Germline Mutation Analysis in Sporadic Breast Cancer Cases with Clinical Correlations

Abstract

Demographics for breast cancers vary widely among nations. The frequency of germline mutations in breast cancers, which reflects the hereditary cases, has not been investigated adequately in Pakistani population. In the present study, germ-line mutations in twenty-seven breast cancer candidate genes were investigated in eighty-four sporadic breast cancer patients along with the clinical correlations. The germ-line variants were also assessed in two healthy controls. The most frequent parameters associated with hereditary cancer cases are age and ethnicity. Therefore, the clinico-pathological features were evaluated by descriptive analysis and Pearson χ2 test (with significant p-value <0.05). The analyses were stratified on the basis of age (<40 years vs >40 years) and ethnicity. The breast cancer gene panel assay was carried out by a genomic capture, massively parallel next generation sequencing assay on Illumina Hiseq2000 assay with 100bp read lengths. Copy number variations were determined by partially-mapped read algorithm. Once the mutation was identified, it was validated by Sanger sequencing. The ethnic analysis stratified on the basis of age showed that the frequency of breast cancer at young age (<40 years) was higher in Sindhis (n=12/19; 64%) in contrast to patients in other ethnic groups. Majority of the patients had stage III (38.1%), grades II and III (46.4%), tumor size 2-5cm (54.8%), and invasive ductal carcinoma (81%). Overall, the analysis revealed germ-line mutations in 11.9% of the patients. The mutational spectrum was restricted to three genes: BRCA1, BRCA2, and TP53. The identified mutations consist of seven novel germ-line mutations, while three mutations have been reported previously. All the mutations are predicted to result in protein truncation. No mutations were identified in the remaining twenty-four candidate breast cancer genes. The present study provides the framework for the development of preventive and treatment strategies against breast cancers in Pakistani population.