Previous research has raised concerns about a possible link among cancer, cancer therapies and cognitive dysfunction. This study found that long-term cancer survivors were at increased risk of cognitive impairment.
An accompanying editorial urged a cautious interpretation of the results pending further research.
In the study, USC psychologists studied 702 cancer survivors and their cancer-free twins in the Swedish Twin Registry.
Studying twins removes statistical influences from genetic or early childhood causes of both cancer and cognitive deficits.
Working with colleagues at the Karolinska Institute and Gothenberg University in Sweden, the researchers evaluated the survivors through a standardized mental status interview.
Participants were scored on a scale from zero to three. Anyone who scored a three, defined as having verbal, orientation or recall problems that interfere with daily life, was considered to have cognitive dysfunction.
"The twin who had cancer was more likely to have some sort of cognitive dysfunction," said Beth Meyerowitz, professor of psychology in the USC College of Letters, Arts and Sciences. About 15 percent of the cancer survivors in the study showed cognitive dysfunction.
Previous studies have found cognitive problems in short-term cancer survivors, said coauthor Lara Heflin, a doctoral student in psychology at USC. This study is the first to find significant cognitive differences between long-term survivors and cancer-free individuals, she said, and to focus on older adult survivors.
"This suggests that possibly the cognitive dysfunction gets worse over time with increased survival duration," Heflin said.