Surprising new study shows colon cancer survival may be affected by tumor location

Colon cancer that starts on the left side of the body may be very different from that which starts on the right side. This is according to a new study from the University of California, San Francisco. Researchers who worked with more than 1,000 patients with colon cancer that had spread found that the length of survival for those with tumors on the left side averaged 33 months. However, those with tumors located on the right side survived only 19 months.

Different methods of treatment may be necessary depending on the origination site of the tumor, since those with left-sided cancer appear to have a better prognosis. Researchers think that this may be because polyps found on the right side are often flat, making them more difficult to spot during routine colonoscopies. This can allow them to turn into cancer.

Colon cancer deaths have been declining for several decades, but the condition is still one of the leading causes of cancer-related deaths in the U.S. Estimates from the American Cancer Society state that colon cancer is expected to result in 49,190 deaths in 2016.

Alan Venook, one of the study researchers, said that the study suggests that colon cancer may be a number of different diseases rather than just one. “Each side of the colon starts in a different place, which is why the cancers are biologically different. We don’t have just colon cancer, but varieties of colon cancer, and some have better prognosis than others.”

According to Venook, although previous research suggested that patient survival could be affected by tumor location, the new study indicated that the effects could be far greater than ever expected. The pattern continued in patients taking the chemotherapy drug cetuximab (Erbitux). Patients treated with cetuximab lived an average of only 17 months after beginning treatment with the drug if their tumor was on the right side. Those with left-side tumors survived an average of 36 months after beginning treatment.

Similar patterns were found with other drugs as well. Patients with right-side tumors lived just over 24 months after starting treatment with bevacizumab (Avastin). Survival time for left-side tumor patients on this drug was only about 31 months with treatment. Venook predicts that this information will lead to different treatment in the future, depending on which side the tumor is located on.