Women who had chemotherapy for breast cancer showed temporary shrinking in the regions of the brain responsible for memory and concentration, Japanese researchers say.

For years, cancer patients going through treatment have complained about short-term memory and concentration problems, such as forgetting where they put keys or the names of people they know well.

Although previous research suggested the treatments may leave patients with mild cognitive impairment, some doctors thought it might be caused by hormonal changes or the anxiety of having cancer.

In the latest study, published in Monday's issue of the journal Cancer, Dr. Masatoshi Inagaki at the National Cancer Centre Hospital East in Chiba and his colleagues used MRIs to compare brain structures in 51 cancer survivors who received chemotherapy to 54 who did not.

Yoga instructor Judy Mirus noticed she was clumsy during chemotherapy.
(CBC)

The experiment was repeated for 132 cancer survivors who had cancer surgery less than a year earlier. Of this group, 73 received chemo and the rest did not.

Within a year of surgery, sections of the brain involved in cognition — such as concentration, multitasking and memory — were smaller in the women who received chemotherapy than in those who didn't, the researchers said.

The good news is, the differences reversed themselves three years after surgery, the researchers found. The finding shows the brain is resilient and that the fog of chemotherapy eventually lifts.

There were no significant differences in brain structure between cancer survivors and healthy subjects, which suggests the disease itself does not affect brain structure.

Researchers don't know the mechanism behind chemobrain, said Dr. Jeanette Vardy, an oncologist at Toronto's Princess Margaret Hospital. The brain scans Vardy studies also show changes after chemotherapy, but the side-effect is mild, compared with the risk of not getting the treatment.

It's hoped that newer chemotherapy drugs will have less of an effect on the brain, says Dr. Jeanette Vardy.
(CBC)

Doctors are starting to use different chemotherapy drugs that they hope will have less of an effect on the brain, Vardy said.

It's been three years since Judy Mirus, a yoga instructor in Edmonton, finished chemotherapy for her breast cancer. Mirus still has problems with spelling and remembering appointments, but said a little mental fog is not much of a price to pay for being alive.

"People set up their own ways of retraining themselves, and I think I've done that," Mirus said.