eP337 - Survival in Stage IV Colorectal Cancer (CRC) at Diagnosis

Purpose/Background: The pathophysiology of colorectal cancer (CRC) differs between primary tumor location in the right colon, left colon and the rectum. Approximately 20-25% have metastatic disease at the time of diagnosis. There is paucity of data on prevalence of CRC metastasis patterns in US patients, as well as survival outcomes outside of single center data series. This study seeks to evaluate overall survival of metastatic CRC at presentation based on a doublet of disease primary site and metastatic site.Methods/Interventions: The National Cancer Database (NCDB) from 2016 to 2019 was queried for adult patients with pathologic diagnosis of stage IV CRC. Patients were excluded if they had multiple cancer diagnoses, unknown location of metastasis or primary tumor, or any pathology other than adenocarcinoma/signet cell or mucinous carcinoma. Patient demographic, tumor, treatment and outcome data was abstracted. The primary endpoint was overall survival (OS) indexed diagnosis and assessed using multivariable Cox regression.Results/Outcomes: We identified 41,661 patients with metastatic CRC at diagnosis representing 15.2% of patients who were diagnosed with CRC in this time interval. Most primary tumors arose from the left colon (39.8%) compared with the right colon (35.2%) and rectum (25.1%). Liver was the most common site of metastasis overall (46.2%). 43.9% of patients presented with M1b/1c disease, associated most with right colon primary. Lung metastases were more frequently associated with rectal primary versus right or left colon primary (10.1% vs 2.9% vs 3.8%). There was a high prevalence of KRAS mutation (48.7% of those tested) in metastatic disease, most common in right colon primary (58.2%). 40.4% of patients received surgery to the primary tumor, least often in rectal cancer patients. 18.0% received operative management of oligometastatic disease, more frequently in left colon primary than right colon or rectal primary (19.7% vs 17.5% vs 16.3%). Of patients receiving surgery to primary tumor 82.5% achieved negative resection margins and postoperative 30-day mortality was 4.2%. On multivariable analysis, age greater than 70, male sex and higher Charlson-Deyo Score were independently associated with worse OS whereas receipt of surgery to primary site and other site were independently associated with improved OS. The effect of metastasis location on OS was also found to significantly vary by primary location (p < 0.01). In general, survival decreased in the following order for each primary location: lung, other, liver and M1b/1c. However, the magnitude of OS differences varied by primary location with left being the most pronounced (Figure 1).Conclusion/

Discussion: Distribution of CRC metastases differ based on primary tumor location with lung metastasis most commonly arising from the rectum and M1b/1c disease most frequently arising from the right colon. Lung metastasis had improved OS compared to all other sites regardless of primary tumor location. This study highlights the need to consider primary tumor location in disease prognostication for patients with metastatic CRC, as well as feasibility of primary and metastatic resection.Figure 1. Kaplan-Meier Survival Curve for Metastatic Left Colon Primary based on Location of Metastasis. Figure 1. Kaplan-Meier Survival Curve for Metastatic Left Colon Primary based on Location of Metastasis.