Endoscopic ultrasound (EUS)–guided through-the-needle biopsies (TTNBs) of pancreatic cystic lesions are sufficient for accurate molecular analysis, which offers a superior alternative to cyst fluid obtained via fine-needle aspiration, based on a prospective study.
For highest diagnostic clarity, next-generation sequencing (NGS) of TTNBs can be paired with histology, lead author Charlotte Vestrup Rift, MD, PhD, of Copenhagen University Hospital, and colleagues reported.
“The diagnostic algorithm for the management of [pancreatic cystic lesions] includes endoscopic ultrasound examination with aspiration of cyst fluid for cytology,” the investigators wrote in Gastrointestinal Endoscopy. “However, the reported sensitivity of cytology is low [at 54%]. A new microforceps, introduced through a 19-gauge needle, has proven useful for procurement of [TTNBs] that represent both the epithelial and stromal component of the cyst wall. TTNBs have a high sensitivity of 86% for the diagnosis of mucinous cysts.”
Dr. Rift and colleagues evaluated the impact of introducing NGS to the diagnostic process. They noted that concomitant mutations in GNAS and KRAS are diagnostic for intraductal papillary mucinous neoplasms (IPMNs), while other mutations have been linked with progression to cancer.
The study involved 101 patients with pancreatic cystic lesions larger than 15 mm in diameter, mean age of 68 years, among whom 91 had residual TTNBs available after microscopic analysis. These samples underwent a 51-gene NGS panel that included the “most prevalent hot-spot mutations.” Diagnoses were sorted into four categories: neoplastic cyst, mucinous cyst, IPMN, or serous cystic neoplasm.
The primary endpoint was diagnostic yield, both for molecular analysis of TTNBs and for molecular analysis plus histopathology of TTNBs. Sensitivity and specificity of NGS were also determined using histopathology as the gold standard.
Relying on NGS alone, diagnostic yields were 44.5% and 27.7% for detecting a mucinous cyst and determining type of cyst, respectively. These yields rose to 73.3% and 70.3%, respectively, when NGS was used with microscopic evaluation. Continuing with this combined approach, sensitivity and specificity were 83.7% and 81.8%, respectively, for the diagnosis of a mucinous cyst. Sensitivity and specificity were higher still, at 87.2% and 84.6%, respectively, for identifying IPMNs.
The adverse-event rate was 9.9%, with a risk of postprocedure acute pancreatitis of 8.9 % and procedure-associated intracystic bleeding of 3%, according to the authors.
Limitations of the study include the relatively small sample size and the single-center design.
“TTNB-NGS is not sufficient as a stand-alone diagnostic tool as of yet but has a high diagnostic yield when combined with microscopic evaluation and subtyping by immunohistochemistry,” the investigators concluded. “The advantage of EUS-TTNB over EUS–[fine-needle aspiration] is the ability to perform detailed cyst subtyping and the high technical success rate of the procedure. ... However, the procedure comes with a risk of adverse events and thus should be offered to patients where the value of an exact diagnosis outweighs the risks.”
“Molecular subtyping is emerging as a useful clinical test for diagnosing pancreatic cysts,” said Margaret Geraldine Keane, MBBS, MSc, of Johns Hopkins Medicine, Baltimore, although she noted that NGS remains expensive and sporadically available, “which limits its clinical utility and incorporation into diagnostic algorithms for pancreatic cysts. In the future, as the cost of sequencing reduces, and availability improves, this may change.”
For now, Dr. Keane advised physicians to reserve molecular subtyping for cases in which “accurate cyst subtyping will change management ... or when other tests have not provided a clear diagnosis.”
She said the present study is valuable because better diagnostic tests are badly needed for patients with pancreatic cysts, considering the high rate of surgical overtreatment.
“Having more diagnostic tests, such as those described in this publication [to be used on their own or in combination] to decide which patients need surgery, is important,” Dr. Keane said who was not involved in the study.
Better diagnostic tests could also improve outcomes for patients with pancreatic cancer, she said, noting a 5-year survival rate of 10%.
“This outcome is in large part attributable to the late stage at which the majority of patients are diagnosed,” Dr. Keane said. “If patients can be diagnosed earlier, survival dramatically improves. Improvements in diagnostic tests for premalignant pancreatic cystic lesions are therefore vital.”
The study was supported by Rigshospitalets Research Foundation, The Novo Nordisk Foundation, The Danish Cancer Society, and others, although they did not have a role in conducting the study or preparing the manuscript. One investigator disclosed a relationship with MediGlobe. The other investigators reported no conflicts of interest. Dr. Keane disclosed no conflicts of interest.