Pancreatic Cancer: Guiding PDT with Ultrasound
For most people diagnosed with pancreatic cancer, the prognosis is dire. That’s because the disease has almost alway advanced to the metastatic stage. Indeed, most patients already have extensive metastases, primarily in the liver, colon, and lymphatic system. At the same time, the deep abdominal location of the pancreas makes it quite difficult to surgically remove a pancreatic tumor in its entirety.
One of the tools that surgeons have developed in recent years to better locate and remove pancreatic tumors is called endoscopic ultrasound (EUS). As the name implies, this procedure has two parts: (1) endoscopy, which entails inserting a long flexible tube, or endoscope, via the mouth or rectum to visualize the digestive tract; and (2) ultrasound, which uses high-frequency sound waves to generate images of the pancreas and other structures inside the body. With EUS, one can obtain high-quality ultrasound images of the pancreas and surrounding structures.
EUS-guided removal of pancreatic tumors is emerging as a promising way to treat this deadly cancer. But in many cases, as mentioned above, surgery is not an option, because the cancer is too large or extensive within the pancreas. In such cases, the light-based approach called photodynamic therapy, or PDT, may be of great value.
PDT utilizes a photosensitizer together with light emitted via small optic fibers to remove the tumor. After being administered, the photosensitizer accumulates in malignant tissue but not normal tissue. Light passing through the optic fibers activates the photosensitizer, resulting in the formation of highly reactive oxygen molecules that damage the tumor while also triggering anti-cancer immune mechanisms.
EUS-Guided PDT: What the Research Shows
Early studies of PDT for pancreatic cancer focused on animal models for the disease. A laboratory study at Massachusetts General Hospital in Boston (USA) demonstrated the safety and feasibility of using EUS-guided PDT in the porcine pancreas, an approach that led to complete necrosis, i.e., 100% breakdown of the tumor. A similar study at the same hospital showed that PDT caused the destruction of cancer in the pancreatic tail without causing any complications.
Human research on PDT for pancreatic cancer is limited but has been shown to be safe and well tolerated. In one small retrospective study of this method, survival was comparable to that of conventionally treated patients, as reported in the 2014 British Journal of Cancer. Although the study was not designed rigorously enough to assess survival, it did suggest that PDT could, in some cases, shrink the cancer enough to enable successful surgery.
Of course, this is just one small study, and thus the value of EUS-guided PDT has yet to be adequately tested in humans. Nevertheless, the procedure appears to be safe and offers a less invasive way to remove pancreatic tumors, especially those tumors that cannot be directly accessed and surgically removed through EUS. It follows that the photodynamic treatment of pancreatic cancer merits serious research attention in the years ahead.
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