MAY 20, 2016 6:38 AM PDT

Tumor Location Predicts Survival Odds in Colon Cancer

WRITTEN BY: Xuan Pham
Location, location, location! Researchers have found that colorectal patients whose tumor is located on the left side of the colon have better survival prognosis than patients whose tumor is located on the right side. The breaking discovery will be formally reported in June at the 2016 American Society of Clinical Oncology (ASCO) Annual Meeting.
 
Left vs. right really matters in colon cancer
In a large retrospective study of metastatic colorectal cancer, researchers identified data from 293 patients with right-sided primary tumors and 732 patients with left-sided primary tumors. The selected patients lacked mutations in the KRAS gene, which is known to influence response to certain drug therapies. The left side is defined as the descending colon, sigmoid colon, and rectum, whereas the right side includes the cecum and ascending colon.
 
Among the results, the key finding was that patients with left-sided primary tumors survived longer (33.3 months) than those with right-sided tumors (19.4 months). This trend persisted when the team factored in cetuximab and bevacizumab, two common therapies used to treat colorectal cancer. Cetuximab treatment prolonged survival to 36 months for left-sided tumors, while those with right-sided tumors lived 16.7 months. For bevacizumab, survival was 31.4 months for left-sided tumors, compared to 24.2 months for right-sided tumors.
 
Another interesting finding of the study is that drug effectiveness may be influenced by the location of the primary tumor. Right-sided tumors seem to respond better to bevacizumab than cetuximab, as reflected by longer patient survival (24.2 months and 16.7 months, respectively). By contrast, patients with left-sided tumors fared better with cetuximab than bevacizumab (36 months vs. 31.4 months). 
 
Cetuximab is a formidable defense against colorectal cancer, but recent studies have found that certain genetic mutations in KRAS influence whether this anticancer drug will be effective. In light of this, the team also conducted a separate analysis of 213 patients who carried KRAS mutations. Even in KRAS-mutated tumors, the team found that patients with left-sided tumor survived longer than patients with right-sided tumors.
 
“This is the largest study to date of tumor location in colorectal cancer, and it strongly suggests that this unexpected factor could answer some long-standing questions about why certain patients do better than others,” said ASCO President Julie Vose. “It is also an important reminder, in this exciting era of precision medicine, that genomics is not the only source of insight into how cancers should be studied and treated.”
 
Indeed, the primary location of the tumor in the colon appears to greatly influence the effectiveness of the treatment and overall patient survival. The biological mechanism driving this difference is currently being investigated.
 

Additional source: MNT, ASCO news release
About the Author
I am a human geneticist, passionate about telling stories to make science more engaging and approachable. Find more of my writing at the Hopkins BioMedical Odyssey blog and at TheGeneTwist.com.
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