Systemic treatment and primary tumor location in patients with metastatic colorectal cancer

Purpose: Tumor location (right-sided vs. left-sided) is known to exert a significant influence on the prognosis of primary colorectal cancer (CRC). Given the genetic continuity between primary and metastatic lesions, we aimed to summarize the existing literature on the prognostic implications of primary tumor site as well as to examine the response to chemotherapy by primary tumor location in patients with metastatic CRC (mCRC). Methods: A structured review of the literature was performed between 6/1/2016-7/1/2016 using the Pubmed database. Original research articles published between 1/1/2000-07/01/2016 were considered eligible. The primary endpoints were overall survival (OS)/ progression free survival (PFS) and response to systemic treatment in patients with mCRC. Results: Eleven studies were included. Tumor site was a strong independent predictor of worse OS/PFS in 9 studies, with right-sided tumors having worse prognosis in all cases. Furthermore, 6 studies demonstrated an inferior response to systemic treatment or worse prognosis following the administration of specific regimens among patients with right-sided cancers. As such, there is significant evidence that right-sided lesions are associated with poor outcomes and resistance to systemic treatment. Conclusion: Consequently, primary tumor location should be a consideration, when the administration of systemic therapy is contemplated in mCRC.