Sidedness in metastatic colorectal carcinoma: Which are the factors which influence the prognosis?

497 Background: Recent reports demonstrate prognostic and predictive impacts of the location of the primary tumor in metastatic colorectal cancer (mCRC). Our retrospective analysis aimed to determine the influence of primary site on metastatic distribution and disease evolution. Methods: From our database all patients (pts) with mCRC (except transverse carcinoma) treated from 1/12/2007 to 1/12/2016 in our institution were collected. Univariate and multivariate analyses were performed to identify predictors of overall survival (OS). Results: A total of 284 pts with available data were analyzed: 83 with Right-sided Colon Cancer (RCC) (29%), 123 with Left-sided Colon Cancer (LCC) (43%) and 78pts with Rectal Cancer (RC) (28%). Hepatic, lung, lymph nodes and peritoneal metastases were respectively found in 63%, 36%, 23% and 20% of the population. The incidence or number of liver metastases were not influenced by sidedness (p = 0.06), LCC presented more bilobar involvement compared to RCC and RC (p = 0.017). Peritoneal carcinomatosis was significantly correlated to colon cancer (p = 0.002), whereas lung metastases were more common in RC (p < 0.001). Patients with RCC more often presented distal lymph node involvement (p = 0.008). RAS mutation status was known for 241pts (80%), of those 110 (37%) were RAS mutated with no significant differences between RCC, LCC and RC (p = 0.4), BRAF mutation (p = 0.007) was more common in RCC. On a multivariable analysis, primary tumor resection (PTR) and complete response after first line therapy were associated with a better OS but only a trend was observed for LCC and RC. Lung, lymph and peritoneal metastasis were associated with worse OS (Table). Conclusions: These results suggests that mCRC had different clinical presentation at diagnosis, the association with molecular features may explain the independent prognostic factor for OS of the sidedness. [Table: see text]