Postoperative adjuvant therapy for pancreatic cancer.

Abstract

The majority of patients diagnosed with pancreatic cancer present at an advanced stage, and only a small percentage are considered technically resectable at diagnosis. The overall prognosis for the majority is dismal, with a median survival in untreated cases of only 24 weeks. Even in resected patients the overall 5-year survival rate is generally only 5% to 10%; however, some reports indicate higher 5-year survival rates in patients treated with surgery who are pathologically staged with no lymph node involvement. Even when macroscopically complete resection is achieved, local recurrence (LR) rates are unacceptably high (30% to 70%), which is usually attributed to the difficulty of obtaining microscopically free surgical margins. Microscopic clearance is difficult to achieve because these tumors frequently extend into the peripancreatic tissues (e.g., retropancreatic fat), abut or invade the adjacent large vessels (the portal vein and superior mesenteric artery), and have a propensity to invade the lymphovascular and perineural space. Other common sites of failure after attempted curative resection include metastasis to the liver and the peritoneal cavity. Patients who present with pancreatic cancer, and for whom curative surgery is deemed possible, are thus potential candidates for adjuvant therapy because of the high local failure rate following resection alone. The radiotherapy dose that can be achieved in the postoperative setting for pancreatic cancer is limited because of the proximity of critical structures (e.g., the kidney, liver, small intestines, stomach, and spinal cord). Newer techniques such as conformal radiotherapy and intensity-modulated radiotherapy have the advantage of being able (theoretically) to precisely localize the dose to the target volume while reducing the dose to critical structures. These techniques may potentially enable the tumorcidal dose to be increased; however, they are only now becoming widespread. Systemic radiation-sensitizing chemotherapy is also a promising approach to take advantage of additive or synergistic effects with radiation locally, and for the sterilization of systemic disease. This concept of concomitant chemotherapy with radiotherapy, or chemoradiotherapy, has proved effective in a number of sites, including the anal canal, rectum, lung, and pancreas. The recent trials reviewed here varied considerably in terms of the total dose and technique used, and the choice of radiation sensitizing treatment.