Bile Cell Block‐Derived DNA for Next‐Generation Sequencing in Cholangiocarcinoma: A Comparison With Surgical Specimens

OBJECTIVES: A sufficient amount of cancer tissue for next-generation sequencing (NGS) is difficult to obtain from patients with unresectable cholangiocarcinoma. We evaluated whether bile cell block (CB) samples provide a DNA source of sufficient quantity and quality for NGS compared with surgical specimens. METHODS: NGS results of paired bile CB and surgical specimens from 14 patients were compared. RESULTS: Median number of malignant cells on one glass slide of CB specimen was 50. Although median DNA concentration and amount of extracted DNA were significantly lower in the CB than those in the surgical specimens, NGS success rate did not differ significantly (CB, 64%; surgical specimen, 86%). In a pair-wise comparison of eight patients with successful NGS of both bile CB and surgical specimens, median gene matching rate was 99%, and median coverage rate of surgical genes based on CB genes was 100%. The presence of ≥ 30 malignant cells on a single slide was identified as a practical indicator of successful NGS of CB using receiver operating characteristic curve, and this threshold increased the NGS success rate to 80%. CONCLUSIONS: As bile CB is easy to prepare in general hospitals, bile cell-based NGS may help address the difficulty of obtaining surgical NGS samples for cholangiocarcinoma.