Early molecular assessment to predict prognosis in patients who respond to chemotherapy on initial imaging in pancreatic cancer.

Abstract

683 Background: It is helpful to predict early the response to anticancer drugs in non-resectable solid tumors. The purpose of this study is to evaluate whether circulating tumor DNA (ctDNA) helps predict prognosis in patients with non-resectable pancreatic cancer who have received first-line FFX or GnP therapy and have responded to treatment (CR, PR, SD groups) on initial imaging. Methods: A total of 61 patients with non-resectable pancreatic cancer treated with FFX (N=22) and GnP (N=39) as first-line therapy were included in the study. Before and after chemotherapy treatment (median 42 days, after two courses), KRAS-mutated ctDNA was measured using droplet digital PCR with CA19-9. We defined the Responder group as those with CR, PR, or SD other than PD on initial imaging and the molecular assessment as the change in KRAS-mutated ctDNA before and after treatment. (1) No appearance of KRAS-mutated ctDNA before and after treatment was defined as molecular negative (mNT); (2) disappearance of KRAS-mutated ctDNA or decrease in copy number after treatment was defined as molecular response (mR); (3) new appearance of KRAS-mutated ctDNA or increase in copy number after treatment was defined as molecular progressive disease (mPD). We investigated whether the increase or decrease of CA19-9 before and after treatment (Increase group, decrease group) and the molecular assessment were useful as prognostic factors in the Responder group. Results: Male: female = twenty-nine: thirty-two. There were fourteen patients in the locally advanced group and forty-seven patients in the distant metastatic group, both of whom were considered non-resectable. Thirty-eight patients received any second-line treatment. The prognosis of fourteen patients with PD on initial imaging was significantly worse than that of the Responder group (N=47) (Responder: PD=18.4: 9.2 months, p=0.000108). The molecular assessment in the responder group showed 30 patients in mNT group, 10 patients in mR group, and 7 patients in mPD group. The MST was 21.7, 13.2, and 13.2 months. In univariate analysis, increased CA19-9 (Increase group) and mPD were associated with worse prognosis (Increase: Decrease=13.6: 18.4 months, p=0.0487), (mPD: mNT+mR=13.2: 21.7 months, p=0.0194) and the only independent prognostic factor in multivariate analysis was mPD (Hazard ratio=3.005, p=0.0361). Conclusions: The prognosis of patients with molecular negative or molecular response after chemotherapy is relatively good (MST; 21.7 months), and efforts should be made to continue GnP and FFX. In contrast, the prognosis of patients with molecular progressive disease in the responder group is worse. Therefore, strict follow-up and change of anticancer drugs, including palliation, should be considered.