Abstract 3750: Conversion surgery in unresectable advanced gastric cancer and cancer dormancy as a prognostic marker

Background: While additional gastrectomy has not shown superiority compared to conventional systemic therapy in unresectable gastric cancer in REGATTA trial, there have been several subsequent attempts to find a role for conversion surgery with a curative intent in selected patients. The aim of this study was to analyze the conversion surgery data and to see if there was a role of cancer dormancy markers to select patients for conversion surgery. Patients and Methods: From the pathology database at Seoul National University Bundang Hospital, we identified 49 patients treated with chemotherapy followed by gastrectomy in initially unresectable gastric cancer from January 2006 to August 2016. Of these, 26 patients were analyzed to explore the role of conversion surgery with a curative intent. As cancer dormancy markers, NR2F1, nanog, mig6, and pERK were evaluated using immunohistochemistry staining. Results: Twenty-six (53%) from a total of forty-nine patients received conversion surgery. The median age was 58 years (range, 39-78) and the duration of prior chemotherapy before conversion surgery was 5.1 months (range, 3.1-13.9). Category 2 with para-aortic lymph node involvement was the most prevalent disease status (57.5%). At the time of conversion surgery, complete response, partial response, and stable disease status had been established with chemotherapy in 2, 15, and 3 patients, respectively. Of these, R0 resection was accomplished in twenty-two (85%) patients. Median overall survival (OS) in all patients that underwent conversion surgery, defined as the time from initiation of chemotherapy to death by any cause, was 36.1 months (95% CI, 29.6-51.4). In patients that underwent R0 resection, disease free survival (DFS) from conversion surgery and OS from initial chemotherapy was 15.1 months (95% CI, 13.9-43.8) and 37.8 months (95% CI, 31.7-57.1), respectively. Patients with a shorter duration of prior chemotherapy were associated with both longer OS and DFS from conversion surgery (p < 0.001, both). Less advanced pathologic stage at the time of conversion surgery was also associated with longer OS from conversion surgery (p=0.045). Regarding cancer dormancy markers from initial biopsy specimens, stronger expression (moderate to strong) of NR2F1, nanog, and mig6 showed a tendency for longer DFS after conversion surgery (p=0.018, p=0.834, p=0.344, respectively) and also longer OS after conversion surgery (p=0.027, p=0.225, p=0.359, respectively). Conclusion: