Endoscopic ultrasound-guided tissue acquisition for assessment of resectability in pancreatobiliary cancer

Five-year survival rates for pancreatic cancer and biliary tract cancer are the first and second poorest, respectively, among all cancers in Japan. In clinical practice, computed tomography (CT) and other imaging modalities play a major role in determining treatment options, including surgery. Patients with pancreatic cancer are divided into three groups (i.e., resectable, borderline resectable, and unresectable). The degree of tumor invasion into the great vessels determines resectability. Therefore, diagnosis of perivascular soft-tissue cuffing (PSTC) is important when deciding whether a tumor is resectable.¹

Some pancreatobiliary cancers appear as PSTC on CT and magnetic resonance imaging (MRI). PSTC is thought to be caused by the complexity of lymphatic drainage,² a process called extravascular migratory metastasis (EVMM); however, differential diagnoses of PSTC include benign diseases such as retroperitoneal fibrosis and chronic pancreatitis. Diagnosis of EVMM among PSTCs on CT and MRI is difficult due to nonspecific, often diminutive, overlapping imaging features indicative of inflammation, as well as changes induced by therapy.

Endoscopic ultrasound (EUS) is superior to other modalities for detection of small lesions due to its superior spatial resolution.³ Moreover, preoperative EUS is better than CT for diagnosing vascular invasion by pancreatic cancer. In fact, a meta-analysis of nine studies comparing EUS with CT for assessment of vascular invasion by pancreatic cancer revealed that the diagnostic abilities of EUS and CT were a sensitivity of 69% and 48%, respectively, with an area under the curve (AUC) of 0.94 and 0.86, respectively.⁴ In addition, EUS-guided tissue acquisition (EUS-TA) enables a pathological diagnosis based on samples taken from lesions; this is especially important in cases where the differential diagnosis of PSTC is difficult, or when PSTC is detected by EUS alone. Moreover, accurate diagnosis based on EUS-TA is important for determining treatment strategies and avoiding unnecessary surgery. However, it should be noted that the accuracy of EUS-TA depends on the skill level of the endoscopist (i.e., expert vs. nonexpert).

Maehara et al. reported the sensitivity, specificity, and accuracy of EUS-TA for PSTC as 92.1%, 100%, and 92.5%, respectively, with a technical success rate of 98.1%.⁵ There are only two previous reports of EUS-TA for PSTC.^{6, 7} One of these found that the diagnostic yield of PSTC by EUS-guided fine-needle aspiration was 65%.⁷ Another recent report found that EUS-TA for PSTC had a sensitivity, specificity, and diagnostic accuracy of 81.1%, 100%, and 85.8%, respectively.⁶ Compared with previous reports,^{6, 7} the data presented in that report⁵ show that the diagnostic ability of EUS-TA for PSTC has improved markedly. Moreover, studies in a matched cohort revealed that the diagnostic ability of EUS-TA for PTSC (sensitivity 95.4%; specificity 100%; accuracy 95.7%) is the same as that for primary solid lesions (sensitivity 94.7%; specificity 100%; accuracy 95.7%).⁵ Remarkably, the accuracy was 95.4% for a lesion measuring ≥5 mm, 100% for a lesion measuring ≥10 mm, and 80% for a lesion measuring <5 mm.⁵ Therefore, the results show that for PSTCs of smaller size, the diagnostic performance is excellent. There are several possible reasons for this improvement. First, the authors utilized the right or left angulation control knobs on the endoscope to achieve an optimal angle for the longest possible puncture length; slight adjustments to the scope were made during the puncture to ensure that both the tip of the needle and the maximum length of the PSTC were captured in the same image. Second, advances in EUS equipment have improved the ability to delineate deeper areas. Third, improvements of puncture needle for the visibility/punctureability and appearance of the fine-needle biopsy needle make it possible to collect adequate specimens for pathological diagnosis.⁸

With respect to adverse events, EUS-TA for PSTC has the potential to cause hemorrhage, pseudoaneurysm, and thrombosis due to the proximity of blood vessels; however, because the risk of adverse events during EUS-TA for PSTC is the same (i.e., 1.9%) as that for primary lesions (2.4%),⁵ EUS-TA for PSTC can be performed safely. In clinical practice, a diagnosis of cancer can be obtained by EUS-TA for other lesions such as liver metastases or lymph nodes when a pathological diagnosis is difficult at the primary lesion. Also, EUS-TA for PSTC could be an alternative diagnostic option for cancer due to the high diagnostic ability and safety.

In this study, the accuracy of EUS-TA (92.4%) for a diagnosis of PSTC is greater than that of CT (75.4%).⁵ EUS-TA for PSTC has a higher diagnostic ability than CT. Thus, EUS-TA led to a change in the treatment strategy in nine cases (eight false-positives and one false-negative; 9/52, 17.3%).⁵ These results show that proactive EUS-TA overcomes the limitations of other imaging modalities, making it an important tool for improving treatment decision-making. In other words, EUS-TA can make a significant contribution to treatment decisions in clinical practice, including avoidance of unnecessary surgery and assessment of appropriate indications for surgery, which is the focus of the article.

Contrast-enhanced harmonic EUS (CH-EUS) also improves the diagnostic ability of EUS-TA for PSTC when compared with conventional EUS.⁹ The diagnostic accuracy of conventional EUS, CH-EUS, and contrast-enhanced CT for invasion into the portal vein is 72.7%, 93.2%, and 81.8%, respectively,⁹ making CH-EUS significantly superior to CT and conventional EUS for detecting vascular invasion. In addition, with respect to a primary tumor, combining CH-EUS with EUS-TA increased the sensitivity from 92.2% (EUS-TA alone) to 100% (combination).¹⁰ Further studies comparing EUS-TA performed with or without CH-EUS are needed to identify better diagnostic methods for PTSC.

The procedures reported in that study⁵ were performed by endoscopy experts working in a high-volume referral center. Future studies that determine whether similar safety and outcomes can be expected when EUS-TA for PSTC becomes widespread are awaited.

Author M.K. is a Deputy Editor-in-Chief of Digestive Endoscopy. The other author declares no conflict of interest for this article.

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