Baseline factors associated with acute progression of metastatic lesions after primary tumor resection in patients with unresectable colorectal cancer.

860 Background: In patients with unresectable colorectal cancer, primary tumor resection is expected not only local control but also prolongation of survival time. However, in some cases, metastatic tumors have been known to rapidly progress after primary tumor resection. We examined clinical factors associated with acute metastatic progress after primary tumor resection, and it might lead to worse survival. Methods: We retrospectively analyzed 183 patients who were newly diagnosed with unresectable colorectal cancer in our institution between April 2007 and April 2016. Among all patients, 83 patients received resection of primary tumor without the presence of symptoms. They were divided into progression and non-progression group according to metastatic progression that evaluated CT scan from four to six weeks after surgery. We analyzed clinicopathological factors related to acute progression after primary tumor resection using Cox proportional hazards. Results: After resection of the primary tumor, 25 patients were classified into progression group and 58 patients were classified into non-progression group. In progression group, the median percent change in the sum of the longest diameters of target lesions was 29.6% (10.0-191.7%), and 22 (88.0%) patients showed to have new lesions after resection of the primary tumor. Multivariate analysis revealed LDH (HR 4.44, 95%CI 1.15-18.5, p = 0.02), number of liver metastasis (HR 3.28, 95% CI 1.09-10.0, p = 0.03) and RAS status (HR 3.08, 95% CI 1.05-9.46, p = 0.03) were independent baseline factors associated with acute progression after resection of the primary tumor. The median overall survival (OS) was 12.3 and 27.8 months in progression and non-progression group, respectively. Conclusions: Serum LDH, number of liver metastasis, and RAS mutation were baseline factors associated with acute progression of metastatic tumors after resection of primary tumor in patients with unresectable colorectal cancer. These results indicated that the resection of the primary tumor in patients with these factors might be avoided when they have no clinical symptoms.