Circulating tumor DNA may correlate with tumor size changes following therapy.

Abstract

233 Background: Pancreatic cancer has significant mortality at five years, even in resectable disease. Recent effort has been dedicated to identify a more specific tumor marker for screening and assessing tumor response, in part because 10% of the population does not produce CA19-9. Detection and quantification of circulating tumor DNA (ctDNA) in the bloodstream is a novel concept for screening and treatment response assessment. This study examined possible correlations between ctDNA levels and various aspects of pancreatic cancer in a total of 17 patients receiving treatment at Banner MD Anderson Cancer Center. Methods: Present study is approved by our local IRB. Research was conducted according HIPPA regulation. Subjects on the present study were obtained from the list of patients participating in our ctDNA trial. A total of 17 subjects were identified from the list. Their ctDNA index levels were obtained from the sponsor (Chronyx) at baseline and following each cycle of the treatment. For each CT scan and each ctDNA study, they are considered the same time if they are obtained within 4 weeks of each other. The sizes of the primary tumor and the largest metastatic lesion were on a transverse image at the largest extent of the lesion. Data was analyzed with Spearman's correlation. Results: Baseline ctDNA levels did not correlate with patient demographic data (N = 17; gender, p = 0.63; age, p = 0.82), baseline size of primary mass on CT scan (N = 16; p = 0.85), baseline vessel involvement on CT Scan (N = 17; p = 0.58), presence of metastasis on CT scan (N = 17; p = 0.78), size of largest metastasis on CT scan (N = 17; p = 0.85), presence of peripancreatic lymph nodes on CT scan (N = 17; p = 0.45), or overall survival (N = 8; p = 0.6). However, there is a trend toward correlating the change in ctDNA and change in size on CT scan following treatment (N = 7; p = 0.12). Conclusions: ctDNA at baseline appears to be secreted independent of the primary tumor size, location, or presence of metastasis. However, changes in ctDNA does seem to correlate with changes in tumor size following treatment. Although our data was not statistically significant, this may be related to the low sample size. With larger sample size, it is expected that changes in ctDNA may prove to correlate with changes in tumor size.