Endoscopic ultrasound (EUS) was originally developed to detect pancreatic tumors in the earliest, most treatable stages. Today, EUS remains the primary method for evaluating and staging pancreatic cancer and has emerged as a valuable tool for screening people at high risk of the disease. In the past few years, however, the role of EUS has expanded well beyond its use in diagnostic imaging.
One of the most important and widely used new applications is EUS-guided fine-needle aspiration cytology (EUS-FNA). EUS-guided biopsies allow minimally invasive sampling of tissue from tumors and lymph nodes not easily accessible by other methods.
According to Michael B. Wallace, M.D., chair of the division of gastroenterology and hepatology at Mayo Clinic in Jacksonville, Florida, EUS-FNA has not only significantly changed the staging and management of gastrointestinal tumors but also the mediastinal staging of lung cancer.
"Although EUS is thought of as a tool for assessing cancers of the digestive system, it is now arguably one of the preferred methods for the preoperative assessment of nonsmall cell lung cancer, replacing invasive procedures such as mediastinoscopy and thoracoscopy," he says.
A definitive trial performed by the Florida group showed that a combination of EUS-FNA and endobronchial ultrasound-guided fine-needle aspiration (EBUS-FNA) can provide nearly complete staging of the mediastum and is significantly better than previously available methods.
In the mid-1990s, EUS-guided biopsies, coupled with advances in molecular biology, led to the development of biomarker-based diagnoses. Since then, biomarkers have played an integral role in distinguishing premalignant or malignant pancreatic cysts from benign ones — historically a problematic and unreliable process. Now, analysis of cyst fluid proteins collected by EUS-FNA, along with cytology and imaging tests, may help determine which cysts require surgical intervention.
Molecular testing for tumor markers and genetic mutations can also help guide therapy. "Some genetic biomarkers are predictive of how certain people will respond to particular therapies," Dr. Wallace says. "Our group has done a great deal of work in this area, and it has been very helpful for a subset of patients."
More recently, EUS has evolved from an increasingly sophisticated diagnostic tool into a promising therapeutic one. So far, the most widely available and successful intervention has been pancreatic pseudocyst drainage. EUS guidance allows cysts to be imaged and drained without the risks and potential complications of other methods of cyst puncture.
EUS has also been used to drain abscesses in the abdomen, chest and pelvis, and EUS-guided cholangiopancreatography is an option when ERCP fails or isn't possible. Dr. Wallace notes that within the past few months, a number of new systems have become available that increase the technical feasibility and convenience of these and other therapeutic procedures, including gallbladder drainage and, potentially, nonsurgical removal of gallstones under EUS guidance.
Several studies have examined EUS-guided ablation of pancreatic cystic neoplasms using ethanol or chemotherapeutic agents such as paclitaxel. Study results show that this approach — which avoids surgery and the expense, inconvenience and potential risks of longterm monitoring — is moderately effective and durable, but longer follow-up is needed.
Dr. Wallace points out that EUS is also a safe and effective method for placing fiducial markers in people undergoing radiation therapy for pancreas cancer. "Fiducials are small metallic seeds typically made with gold coils. Placed inside a tumor, they reduce organ motion errors, allowing more precise targeting of tumors and minimizing harm to healthy tissue."
EUS-guided fiducial placement is used at Mayo Clinic in Florida for both standard radiotherapy and proton therapy, and is applicable to all patients with pancreas cancer. Radioactive seeds can also be implanted in tumors under EUS-guidance.
Dr. Wallace believes the original intent behind endoscopic ultrasound — the detection of early pancreatic cancer — has been fulfilled. "EUS has emerged as the most promising screening test for pancreatic cancer, so after 30 years, that is coming to fruition. What lies ahead is even more exciting."