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Differences in Prognoses for Patients With Right-Sided or Left-Sided Colorectal Cancer

Scott Kopetz, MD, PhD
Published Online:5:28 PM, Fri October 25, 2019

Scott Kopetz, MD, PhD, medical oncologist, Department of Gastrointestinal Medical Oncology, Division of Cancer Medicine, The University of Texas MD Anderson Cancer Center, explains how prognoses for patients with colorectal cancer (CRC) differ based on whether their cancer is left-sided or right-sided and discusses how knowledge of these differences have led to the development of more agents to treat both groups of patients.
 
Right-sided CRC results in a poor prognosis overall. Using standard therapies, these patients generally have lower progression-free survival (PFS) and shorter durations of response, says Kopetz. Right sidedness may also lead to recurrence after liver resection for metastases. Obtaining more knowledge about prognoses for right-sided disease has raised questions in the field related to how right-sided tumors should be treated and whether or not it has an impact on chemotherapy.
 
Studies have shown that targeted therapies don’t have the same activity in right-sided CRC as they do in left-sided CRC. Research around 2 EGFR-based therapies, cetuximab (Erbitux) and panitumumab (Vectibix), has shown that patients with tumor of the right side of the colon don’t respond as well to EGFR-targeted therapies as those with left-sided tumors, even if they do not have KRAS, NRAS, or BRAF mutations. This is what impacts PFS rates among patients with right-sided CRC treated with bevacizumab (Avastin)–based therapies. When compared with placebo, treatment with targeted therapies do not improve responses in right-sided tumors in later lines of treatment.
 
For left-sided CRC, patients do respond to EGFR-targeted therapies and show better responses compared with VEGF therapy.
 
Oncologists are currently trying to understand which patients with right-sided CRC should be treated with which targeted therapies to help improve outcomes overall.
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