Genetic mutations can show which breast cancer patients will be helped by a certain type of chemotherapy, U.S. researchers reported on Tuesday.

They found patients with two versions of SOD2 fared worse when taking the chemotherapy drug cyclophosphamide than other patients. It might be useful to test patients for this gene before giving them the drug, the researchers reported in the journal Clinical Cancer Research.

“In the future, such tests may be used to guide the treatment of patients with the SOD2 variation, ensuring that they receive a therapy that is more effective than cyclophosphamide-based therapies,” Dr. Stefan Ambs of the National Cancer Institute, who worked on the study, said in a statement.

The researchers studied 588 breast cancer patients in the United States and Norway. Some got chemotherapy, and some did not.

Of the patients given chemotherapy, those who had variations of SOD2 fell into two groups. Women with one form of SOD2 had a higher risk of dying than others. And women with a second variation of SOD2 had the highest risk of dying in the study.

Then the researchers broke down the groups according to the specific chemotherapy drugs - doxorubicin, 5-fluorouracil, or cyclophosphamide.

Doxorubicin and cyclophosphamide kill cells by generating charged particles called reactive oxygen species.

The researchers found the SOD2 mutations best showed who would do better specifically on cyclophosphamide. Women with a distinct variant form of SOD2 who received cyclophosphamide as part of their chemotherapy regimen were the most likely to die.

The SOD2 gene produces a protein that protects cells from damage caused by reactive oxygen species.

The study adds to a growing body of research that shows ways to test cancer patients to see which drugs will work best against their particular tumors.

WASHINGTON (Reuters)