Breast cancer patients receiving zaps of "prophylactic" radiation therapy to prevent brain metastases while on a drug regimen were no more likely to have cognitive dysfunction than women opting for the drugs alone, according to a new study.

The small clinical trial found cognitive performance scores between the 13 women randomly assigned to receive radiation therapy and the 17 women who chose just to take trastuzumab (Herceptin) were nearly the same, MedPage Today reports.

No survival differences between the two groups emerged during the two-year-long, prospective, randomized study, presented at the San Antonio Breast Cancer Symposium on December 10, the paper said.

However, fewer women receiving the radiation went on to get brain metastases: three women receiving cranial radiation eventually developed metastases, versus seven in the no-radiation group. But because of the small size of the study, the difference was not statistically significant, according to the researchers, led by Dr. Peter Canney, an oncologist with Beatson West of Scotland Cancer Centre in Glasgow.

Canney said nearly a third of women diagnosed with HER2-positive metastatic breast cancer will go on to have brain metastases. But he said doctors are often reluctant to prescribe preventative radiation therapy out of concerns it would produce cognitive deficits, and he therefore had trouble recruiting patients for the study.

In the study, the patients randomly assigned to the radiation group got 30 Gy in 10 fractions, and were followed up every three months for nine months. None of the women had statistically significant scores on tests for depression, anxiety or quality of life, MedPage said.