Investigation into the content of red material in EUS-guided pancreatic cancer biopsies

Background and Aims: The red material occupying the larger portion of the acquired sample in EUS fine-needle biopsy (FNB) is seldom investigated. We aimed to evaluate the composition of the red material. Methods: Patients with a solid pancreatic mass who received EUS FNB from September 2020 to June 2021 were enrolled. The white or yellowish content with apparent bulk (white material) and the rest of pasta-like red content (red material) were separated immediately after puncture. Needle passes proceeded until 2 specimens with >4 mm of white material were obtained. An extra needle pass was conducted for DNA collection. The DNA amount, Kirsten rat sarcoma virus (K-ras) mutation type, and mutation allele frequency were compared between the white and red material. Results: Forty patients were enrolled with 68 paired white and red materials. The diagnostic accuracy was slightly higher in the white material (92.5% vs 82.5%, P = .219). On the histology slides, the area of the tumor gland was comparable in both materials, but the total tissue area was larger in the red material (9.74 mm² and 10.74 mm² larger according to generalized linear model and generalized estimating equation, respectively; both, P < .001). The amount of DNA was significantly higher in the red material (2.99 [interquartile range, 1.59-7.29] μg vs .70 [interquartile range, .27-1.24] μg; P < .001). Common pancreatic adenocarcinoma K-ras mutation was identified at a rate of 85% for the white material and 95% for the red material. Regardless of whether red or white material was used, there was a high concordance of K-ras mutation types (34 of 40 [85%]) and a high correlation of mutation allele frequency (ρ = .66, P < .001). Conclusions: In EUS FNB, the red material contains a higher amount of tumor DNA and can be an alternative source for tumor DNA analysis.