MONDAY, Feb. 27 (HealthDay News) -- "Chemo brain," the name given to the mental fog and related memory problems that can occur during and after chemotherapy, may last for two decades after breast cancer treatment, new research suggests.

In the new study, 196 women with breast cancer who were treated with chemotherapy roughly 21 years earlier performed worse on tests of their memory, processing speed and other thinking ("cognitive") skills when compared to their counterparts who had never been diagnosed with cancer.

Participants had all been treated for breast cancer with a chemotherapy combination that included the drugs cyclophosphamide, methotrexate and 5-fluorouracil between 1976 and 1995. This regimen was considered the standard of care for breast cancer worldwide from the 1970s to the 1990s and was received by thousands of women during this time. Women in the study were aged 50 to 80.

"To our knowledge, this is the first study to suggest that subtle cognitive deficits may be among the long-term effects of chemotherapy, especially of the earlier regimens," study author Sanne Schagen, a group leader at the department of psychosocial research and epidemiology at the Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital in Amsterdam, said in a news release from the American Society of Clinical Oncology.

She added that while the results don't suggest that breast cancer survivors need to be watched more closely for memory and thinking problems, they could guide referrals to support services as needed.

In general, women who received this chemotherapy regimen had lower scores on tests of their ability to recall words, information-processing speed, and coordination of thinking and hand movement, such as putting pegs in a board, than women who did not. The results on these tests were similar to those seen among people who had just completed chemotherapy, and their magnitude was comparable to roughly six years of age-related decline in mental function, the study authors noted.

The researchers also assessed the women for depression and self-reported memory problems as part of the study. The women who had received chemotherapy also had more memory complaints than their peers who did not have chemo, but these complaints were not related to how they performed on memory tests.

The study findings were published online Feb. 27 in the Journal of Clinical Oncology.

Dr. Tim Ahles, the director of the Neurocognitive Research Laboratory at Memorial Sloan-Kettering Cancer Center in New York City, said this new study is the first to illustrate that long-term breast cancer survivors are still experiencing difficulty with their thought processes. "It adds to the notion that these effects may be long term and permanent," he said.

The effects of so-called chemo brain vary from person to person, and not all people who receive chemotherapy will develop or be affected by these issues.

"If someone is a professional who has an extremely demanding job, even a small change may be problematic, whereas for someone who is retired and has a more relaxed lifestyle, it may be less of a problem," Ahles said. "For women who are newly diagnosed and looking at treatments, it is still important to know that not everyone experiences these deficits."

In terms of prevention and treatment, there are more questions than answers right now. "This is an active area of research, and now that we have identified this is a real problem, people are turning their attention to what we can do to help treat and reduce some of the negative impact," Ahles noted.

Dr. Marisa Weiss, president and founder of Breastcancer.org and director of breast radiation oncology and breast health outreach at Lankenau Medical Center in Wynnewood, Pa., said the new study "shows only a few pieces of this complex puzzle."

She said it wasn't clear whether subtle losses in mental function were due to cancer alone, the effects of other therapies such as anti-estrogen treatments, or other factors.

Although the study uncovered an association between the cancer treatment and memory problems in the study patients, it did not prove a cause-and-effect relationship.

"There were many differences between these two groups," Weiss said, including whether or not they underwent the specific chemotherapy regimen. "We still need to fill in the other puzzle pieces before we can see what the picture is going to look like."

Dr. Stefan Gluck, a professor in the department of medicine and assistant director of the University of Miami/Sylvester Comprehensive Cancer Center, said that the new findings confirm this is not a temporary problem. "It may be the combination of drugs used 20 years ago were more likely to cause these issues," he said. "Today's drugs may be less likely to cause long-term cognitive effects."

He also added that drugs taken by many breast cancer survivors to stave off a breast cancer recurrence after treatment may also contribute to chemo brain.

More information

Learn more about coping with chemotherapy side effects from the U.S. National Cancer Institute.