I. A. Naqvi1, R. Gunaratne1, D. Pisetsky2, R. R. White1 1Duke University Medical Center,Surgery,Durham, NC, USA 2Duke University Medical Center,Medicine,Durham, NC, USA
Introduction: Pancreatic cancer (PC) is the deadliest of the major cancers, and response rates to standard therapies are low. DNA is released by tumors, and circulating extracellular DNA (exDNA) and nucleosomes (short segments of DNA wrapped around histones) have been evaluated as markers of disease burden for prognosis and response to therapy. We hypothesized that exDNA and nucleosome (NUC) levels would decrease in patients undergoing neoadjuvant chemoradiation (neoCRT) for localized PC.
Methods: Blood was collected from 1) patients with radiographically localized PC (N=8) before and 4-6 weeks after neoCRT, 2) patients with advanced disease (N=3) and 3) normal volunteers (N=5) in order to create a spectrum of data for disease burden. ExDNA and NUC were isolated from serum samples and quantified using a fluorescent DNA-specific stain (Picogreen) and ELISA, respectively.
Results: There was a strong correlation between exDNA and NUC levels, and therefore only exDNA levels are shown. Healthy individuals had the lowest levels of exDNA while patients with advanced disease had the highest levels (Figure 1). Overall, exDNA levels increased in patients who underwent neoCRT to levels similar to those of patients with advanced disease, regardless of whether they had radiographic partial response (PR, N=4), stable disease (SD, N=4), or progressive disease (PD, N=2) on restaging (Figure 2) nor whether they were subsequently able to undergo resection (not shown).
Conclusion: Contrary to our hypothesis, exDNA levels increased in response to neoCRT. These data suggest that exDNA is not simply a marker of disease burden. We postulate that exDNA is released by tumor cells in response to therapy and also by host immune cells in response to the tumor. In order to put this into a broader context, we are expanding our dataset to include more patients and time points, including pre- and post-resection. We are evaluating other specific forms of exDNA as well as DNA-associated proteins as markers of cell death that may be more useful for monitoring response to therapy.
