By Robert Preidt
At issue are so-called left-sided and right-sided colon cancers, one oncologist who reviewed the findings explained.
"Left-sided cancers are located closer to the anus and located in the rectum, sigmoid colon and descending colon," said Dr. David Bernstein, chief of hepatology at Northwell Health in Manhasset, N.Y. "These cancers usually present with bleeding or partial obstruction [and] because of this presentation, patients tend to seek medical care earlier."
On the other hand, "right-sided lesions -- located in the first part of the colon, near the junction with the small intestine -- do not typically present with obstruction but tend to present with anemia and are more likely to be associated with metastatic disease, especially to the liver," Bernstein said.
Because they are often detected later in their progression, these right-sided colon tumors, "have a worse prognosis than left-sided colon cancers," he said.
That's what the new study found, as well. A team led by Dr. Fausto Petrelli, of the ASST Bergamo Ovest, in Treviglio, Italy, reviewed data from 66 studies. The studies involved a total of more than 1.4 million patients followed for a median of more than five years.
The result: colon cancer patients with left-sided tumors were nearly 20 percent less likely to die than those whose tumors occurred on the right side.
And there seemed to be more at play than simply later detection, the Italian team noted. The difference in survival between left- and right-sided colon cancer held even after the researchers factored out cancer stage at diagnosis, the study authors said.
Petrelli's group pointed to prior research that has shown that right and left colon cancers are genetically distinct, as well.
Based on the new findings, the study authors believe that "primary tumor locations should be carefully considered when deciding treatment intensity."
Another oncologist who reviewed the findings said that they have implications for patients deciding on which tool -- a sigmoidoscope or colonoscope -- to opt for in colon cancer screening.
"This report reaffirms the importance of choosing the appropriate screening tool for the prevention and detection of colon cancer," said Dr. Jules Garbus, a colorectal surgeon at Winthrop-University Hospital in Mineola, N.Y.
"Sigmoidoscopy provides a limited exam of the left side of the colon, from the anus directly up to the left upper abdomen," Garbus explained. "Colonoscopy, however, is a complete examination of the entire colon which extends past where the sigmoidoscopy reaches. The colonoscope crosses over to the right side of the abdomen and down to the right lower abdomen."
According to Garbus, "this study suggests that the location of the cancer may be an integral part of establishing prognosis and treatment, thus colonoscopy remains the gold standard in colon cancer screening."
The study was published Oct. 27 in the journal JAMA Oncology.