Some women report feelings of forgetfulness or fuzzy thinking during breast cancer treatment … problems that have collectively become known as “chemo-brain.”

But research from the University of Michigan Comprehensive Cancer Center points to the possibility that breast-cancer patients in the throes of the chemotherapy experience may be hazy because of stress, fatigue and worry, not just the therapy.

Researchers studied 56 women in line for chemotherapy or radiation treatments, in addition to 32 healthy volunteers. The women in the chemotherapy group did not perform as well on cognitive tests before or after treatment.

Brain imaging showed patients due to receive either chemo or radiation had more difficulty recruiting key brain regions needed for clear thinking.

It could be the cognitive fog of chemo-brain is related as much to fatigue and worry as the actual cancer treatments, researchers say.

The study … funded by the National Institute of Nursing Research … showed that over time, higher levels of fatigue correlated with poorer test performance and more cognitive problems.

The National Cancer Institute estimates there will be about 234,000 new cases of breast cancer in the United States this year. About twenty-five hundred of these new patients will be men.

The knowledge that chemotherapy may not always be the cause of fuzzy thinking during chemotherapy could be a relief to women worried that breast cancer treatment will cause them to lose mental sharpness.

Meanwhile, researchers think that efforts to combat stress and fatigue after a cancer diagnosis could go miles toward helping preserve strong brain function during the course of treatment.

Much more research is needed to understand the complex dynamics of chemo-brain. But slowly the fog is lifting.