NEW YORK, Apr 18 (Reuters Health) - Specific genetic changes that occur in colon tumors can help doctors predict which patients will benefit the most from chemotherapy after surgery, new study findings suggest.

While chemotherapy is often given to these patients in an attempt to wipe out any cancerous cells that surgery failed to remove, it does not benefit all patients.

"Identifying tumors that are not going to be sensitive to chemotherapy...will allow patients to not waste their time going through courses of chemotherapy," which can have serious and debilitating side effects, Dr. Stanley R. Hamilton of University of Texas MD Anderson Cancer Center in Houston, and the study's senior author, told Reuters Health.

Hamilton and his colleagues analyzed tumor tissue from 460 patients with colon cancer who were treated with standard chemotherapy drugs. Their findings appear in the April 19th issue of The New England Journal of Medicine.

Patients who had lost a chunk of chromosome 18 were less likely to survive five years after surgery compared with other patients. Those with two other markers--microsatellite instability and a mutation in a certain gene--were more likely to survive.

Microsatellite instability (MSI) occurs when a defective DNA repair mechanism leads to abnormalities in a tumor cell's genetic code.

But further research is needed to investigate whether these molecular markers apply to chemotherapy regimens based on newer drugs, such as irinotecan and oxaliplatin, Hamilton said.

Loss of material from chromosome 18 occurred in 49% of tumors, high levels of MSI were found in 21% of tumors, and the gene mutation occurred in 61% of tumors.

"Markers that reliably predict survival are needed," the study authors write. "Our study is a first step toward the goal of individualized cancer treatment based on the molecular characteristics of the tumor."

　　From ReutersHealth