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Chemo Brain Could Be Hormonal Therapy Brain

A small study suggests that hormonal therapy medicines may contribute to chemo brain more than chemotherapy does.
Oct 14, 2013.This article is archived
We archive older articles so you can still read about past studies that led to today's standard of care.
Many women who get chemotherapy to treat breast cancer say they have problems remembering, thinking, and concentrating during and after treatment. These problems are commonly called “chemo brain” or “chemo fog” -- doctors call these issues “cognitive impairment” or “cognitive problems.”
Some women may have trouble with:
  • learning new tasks
  • remembering names
  • paying attention and concentrating
  • finding the right words
  • multitasking
  • organizing thoughts
  • making decisions
  • remembering where things are (keys, glasses, etc.)
A small study suggests that hormonal therapy medicines may contribute to chemo brain more than chemotherapy does. Professional Advisory Board member Hope Rugo, M.D., clinical professor of medicine at the University of California-San Francisco Helen Diller Family Comprehensive Cancer Center, led the study.
The study was presented at the 2013 Breast Cancer Symposium on Sept. 10, 2013. Read the abstract of “Prospective study of cognitive function (cog fcn) in women with early-stage breast cancer (ESBC): predictors of cognitive decline.”
After surgery and other treatments, women diagnosed with early-stage, hormone-receptor-positive breast cancer usually take some type of hormonal therapy medicine to lower the risk of recurrence (the cancer coming back). Tamoxifen is the hormonal therapy medicine that has been approved the longest and is approved to treat both premenopausal and postmenopausal women. Research has shown that taking tamoxifen for 10 years instead of 5 offers more benefits, so many women are now taking tamoxifen for 10 years. The other main type of hormonal therapy medicines are aromatase inhibitors, which are approved to treat only postmenopausal women. Most women take an aromatase inhibitor for 5 years.
Women who’ve received chemotherapy to treat breast cancer have long complained about chemo brain. Still, doctors haven’t been able to find physical evidence that allowed them to diagnose the condition. Others wondered if chemo brain really exists. Some doctors think the condition is related to depression and anxiety instead of chemotherapy.
This study was a prospective study, which is the strongest type of study. A prospective study means the researchers followed a group of similar people over time to see if specific treatments predicted who would have cognitive problems.
There were 69 women in the study who were classified according to the type of treatment they received after surgery to remove early-stage breast cancer:
  • chemotherapy and 5 years of an aromatase inhibitor (33 women)
  • 5 years of an aromatase inhibitor only (22 women)
  • chemotherapy only (14 women)
Women who had received chemotherapy or radiation to the central nervous system in the past, or women who had a history of psychiatric illness, serious head injury, brain/nervous system disease, or substance abuse were excluded from the study.
The researchers tested the women’s cognitive functions, as well as their mood and fatigue, at the beginning of the study and then again 1 month, 9 months, and 18 months after the study started.
One month after the study started, about 25% of the women had lower test scores than they did when the study started. After 9 months, 35% of the women had lower scores, and after 18 months, 30% of the women had lower scores. The scores for decision-making and language function were affected the most.
Using a math formula, the researchers determined that hormonal therapy seemed to be the only factor linked to cognitive problems. Chemotherapy, fatigue, and depression weren’t linked to cognitive problems. The researchers concluded that hormonal therapy seems to be a risk factor for memory and thinking problems.
The good news is that most women who have memory and thinking problems during breast cancer treatment recover and are able to remember and think clearly after treatment is done. Still, a small number of women continue to have problems for a year or more after treatment ends.
If you’ve been diagnosed with breast cancer and are having thinking and memory problems, there are things you can do to help yourself. You might want to check out the transcript of’s Ask-the-Expert Online Conference on Managing Chemo Brain to read about other women’s experiences and questions, as well as the answers from medical experts. You’ll find tips on:
  • managing memory challenges
  • keeping your mind alert
  • getting more and better quality sleep
  • staying safe when you’re not so alert
Stay tuned to Research News for the latest information on chemo brain and its causes.

— Last updated on February 22, 2022, 9:53 PM

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