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Pancreatectomy Predicts Improved Survival for Pancreatic Adenocarcinoma: Results of an Instrumental Variable Analysis

McDowell, Bradley D. PhD*; Chapman, Cole G. BS; Smith, Brian J. PhD; Button, Anna M. MS; Chrischilles, Elizabeth A. PhD§; Mezhir, James J. MD

doi: 10.1097/SLA.0000000000000796
Original Articles

Background and Objective: Pancreatic resection is the standard treatment option for patients with stage I/II pancreatic ductal adenocarcinoma (PDA), yet many studies demonstrate low rates of resection. The objective of this study was to evaluate whether increasing resection rates would result in an increase in average survival in patients with stage I/II PDA.

Methods: SEER (Surveillance, Epidemiology, and End Results) data were analyzed for patients with stage I/II pancreatic head cancers treated from 2004 to 2009. Pancreatectomy rates were examined within Health Service Areas (HSAs) across 18 SEER regions. An instrumental variable analysis was performed, using HSA rates as an instrument, to determine the impact of increasing resection rates on survival.

Results: Pancreatectomy was performed in 4322 of 8323 patients evaluated with stage I/II PDA (overall resection rate = 51.9%). The resection rate across HSAs ranged from an average of 38.6% (lowest quintile) to 67.3% (highest quintile). Median survival was improved in HSAs with higher resection rates. Instrumental variable analysis revealed that, for patients whose treatment choices were influenced by rates of resection in their geographic region, pancreatectomy was associated with a statistically significant increase in overall survival.

Conclusions: When controlling for confounders using instrumental variable analysis, pancreatectomy is associated with a statistically significant increase in survival for patients with resectable PDA. On the basis of these results, if resection rates were to increase in select patients, then average survival would also be expected to increase. It is important that this information be provided to physicians and patients so that they can properly weigh the risks and advantages of pancreatectomy as treatment of PDA.

When controlling for confounders using instrumental variable analysis, pancreatectomy is associated with a statistically significant increase in survival for patients with resectable pancreatic ductal adenocarcinoma. Therefore, if resection rates were to increase in select patients, then average survival would also be expected to increase. Further evaluation of how to remove barriers to pancreatectomy is needed.

*Holden Comprehensive Cancer Center

Departments of Health Services Research

Biostatistics

§Epidemiology

Surgery, The University of Iowa College of Public Health and University of Iowa Hospitals and Clinics, Iowa City, IA.

Reprints: James J. Mezhir, MD, Division of Surgical Oncology and Endocrine Surgery, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, 4642 JCP, Iowa City, IA 52242. E-mail: james-mezhir@uiowa.edu.

Presented in part at the Society of Surgical Oncology Annual Symposium, March 2013, and the American Society of Clinical Oncology Gastrointestinal Symposium, February 2013.

Disclosure: Supported in part by the Holden Comprehensive Cancer Center Population Research Core and Biostatistics Core (P30 CA086862). The authors have no financial disclosures or conflicts of interest.

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