Her2（17.86%）=383 cases,the molecular type distribution between the two groups had significant difference（p<0.001）.There were 31 kinds of missense mutations,4 kinds of nonsense mutations,3 kinds of frameshift mutaions,3 kinds of splicing site mutations,1 kind of codon mutation.The second part studiesIn all the mutations,5 kinds of mutaion have confirmed by the previous data as clear pathogenic mutations（Pathogenic）（c.751 C>T,c.1059delA,c.2323C>T,c.3256C>T,c.3507₃508delTC）,7 kinds of mutaions as clinical significance is unknown（VUS）mutations（c.1054G>C,c.1987C>T,c.2058G>T,c.2273C>G,c.2289G>C,c.2360C>T,c.3296C>T）.4 kinds of evidence conflict（Conflic）mutations（c.1273G>A,c.1492G>T,c.1955G>A,c.3054G>C）,the remaining 24 kinds of mutations were first discovered mutations.This study also conducted a follow-up analysis for the new found mutations,according to the ACMGguideline classification method based on evidence.The pedigree of patients were draw,and the relative were sequenced.We found and identified 6 kinds of pathogenic mutations,18 kinds of varient uncertain significance.We will continue to improve the PALB2 gene screening database.ConclusionOur data reveal the occurrence of germline mutations in the PALB2 gene in Chinese breast cancer patients,suggesting that PALB2 gene germline loss of functional mutation plays a certain role in the pathogenesis of hereditary breast cancer,and will make impact on breast cancer molecular typing.But we still need further data for verification.Our study found and identified new pathogenic mutations,and added evidence to the varient uncertain signifcance mutaions.The data of this study provide support for genetic counseling in Chinese breast cancer patients carring PALB2 mutaions.Also provide a pre theoretical study for the clinical management of patients with PALB2 gene mutations.