685 Background: Presence of lymphovascular invasion (LVI) is known to be a predictor of lymph node involvement in colon adenocarcinoma (CA). Lymph node involvement is associated with poorer prognosis necessitating adjuvant therapy. While some studies have suggested that LVI is a predictor of worse overall survival in early stage colon cancer, the significance of LVI on prognosis has not been tested in a comprehensive North American data set. Methods: Patients with stage II and III CA with LVI data available and those who received predefined standard of care treatment were identified from the National Cancer Data Base (NCDB) from 2011 to 2015. The relationship between LVI and overall survival was tested using Kaplan-Meier survival curves and Cox proportional hazards regression analysis after adjusting for relevant clinical and demographic variables. Hazard ratios and 95% confidence intervals are reported along with median overall survival (OS) where available. Results: The dataset included 93,070 patients with stage II and 66,701 patients with stage III CA. The proportion of patients with LVI was 13% in stage II and 47% in stage III CA. After adjusting for age, sex, gender, race, comorbidities, socioeconomic status, T, and N stage, LVI was associated with worse OS in stage II, HR 1.2 (1.15-1.25, p < 0.001), and in stage III, HR 1.25 (1.21-1.30, p < 0.001), CA. Median OS was 6.51 years with LVI versus. 6.85 years without LVI in stage II compared with 6.57 years with LVI versus not reached without LVI in stage III CA. Of the stage II patients with LVI, 20% received adjuvant chemotherapy (CT) and median OS was 6.91 years for those who did versus 6.07 years for those who did not receive CT. Conclusions: Our data suggest that LVI is an important predictor of OS in stage II and III CA. There is evidence that adjuvant chemotherapy improves OS in advanced CA but there remains uncertainty as to the benefit in stage II. Despite this uncertainty, guidelines suggest consideration of adjuvant CT in patients with high-risk stage II disease. Our data support the recommendation that LVI be considered a high-risk feature in stage II disease. Further studies are necessary to examine whether the type or duration of CT should differ for patients with CA and LVI.
PD-0461: Characterization of nodal metastases in prostate cancer patients at high risk for lymph node involvement