Clinical implementation of genomic medicine for patients with cancer is about to proceed in Japan. Cancer precision medicine using clinical sequencing is attracting a great deal of attention as a novel treatment strategy for patients with cancer. Above all, precision medicine for patients with pancreatic cancer is still developing and its clinical utility is unknown. However it is expected to be one of the most important therapeutic approaches to this disease.

At present, treatment-related information obtained by clinical sequencing of pancreatic cancer is limited. We can obtain valuable information to be applied in the clinical setting such as "Gene alterations associated with deficiencies in homologous recombination (BRCA1/2, ATM, BAP1, CHEK1/2, FANC, PALB2 etc)", "Genomic biomarkers associated with cancer immunotherapy (hypermutation, MLH1, MSH2, PMS2, EPCAM, POLE, POLD1, MSI-high, dMMR etc)", "KRAS wild-type pancreatic cancer", and "The number of mutated KRAS, TP53, CDKN2A, SMAD4". Clinical sequencing of pancreatic cancer is limited by several disease-specific difficulties in genome sequencing. However clinical application of precision medicine for the disease is feasible and promising in clinical practice.

Advances in next-generation sequencing (NGS) technology have revealed the landscape of genomic alterations in patients with pancreatic cancer. NGS-based genomic profiling forms the basis of precision cancer medicine through the identification of potentially actionable mutations. However, few studies have addressed genomic analysis in patients with unresectable pancreatic cancer partly because of the difficulty in acquiring a biopsy sample suitable for genomic analysis due to abundant fibrosis in cancer tissue. In this article, we provide an overview of genomic alterations in patients with pancreatic cancer and discuss the current status and future issues regarding genomic analysis using EUS-FNA samples.

Surveillance of IPMN is conducted by imaging studies stratified by cyst size. Although this surveillance is mainly for diagnosing PDC derived from IPMN, it is not sufficient for diagnosing PDC concomitant with IPMN. Endoscopic ultrasonography is reported to facilitate diagnosis of PDC concomitant with high frequency during follow-up of IPMN. Ideally, less painful examinations should be combined with conventional studies for surveillance of IPMN. One possibility is to perform genetic analysis using body fluids such as blood, urine, pancreatic and duodenal secretions. From an analysis of resected tissue by next-generation sequencing, the TP53 mutation was identified as a marker for PDC derived from IPMN and PDC concomitant with IPMN, and multiple KRAS mutations were identified as candidate markers for PDC concomitant with IPMN. We detected these markers from an analysis of pancreatic exocrine secretions.

Detection of circulating tumor DNA released from dying/dead tumor cells into the blood has drawn attention as a potential biomarker for cancer. In this study, we developed a system to detect circulating tumor DNA from pancreatic cancer using next-generation sequencing. DNA regions of 8 genes including KRAS, TP53, SMAD4 and CDKN2A genes, where somatic mutations are known to be frequently observed in patients with pancreatic cancer, were amplified and sequenced. Application of the non-overlapping integrated read sequencing system, a high-fidelity target sequencing method using the molecular barcode, and the bioinformatics CV78 filter system to efficiently exclude non-tumor-specific variant DNA, resulted in more accurate detection of pancreatic cancer-related variant DNA in the blood. Using this system, pancreatic cancer-related variant DNA was detected in approximately 35% of patients with pancreatic cancer. The disease tended to be more advanced in patients having pancreatic cancer-related variant DNA than in those without it. We plan to validate the utility of this system for identifying circulating tumor DNA from pancreatic cancer in future clinical trials.

BRCA1, BRCA2, and PALB2 are BRCA-pathway genes whose products are associated with homologous recombination repair of double strand breaks of DNA. Germline mutations of BRCA-pathway genes are known to elevate the risk for development of pancreatic cancer. However, BRCA-pathway gene mutations in tumors are associated with susceptibility to cisplatin and the poly ADP ribose inhibitor, which may have a dramatic therapeutic effect. We investigated BRCA-pathway gene mutations in sporadic pancreatic ductal adenocarcinomas (PDACs), familial PDACs, and pancreatic acinar cell carcinomas, and found that 2.4%, 9.3%, and 43% of sporadic PDACs, familial PDACs, and acinar cell carcinomas, respectively, harbored pathogenic mutations, i.e., frameshifts or nonsense mutations of BRCA-pathway genes. Patients with sporadic PDACs with pathogenic mutations and variants of unknown significance had longer survival than those with PDACs with benign variants or no mutations. Complete remission of multiple liver metastases from a pancreatic acinar cell carcinoma with a BRCA2 mutation by treatment with cisplatin was observed. Pancreatic cancers with BRCA-pathway gene mutations are likely to respond well to certain drugs, hence identifying patients with such tumors is particularly important in the era of genomic medicine.

A 72 year-old man, with a history of a pancreatic pseudocyst with previous hemorrhage, underwent endoscopic mucosal resection of descending colon polyps. He developed a persistent high fever in the evening after resection. Two days after resection, he presented with fever and fatigue. Blood tests showed an elevated white blood cell count, and contrast-enhanced computed tomography scan showed increased pancreatic cysts. He was admitted for treatment of the pancreatic pseudocyst. A high-level inflammatory reaction persisted despite non-operative treatment, and a fistula to the digestive tract was suspected on the basis of CT imaging. A colonoscopy was performed, and a 5mm opening was found in the descending colon. Injection of contrast medium confirmed a fistula to the pancreatic cyst. The pancreatic pseudocyst-descending colon fistula was closed by endoscopic clip placement. There are previous reports of rupture in the abdominal cavity with penetration into the gastrointestinal tract as a complication of a pancreatic pseudocyst, This was a much rarer case of pancreatic pseudocysts-gastrointestinal fistula caused by therapeutic colonoscopy.

【Case Presentation】A 70 year old male with back pain and fever was diagnosed with acute pancreatitis and a pseudoaneurysm of the splenic artery at another hospital. During the treatment of pancreatitis, a mass was found on CT scan in the pancreas and he was referred to our hospital. CT scan showed a hypo-dense 20mm tumor, a recurrent pseudoaneurysm, and fluid suspected to be walled-off necrosis in the pancreatic tail. After coil embolization of the pseudoaneurysm, distal pancreatectomy with splenectomy was performed. The preoperative diagnosis was cancer in the tail of the pancreas based on FDG uptake on PET scan and a mass of increasing size, The postoperative course was uneventful, and he was discharged from the hospital on postoperative day 14. Pathological findings showed a Stage IIA (7th edition of the classification of the Japan Pancreas Society) moderately differentiated tubular adenocarcinoma. Two months later postoperatively, local recurrence and liver metastases were detected on CT scan. The recurrent tumor was resistant to chemotherapy and he died from pancreatic cancer seven months after operation. Although pancreatic cancer associated with acute pancreatitis is rare, aggressive evaluation and early treatment are recommended to prevent a poor outcome, as in this patient.