Why is involvement of arteries and veins important in the treatment of pancreatic cancer?
(Stage III, Locally Advanced and Borderline Resectable Pancreatic Cancers)
The location of the pancreas deep within the abdomen places it close to numerous large blood vessels that are necessary for life (see “Where is the pancreas?” post). As a result, cancers of the pancreas do not need to grow very large before invading these vessels and this poses a significant treatment problem. There are two main arteries in the area of the pancreas and these are called the celiac artery and the superior mesenteric artery. The celiac artery gives rise to the splenic artery and the hepatic artery and supplies blood to the liver, pancreas, spleen and stomach. The superior mesenteric artery gives rise to numerous branches that supply the small bowel, part of the colon and the pancreas. The venous system in this area is the portal vein and its tributaries. It drains blood from most of the gastrointestinal track back to the liver and ultimately to the heart through the hepatic veins. Pancreatic cancers that invade these major blood vessels are classified as Stage III which includes two subcategories – “border-line resectable” and “locally advanced, unresectable”.
Cancers that are found to completely surround one of the main arteries as determined by CT scan (“encasement”) are typically considered to not be operable (locally advanced, unresectable). An attempt at removal of such cancers has a very high probability of leaving a portion of the tumor behind (R2 resection) and thus the surgery will confer no survival benefit while potentially subjecting the person to debilitating side effects. Patients with locally advanced, unresectable pancreatic cancer will often undergo radiation and chemotherapy in hopes of shrinking the tumor away from the artery. Unfortunately, significant shrinkage of the tumor that converts it to removable occurs only 10% of the time. A tumor that grows next to one of the main arteries but does not surround it (“abutment”) is considered borderline resectable. In this case there is a good chance it can be removed without cutting though the tumor and, at worst, leaving only a few tumor cells behind (R1 resection). In most centers, including ours, patients with borderline resectable pancreatic cancer will receive radiation therapy prior to surgery in order to kill the cancer cells in the periphery of the tumor. This takes about 6 weeks and increases the likelihood of leaving no cancer behind at the margins (R0 resection). Unlike Stage III locally advanced pancreatic cancer, most patients with Stage III borderline resectable cancer will go on to have their tumor removed by surgery. The main exception to proceeding to surgery in borderline resectable patients is in the event the cancer grows further or develops distant metastases while receiving the chemotherapy and radiation therapy.
The assessment of whether or not a tumor is removable based on invasion of the main veins is very different than that of the arteries. Basically, any degree of involvement of the vein from abutment to encasement is considered to be borderline resectable as long as the tumor involves a portion of the vein that can be reconstructed once that section is removed. For example, if the tumor grows in the mid-portion of the vein (called the portal vein – superior mesenteric vein confluence), the tumor must be taken out with the vein attached and the two end of the vein can be reconnected to restore flow. If the same size tumor grows lower down on this vein (towards the feet), it will involve the portion of the vein that braches like numerous limbs of a tree. Removal of the vein in this area would leave the surgeon with one main “trunk” at the top and numerous “small braches” at the bottom. There would be no way to reconnect the ends. Thus for venous involvement, if it grows at a location in which the surgeon can technically remove the tumor and reconstruct the vein it is called Stage III borderline resectable. If removal and reconstruction is not possible it is called Stage III locally advanced. As described above for the arteries, patients with stage III cancers will most likely receive radiation therapy and most of those in the borderline resectable category will go on to surgery, while only 10% locally advanced will have significant tumor shrinkage.
There are numerous exceptions to this general algorithm based on feature that are unique to each individual patient. The complexity of the many treatment options underscores the need to be evaluated by an experienced team of specialists. We have found that this is best accomplished through a multidisciplinary clinic where patients are evaluated by all of the specialists in a single day. If you would like to learn more about this clinic please feel free to contact us at 410-933-PANC. We will be able to answer your questions and schedule a clinic appointment for you at your request.
Christopher Wolfgang, MD, PhD
Johns Hopkins Hospital