Right (R) or left (L) primary site of colorectal cancer and outcomes for metastatic colorectal cancer (mCRC): Results from the south Australian registry of mCRC.

596 Background: Previous reports have described differences in biology and outcome based on whether the primary is R or L sided. Possible differences in response to biological agents have also been reported based on side of primary lesion (SY Brule et al., JCO31, 2013 (supp #3528). Methods: We explored the SA mCRC registry to assess if there were any differences in patient characteristics, treatment received and outcomes based on whether the primary was R (caecum to transverse colon) or L (splenic flexure to rectum) sided (JA Bufill, Ann Int Med. 113, 1990, 779-788). KM was used for survival outcomes and Cox proportional hazards regression modeling was used to assess defined prognostic markers. Results: 2,877 patients were analysed. 33% had R sided primary. Major differences between R and L respectively are as follows; Female 51.3% vs. 37.9% (p = <0.0001), Med age 75.8 yrs vs. 70.5yrs (p = <0.0001), poorly differentiated pathology 34.3% vs. 20.8% (p = <0.0001), KRAS mutation 48% vs. 37% (p = 0.023), and l...