Cancer survivors are significantly more likely to develop perception, thought and memory problems than those who have never been treated for cancer, say researchers.

Writing in the Journal of the National Cancer Institute, Dr Lara Heflin, from the University of Southern California in Los Angeles , USA , and colleagues explain that previous research has indicated that cancer survivors may have an increased risk of suffering from cognition problems following treatment for the disease.

To investigate further, the researchers studied 702 cancer survivors and their cancer-free twins in order to discount any genetic or early childhood influences on the risk of developing cognition problems in later life.

All the participants underwent a variety of mental health tests and interviews designed to assess their cognitive function. On a scale of one to three, anyone with a score of three, defined as having verbal, orientation or memory problems that interfered with daily life, was considered to have cognitive dysfunction.

The team found that the cancer survivors were significantly more likely to have cognitive dysfunction than their twins. Furthermore, cancer survivors were twice as likely to be diagnosed with dementia as their twins, however, this finding was not "statistically significant", say the researchers.

Although further studies are needed to confirm their findings, the researchers suggest that chemotherapy or other cancer treatments may cause long-term damage to a cancer survivor's mental capability.

Researcher Dr Beth Meyerowitz, also from the University of Southern California, said: "If, 5, 8, 10 years down the line, having had that treatment is going to increase a person's risk of dementia, that's something that should be considered by the physician and the patient."

She added: "Maybe a lower dose might be useful for the cancer but would reduce risk of cognitive dysfunction."