Role of clonal lineage analysis via next-generation sequencing in identifying the origin of multiple cancers and guiding treatment options.

Multiple cancers occur in the same individual, such as hereditary breast and ovarian cancer (HBOC) syndrome and Lynch syndrome. Here, we report a patient with HBOC syndrome who developed four different cancer types (pancreatic cancer, right lung adenocarcinoma, prostate cancer, and left lung adenocarcinoma) within a relatively short period of 6.5 years. In HBOC syndrome, the lung adenocarcinoma is rare, and the tumors were initially suspected to be lung metastases from pancreatic cancer, respectively. The pathological analysis results in each of the three lesions were inconsistent. A whole-exome analysis was performed on all three tumors using next-generation sequencing (NGS). The results showed that many of the deletion mutations found in pancreatic cancer were not present in other lung tumors. Homologous recombination is required for the repair of deletion mutations, but this function is impaired in HBOC syndrome. Deletions occurring in the primary tumor are irreversible and should be inherited in metastatic lesions. Therefore, we hypothesized that these three cancers arose independently, that each lung tumor was a primary tumor rather than a metastasis of pancreatic cancer, and that their resection would be curative. This assumption was reasonable, as no new lesions were observed in a 10-year follow-up study since the onset of pancreatic cancer. Tracking genetic traits using NGS helps understand the origins and progression of malignant tumors.