Whether a cancer treatment involves surgery, chemotherapy, radiation therapy or hormonal therapy, here’s a look at how it might affect learning and memory.
The tumor’s location affects the care team’s decisions about brain surgery. Potential cognitive effects will depend on the area of the brain affected by the procedure. Also, if an infection develops as a result of surgery in the brain, cognition can be seriously affected.
For years, oncologists believed chemotherapy could not affect cognitive functioning. Chemotherapy molecules were thought to be too large to cross the ‘blood-brain barrier’ that protects the brain. However, patients were reporting deficits in cognition during and after treatment.
A landmark study changed how clinical practice was guided in this area. The first prospective, randomized, longitudinal study providing solid evidence of chemotherapy-related cognitive dysfunction was performed at the University of Texas MD Anderson Cancer Center in Houston. Through baseline and one-year post-therapy assessments, 61 percent of participants — women with non-metastatic breast cancer — were found to have an association between cognitive dysfunction and chemotherapy. Of this subset, 45 percent remained impaired after one year in the areas of attention, processing speed, learning and memory. Also of note, a third of patients showed cognitive dysfunction prior to treatment, indicating that the disease itself contributes to brain dysfunction.
‘Chemobrain’ is real
There now have been many studies providing a great deal of additional information. What was formerly called “chemobrain” has a new name: cancer-related cognitive impairment (CRCI). Mild impairment include:
- Fine motor function
- Information-processing speed
- Learning and memory retrieval
- Organization and multi-tasking
Today, approximately 40 percent of cancer patients have CRCI before treatment. Up to 75 percent may have cognitive decline during treatment and up to 60 percent exhibit deterioration in cognition after completion of treatment. CRCI affects the occupational and social aspects of patients’ lives, usually revealing itself following the initiation of chemotherapy and up to a year after treatment is completed. Some patients experience persistent impairment.
Radiation therapy uses high-energy radiation to kill cancer cells by damaging their DNA. Treatment must be planned carefully to minimize side effects because normal cells can be damaged along with the cancer cells. Through intensity-modulated radiation therapy (IMRT), a radiation oncologist chooses the radiation doses for areas of the tumor and surrounding tissue. A high-powered computer program then calculates the number of beams required, as well as the angles of the radiation treatment.
MD Anderson Cancer Center in Houston has pioneered proton beam treatment. Proton beams differ from photon beams mainly in the way they deposit energy in living tissue. Photons deposit energy in small packets, all along their path in the tissue. Protons, however, deposit much of their energy at the end of their path, depositing less energy along the way.
Stereotactic radiosurgery, or gamma knife, delivers a large, precise dose of radiation to the tumor area in a single session via radiosurgery, or in multiple sessions via radiotherapy, a treatment without actual surgery. It may be used for some tumors in parts of the brain or spinal cord that cannot be treated with surgery or when a patient is not healthy enough for surgery.
Stages of complications
Complications of radiation therapy occur in stages:
- Acute encephalopathy may develop within two weeks. It is characterized by headaches, drowsiness and worsening of pre-existing neurologic deficits.
- Early effects may develop one to six months after radiotherapy treatment. They are associated with reversible damage to the protective covering surrounding the brain’s nerve fibers, related to disruption of the blood-brain barrier. Return to baseline is typically seen in one year.
- Late effects may develop more than a year after radiotherapy treatment and are usually not reversible. These effects consist of local necrosis of brain tissue, and are associated with mild to severe cognitive deficits.
- Whole brain irradiation often associated with metastatic disease generally results in more severe cognitive dysfunction.
Because radiation therapy can impair the growth of normal tissue and subsequent brain development, it is generally avoided in children under the age of 3.
Hormone therapies slow or stop the growth of hormone receptor-positive tumors by preventing cancer cells from getting the hormones they need to grow. The therapy is widely prescribed for patients with hormone-sensitive breast cancer, contributing to improved survival rates in a number of ways. Hormone therapies such as the drug tamoxifen attach to the receptor in the cancer cell, blocking estrogen from attaching to the receptor. Hormone therapies like aromatase inhibitors lower the level of estrogen in the body, starving cancer cells of the estrogen they need to grow. Both of these examples of hormone therapies lower the risk of breast cancer recurrence and breast cancer development in the opposite breast, as well as death from breast cancer.
A comparison study of hormonal treatments contrasted the effects of tamoxifen and the aromatase inhibitor exemestane on the cognitive functioning of post-menopausal patients with breast cancer. After a year, the study found tamoxifen was associated with lower functioning in verbal memory and executive function whereas exemestane was not.
In other studies, tamoxifen has been associated with significantly reduced performances on measures of memory, verbal fluency, visuospatial functioning and processing speed.
Assessment and treatment
Patients usually worry about work or school, as well as their ability to care for family members. The mild cognitive impairments associated with chemotherapy usually subside within a year after treatment. An assessment of cognitive functioning can help patients decide when to return to daily routines.
A neuropsychologist can assess the cognitive function of a patient. Neuropsychologists also assess a patient’s ability to return to normal daily functioning and identify other issues that can affect cognition, such as fatigue, sleep problems, and depression and anxiety.
Elements of a neuropsychological evaluation include:
- Patient history
- A battery of tests of cognitive areas often affected by cancer treatment
- Brief evaluation of psychological function and fatigue symptoms
Compensating for the deficit
To help mitigate cognitive issues, patients can adopt a number of compensatory strategies, including:
- Using a planner or calendar for appointments, events, tasks, etc.
- Making a list before going to the store
- Using cell phone alarms as reminders
- Staying organized and putting things away
- Performing tasks in a serial fashion
- Allowing extra time to complete tasks
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